MCAT Biology Flashcards
If a viral antigen were to bind to the receptors on the surface of a B lymphocyte, which of the following immune responses would NOT occur?
Secretion of toxins by the B lymphocyte that destroy nearby virus-infected cells (NATURAL KILLER / CYTOTOXIC T CELLS NOT B LYMPH)
Which of the following gel electrophoresis diagrams obtained from DNA sequencing analysis represents this sequence?
Look for 5’ end on diagram and look for the same sequence from 5’ end to 3’ end (ALL DIAGRAMS)
A scientist sequences the genomes of several species and analyzes their evolutionary relationships to a single common ancestor. The percentage of similarity between the genome of each species to the genome of this ancestor is calculated and shown in the table below. Which species diverged from the common ancestor first? Species A = 95% Species B = 88% Species C = 35% Species D = 22%
Species D as it has the least similarity to the common ancestor, which means that this species had more time to undergo genetic mutations as well as genetic drift. These two phenomena result in a differing genome as time progresses.
Camels inhabit water-deficient environments and exhibit an evolutionary adaptation that allows them to absorb more water than their ancestors that dwelled in water-rich environments. The diagram below shows the structure of two nephron types present in the kidneys of camels and other mammals. How would the number of cortical nephrons differ from the number of juxtamedullary nephrons in camels and their ancestors?
Higher number of juxtamedullary and lower number of cortical nephrons. The deep loops in juxtamedullary allow for increased water absorption, which camels need when water is scarce.
Which of the following diagrams shows the structure of the cloned (cldnk) gene after digestion with (EcoRI) and (Xhol)?
Check to see which the restriction enzymes are cutting. Look for palindromes and overhands (sticky ends). Check the DNA sequence of each gene and figure out what the final product should look like.
What is the size of the pSKII plasmid after it is digested by EcoRI and Xhol and the cldnk gene is inserted?
Look for overall base pairs for plasmid, how many between each gene being inserted and how many for cldnk. In this instance plasmid equals 2958 plus 915 for cldnk and MINUS the removed genes, at 32 base pairs (EcoRI and Xhol). This equals 3841 bp.
What observation could have led researchers to conclude that cldnk is expressed in oligodendrocytes?
An RNA probe that was complimentary to cldnk mRNA hybridized in cells that express plp1a. (TO DETERMINE WHETHER A CELL EXPRESSES A SPECIFIC GENE, TISSUES MAY BE INCUBATED WITH A LABELLED RNA STRAND THAT IS COMPLIMENTARY TO THE mRNA OF INTEREST.)
Microarrays are chips that contain hundreds of microscopic wells, each of which can detect a distinct nucleic acid. Prior to exposure to cDNA, the wells if the microarray described in the passage most likely contained…?
Single-stranded DNA corresponding to the sense strand of zebrafish genes. (BECAUSE mRNA HAS THE SAME SEQUENCE AS THE SENSE STRAND OF GENOMIC DNA, cDNA WILL HAVE THE SAME SEQUENCE AS THE ANTISENSE STRAND. ACCORDINGLY, cDNA HYBRIDIZES WITH SINGLE-STRANDED DNA THAT CORRESPONDS TO THE SENSE STRAND OF GENOMIC DNA
Which experiment could confirm that the cldnk gene product is required for myelination?
Compare myelin formation in wild-type zebrafish to that in zebrafish with cldnk knocked out. (A GENE’S BIOLOGICAL FUNCTION CAN BE INFERRED BY COMPARING THE DIFFERENCES IN ORGANISMS WITH THE GENE KNOCKED OUT TO WILD-TYPE ORGANISMS.)
How would expression of cloned cldnk differ from expression of the endogenous gene?
Expression of the cloned gene does not involve splicing whereas expression of the endogenous gene does. (RNA POLYMERASE TRANSCRIBES BOTH EXONS AND INTRONS TO FORM PRE-mRNA. DURING RNA PROCESSING, INTRONS ARE REMOVED BY SPLICING TO YIELD MATURE mRNA. cDNA IS GENERATED FROM MATURE mRNA AND DOES NOT CONTAIN INTRONS, SO IT IS NOT SPLICED DURING EXPRESSION.)
The genetic code is said to be degenerate because there are 64 different codons, but translation produces only 20 unique amino acids. The degeneracy of the genetic code is due to which mechanism?
A) Exclusion of protein coding regions from mature mRNA
B) Errors during tRNA charging
C) Ambiguity of the tRNA for the amino acid
D) Nontraditional base pairing of anticodon with the third base of the codon
D.
The genetic code is considered “degenerate” because more than one codon can code for the same amino acid. This occurs because the third position of the mRNA codon and tRNA anticodon can undergo nontraditional base pairing, allowing a single tRNA molecule to bind to different codons.
Stenosis is the abnormal narrowing of a tubular structure in the body, such as a blood vessel. Stenosis of the afferent arterioles in the kidney would be expected to:
A) Decrease the glomerular filtration rate
B) Increase blood flow to the glomeruli
C) Decrease resistance in the afferent arterioles
D) Increase output of urine
A
The volume of fluid filtered through the kidney per unit time is known as the glomerular filtration rate (GFR), which can be modulated by controlling blood flow through the glomerulus. Higher hydrostatic (blood) pressure in the glomerulus increases GFR, and lower pressure decreases GFR.
Which of the following helps maintain the resting membrane potential of a neuron?
I. Passive transport
II. Adenosine triphosphate
III. Membrane selective permeability
A) II only
B) III only
C) I and III only
D) I, II, and III
D
The presence of protein channels in the cell membrane allows passive transport of certain ions down their electrochemical gradient. This selective membrane permeability is responsible for generating the resting membrane potential in nerve and muscle cells. Active transport pumps help maintain the concentration gradient and are critical for maintaining the resting membrane potential.
Which statement most accurately describes the role of T tubules in skeletal muscle cells?
A) T tubules bind acetylcholine at the neuromuscular junction to generate a depolarizing stimulus.
B) Depolarizing current reaches the sarcoplasmic reticulum by traveling down T tubules
C) Muscle contraction is driven by the sliding of T tubules across one another in the sarcomere.
D) T tubules sequester Ca2+ out of the cytosol to prevent prolonged muscle contraction
B
For a skeletal muscle cell to contract, Ca2+ must be released into the cytosol from the sarcoplasmic reticulum (SR). Ca2+ release is induced when a depolarizing current (action potential) runs along the sarcolemma and travels down the T tubules. This current causes the nearby SR to open its Ca2+ channels, allowing Ca2+ ions to flow into the cytosol and induce the sarcomeric actin-myosin interactions required for muscle contraction.
The relationship of delta P to cardiac output (CO) and vascular resistance (VR) is given by:
Change(P) = CO x VR
Given this, which of the following physiological changes would cause increased VR within vessels of the circulatory system? (Note: Assume all other physiological factors remain constant.)
A) Increased vasodilation of arteries
B) Heightened activity of the SA node
C) Reduced ventricular filling prior to contraction
D) Decreased arterial blood pressure
C
Rearrange to get changeP/CO = VR
Any increase in P, OR decrease in CO will ultimately INCREASE VR.
The attending physician orders an electrocardiogram (ECG) to measure the electrical activity of the patient’s heart. The results of the ECG of a healthy individual at rest (A) and the ECG of the patient at rest (B) are shown below. THERE ARE 2 BEATS ON DIAGRAM (A) AND 4 BEATS ON DIAGRAM (B)
Which of the following conclusions regarding the patient’s cardiac function is best supported by these results?
A) Atrial contraction occurs less frequently than in the healthy individual
B) APs are fired less frequently from AV nodal cells in the patient than in the healthy individual
C) Ventricular depolarization occurs for a longer time period in the patient than in the healthy individual
D) Influx of positive ions into SA nodal cells occurs more rapidly in the patient than in the healthy individual
D
Heart rate is regulated by the activity of specialized clusters of self-depolarizing cells known as SA and AV nodes. APs are initiated in the SA node and travel through the atria, stimulating atrial contraction. These APs then reach the AV node and, after a brief delay, are relayed to ventricular cells, stimulating ventricular contraction.
As shown below, CO2 reacts with water in the blood to form H2CO3, a weak acid that can reversibly dissociate to form HCO3- and a free H+ ion.
CO2 + H2O <> H2CO3 <> HCO3- + H+
The patient is noted to have decreased pulmonary gas exchange. Given this, which of the following is most likely to occur in the patient’s blood if this condition is left untreated?
A) More H2CO3 will be produced and blood pH will decrease
B) Less H2CO3 will be produced and blood pH will increase
C) More H+ ions will be present and blood pH will increase
D) Less H+ ions will be present and blood pH will decrease
A
Pulmonary gas exchange facilitates the removal of CO2 from the blood. The amount of circulating CO2 affects blood pH by shifting equilibrium of the bicarbonate buffer system. Impaired gas exchange in the lungs will decrease blood O2 levels and increase blood CO2 levels, causing respiratory acidosis as H+ concentration increases.
A 63-year-old male patient collapsed while exercising and was hospitalized. The patient presented with an elevated heart rate, low systemic blood pressure, and abnormally low blood oxygen levels. In addition, x-rays revealed excess fluid in his lungs.
Given the information in the passage, the excess fluid in the patient’s lungs is most likely caused by which of the following at the pulmonary sites of gas exchange?
A) Increased protein concentration in the blood flowing through pulmonary capillaries
B) Decreased osmotic pressure in the interstitial fluid surrounding the pulmonary capillaries
C) Increased hydrostatic pressure within pulmonary capillaries
D) Decreased volume of blood flowing through the pulmonary capillaries
C
Blood flowing through capillaries exerts hydrostatic (blood) pressure on the vessel walls that forces some fluid from the vessel into the interstitial space. If this pressure is higher than reabsorption rates from lymph and capillaries, fluid will build up.
The cell cycle of Trypanosoma brucei differs from that of higher eukaryotes. For example, the chromatin does not condense during mitosis, and the nuclear envelop remains intact. In addition, the nucleus divides before cell division, and the cell divides along the longitudinal axis.
T. brucei cells and higher eukaryotes are similar since they both undergo:
I. Interphase
II. Prophase
III. Cytokinesis
A) I only
B) I and II only
C) I and III only
D) I, II, and III
C
The cell cycle consists of interphase (G1, S, and G2) and mitotic (M) phase. In M phase, chromosomes are segregated into two nuclei. During the first phase of M phase (prophase), chromatin condenses into chromosomes and the nuclear envelop disintegrates, allowing the cell to progress into the remaining phases of M phase (meta, ana and telophase). Cytokinesis, or the division of the cell membrane, then yields two daughter cells.
A culture of T. brucei was arrested in S phase of the cell cycle by overnight incubation with the reversible inhibitor hydroxyurea. The cells were then washed, and their progression through the cell cycle was monitored by flow cytometry and microscopy.
Why were T. brucei cells incubated with hydroxyurea overnight and washed afterward?
A) To ensure that most cells were in the same phase of the cell cycle at each time point measured
B) To determine how inhibition of DNA synthesis the progression of the cell cycle
C) To limit the size of the T. brucei cells prior to their entrance into mitosis
D) To promote synthesis of the proteins needed for entry into mitosis
A
A random population of cells will likely contain some cells in each phase of the cell cycle. Study of their progress through the cell cycle requires that these cells first be brought to the same phase of the cell cycle (synchronized). These synchronized cells can then be monitored when they are released and progress through the cycle together.
A subset of the T. brucei culture was first exposed to the drug VX-680, which arrests cells upon completion of metaphase.
Based on the passage, VX-680 most likely inhibits:
A) Synthesis of transcription factors
B) Replication of the cell’s genome
C) Chromosome alignment on the metaphase plate
D) Migration of sister chromatids to opposite poles of the cell
D
Mitosis typically consists of four phases: Prophase, in which the nuclear envelope disintegrates and chromatin condenses; metaphase, in which chromosomes align on the metaphase plate; anaphase, in which sister chromatids migrate toward opposite poles of the cell; and telophase, in which nuclear envelopes reform and chromatin reverts to its uncondensed form.
Marine teleosts (bony fish) live in an aquatic environment where there is a higher external concentration of salt and a lower concentration of water relative to the internal concentrations. Owing to these conditions, salt ions tend to diffuse into the teleost through its skin, whereas water molecules within the organism osmotically traverse the opposite path.
Scientists also study freshwater teleosts, which live in an environment where there is more water and less salt outside their bodies than inside. Osmoregulation in freshwater teleosts would most likely serve to combat their natural tendency to:
A) Lose water and salt
B) Absorb water and salt
C) Absorb salt and loss water
D) Lose salt and absorb water
D
In the absence of external energy input, molecules in solution diffuse from areas of high concentration to low concentration. Osmoregulation provides the energy needed to reverse this process and maintain constant salt and water concentrations within an organism.
An eel was transported into seawater that had been treated with the volume marker phenol red. After 20 hours, the eel’s gut contained 2.3mL of fluid but showed a phenol red concentration equivalent to 12.3mL of ingested seawater. Researchers found that the eel lost 2.3g of weight due to urine output.
Which of the following conclusions about the eel can be made based on the experiment in the passage? (Note: Water density is 1g/mL.)
A) The eel absorbed 12.3mL of water through the gut
B) The eel drank 10mL of water
C) The eel lost 7.7mL of water
D) The eel excreted 4.6mL of water renally
C
Intestinal fluid ingestion, weight loss as water, and renal and extrarenal mechanisms of fluid excretion must be taken into account when calculating an organism’s fluid volume.
Teleosts with either glomerular kidneys or aglomerular kidneys that are purely tubular have served as experimental subjects for the study of marine teleost osmoregulation. Analyzing the ionic [Na+, Cl-, Mg2+, SO4(-2)] concentration of intestinal fluids, urine, and plasma in each species led to the discovery that the renal tubule of the goosefish has both excretory and reabsorptive functions.
Based on the passage, to confirm that the inorganic composition of marine teleost urine is independent of glomerular function, researchers would most likely have to discover:
A) Higher urinary concentrations of Mg2+ and SO4(-2) in the eel than in the goosefish
B) Higher urinary concentration of Cl- and Na+ in the eel than in the goosefish
C) Equally high urinary concentrations of Mg2+ and SO4(-2) in the eel and the goosefish
D) Equally high urinary concentrations of Cl- and Na+ in the eel and the goosefish
C
To claim that a particular function is independent of an anatomical structure, researchers must show similar function-related findings in organisms with and without the anatomical structure of interest.
Norepinephrine and epinephrine are water-soluble compounds, and their actual secretion into the bloodstream is stimulated by acetylcholine (ACh)-mediated signaling in the sympathetic component of the autonomic nervous system.
Administration of a drug caused increased secretion of norepinephrine and epinephrine by the adrenal medulla. This most probably occurs because the drug:
A) Increases secretion of ACTH
B) Inhibits production of TH and AADC
C) Mimics the activity of sympathetic neurons
D) Activates enzymes that mediate the breakdown of tyrosine derivatives
C
The autonomic nervous system is divided into the parasympathetic and sympathetic divisions, which are generally antagonistic in function. Although most tissues are innervated by both sympathetic and parasympathetic motor fibers, the adrenal medulla is unique in that it is only innervated by the sympathetic nervous system and thus the drug must mimic the activity.
The adrenal medulla is a collection of irregularly shaped cells located in the interior portion of each adrenal gland. In response to changing serum levels of corticosteroid hormones, medullary cells synthesize and secrete the catecholamines norepinephrine and epinephrine.
Hormones secreted by the adrenal medulla most likely influence energy metabolism by:
A) Inhibiting proteins that mediate glycogen synthesis
B) Activating their cytosolic receptors in target cells
C) Reducing the activity of enzymes that catalyze fat hydrolysis
D) Increasing the activity of proteins that inhibit gluconeogenesis
A
Energy metabolism refers to the processes by which the body manages cellular energy stores. The adrenal gland increases the body-wide level of free cellular energy sources by releasing glucocorticoids, norepinephrine, and epinephrine. Short term response, that needs glucose / energy.
For individuals who exhibit insufficient hormone production by the adrenal cortex, ACTH is sometimes administered as a treatment option. Clinicians have reported that most patients fail to respond to this treatment with ACTH. The most likely reason for this outcome is that non-responsive patients:
A) Release insufficient amounts of ACTH from the pituitary gland
B) Continuously overexpress the genes for DBH and PNMT
C) Exhibit impaired cholesterol synthesis in the smooth endoplasmic reticulum of adrenocortical cells
D) Express an overactive ACTH receptor on cells responsive to cortisol
C
ACTH is released by the anterior pituitary and acts on the adrenal cortex to promote the synthesis and secretion of cortisol, a steroid hormone produced from cholesterol. However, the actual synthesis of this steroid hormone depends on the production of cholesterol by smooth E. reticulum proteins, not ACTH. Consequently, defective SER proteins may compromise cortisol synthesis within the adrenal cortex regardless of ACTH stimulation.
A woman with low serum cortisol due to partial adrenal dysfunction is treated with high doses of a synthetic cortisol analogue. According to the negative feedback loop that synthesizes and inhibits cortisol production, treatment with a cortisol analogue will likely cause this patient’s serum level of endogenous cortisol to:
A) Increase only
B) Decrease only
C) Remain the same
D) Increase at first, but then decrease over time
B
The analogue will be able to mimic the effect of cortisol by binding hypothalamic and pituitary cortisol receptors. This interaction will increase negative feedback and reduce the synthesis and secretion of natural cortisol by the adrenal glands.
Skeletal muscle samples of adult mice were surgically harvested, washed, and stripped of connective tissues. Next, the isolated muscle samples were placed in a 150-mL oxygen-infused, electrolyte-rich bath containing glucose and Ca2+ ions that were able to enter the muscle fibers and enable maximal contractile force.
Why was Ca2+ added to the oxygen-infused, electrolyte-rich bath? To allow Ca2+ to:
A) Be sequestered inside the sarcoplasmic reticulum of the muscle fibers
B) Enter the mitochondria to promote sufficient ATP production by muscle fibers
C) Increase the affinity of muscle fiber myoglobin for oxygen
D) Facilitate the binding of ACh to its receptor on the muscle fiber
A
The sarcoplasmic reticulum (SR) is a muscle fiber organelle that tightly regulates intracellular calcium (Ca2+) concentration. The release of calcium from the SR promotes muscle fiber contraction whereas the transport of calcium into the SR promotes and maintains muscle relaxation. Since the muscle was isolated, not pre synaptic junction is available for Ca2+ ions, thus collects in SR.
In humans, skeletal muscles are innervated by the somatic nervous system and function to mediate:
A) Blood pressure regulation
B) Heart contraction
C) Propulsion of food contents along the digestive tract
D) Movement of the jaw during chewing
D
The somatic and autonomic nervous systems are the two branches of the peripheral nervous system. Voluntary activities occur through the contraction of skeletal muscle, which is mediated by the somatic nervous system. Autonomic activities are mediated by subconscious and not under voluntary control.
A mutant muscle is found to exhibit normal musculoskeletal function following the administration of anti-nAChR (anti acetylcholine receptor protein) antibodies. Compared to a wild-type mouse, this mutant mouse is most likely to show which of the following changes at the neuromuscular junction?
A) Decreased ACh degradation within the synapse
B) Reduced expression of nAChR by skeletal muscle fibers
C) Decreased reuptake of ACh degradation byproducts into the presynaptic neuron
D) Reduced release of ACh from the presynaptic vesicles
A
Acetylcholine (ACh) degradation within the neuromuscular junction is one process by which muscle fiber contraction is terminated. However, decreased ACh degradation would allow more ACh molecules to remain in the synapse and prolong stimulation to nAChR and subsequent muscle contraction.
In the combined population of 15 X chromosomes and 5 Y chromosomes, which of the following alleles, if any, would be most susceptible to loss due to random chance alone?
A) An allele on the Y chromosome
B) An allele on the X chromosome
C) An allele on either the X or Y chromosome
D) Allele loss due to random chance alone would only occur in non-sex chromosome
A
Genetic drift refers to random genetic changes in allele frequency that are due to chance events (not natural selection). Low-frequency alleles have an increased probability of being lost by genetic drift compared to those present at higher frequencies.
If researchers were to artificially express the SRY gene in WT,XX female rabbit embryos, then these rabbits would most likely develop:
A) Male characteristics, because Sp1 expression would increase and induce testis development
B) Male characteristics, because expression of SRY would induce testis development
C) Female characteristics, because the ratio of X and Y chromosomes dictates the sex in mammalian organisms
D) Female characteristics, because X chromosome inactivation in WT,XX females is not affected by SRY expression
B
Mammalian sex is determined by the expression of the SRY gene on the Y chromosome. In males (XY), SRY expression induces the development of male sexual characteristics. In females (XX), the lack of SRY expression leads to the development of female sexual characteristics.
A gene expression assay shows that the SRY gene is expressed in male embryos during the early stages of development. Which of the following best describes the DNA methylation pattern exhibited by the SRY gene in embryonic gonadal cells compared to embryonic cardiac cells.
A) The SRY gene will have higher levels of methylation in embryonic gonadal cells
B) The SRY gene will have lower levels of methylation in embryonic gonadal cells
C) The SRY gene will have similar levels of methylation in both cell types
D) The comparison cannot be performed as cardiac cells do not carry the SRY gene
B
The SRY gene is crucial for male sex determination, meaning it is most likely highly expressed in cells important to male sexual development (gonadal cells). The SRY gene in gonadal cells will likely exhibit higher expression than the SRY gene in cardiac cells.
Transferrin circulating in the blood consists of 679 amino acids, but it is composed of 698 amino acids when it is post-translationally extracted from liver cells, the primary site of transferrin synthesis. Given this information, researchers would most likely be able to extract and isolate the shorter transferrin peptide from:
A) Lymph
B) The liquid portion of blood
C) All cellular elements of blood
D) The nucleus of a liver cell
B
Plasma is the liquid portion of blood, and is made up of water, electrolytes, gases, hormones, nutrients, metabolic waste, and proteins. Although derived from blood, lymph is not a component of blood. Once secreted from liver cells, the shortened transferrin enters circulation and is incorporated into the plasma.
Iron-bound Tf, known as holotransferrin (holoTf), binds TfR to form a complex that is brought into the developing erythrocyte in an endosome. Iron buildup in the liver can lead to scarfing and loss of liver function. If the change in holoTf excretion rate were to cause this form of liver damage, the rate at which holoTf is filtered from the glomerular capillaries must be:
A) Decreased due to increased Na+ reabsorption in the nephron
B) Decreased due to decreased hydrostatic pressure within the glomerulus
C) Increased due to increased urinary output from the kidney
D) Increased due to increased hydrostatic pressure within the glomerulus
B
The glomerular filtration rate (GFR) is the rate at which fluid is filtered out of the glomerular capillaries (glomerulus) and into Bowman’s capsule. Decreased GFR in the kidney will lead to increased retention of iron-bound Tf (holoTf) in the blood, which may contribute to iron buildup in the liver and subsequent organ damage.
Individuals with beta-thalassemia are at risk for developing an enlarged spleen. The resulting impairment of spleen function in these individuals would NOT affect:
A) Immune responses against viral or bacterial infection
B) Regulation of blood glucose concentration
C) Removal of aged red blood cells from the circulation
D) Storage of red blood cells
B
Spleen functions:
- Filters aged/damaged RBCs
- Reservoir for blood
- Immune response (B cell activation site, housing macrophages)
Not responsible for blood glucose concentrations
ApoTf and TfR were analyzed by SDS-PAGE under nonreducing and reducing conditions. Based on the gels shown, which conclusion is LEAST likely to be true? (Gel 1 shows ApoTf at 40 kDa and TfR at 80. Gel 2 shows ApoTf at 40 and TfR at 40 with a thicker band)
A) Gel 1 represents the nonreducing SDS-PAGE gel
B) ApoTf has a smaller molecular weight than TfR
C) ApoTf and TfR were assigned a net negative charge
D) TfR is a monomeric protein lacking disulfide bridges
D
Comparing the results of reducing and nonreducing SDS-PAGE, both techniques that separate proteins based on molecular weight, can be useful in determining whether disulfide bonds contribute to the tertiary structure of a protein. Although TfR does not split into multiple bands, it does migrate to different positions within the gels depending on the experimental condition.
Human sperm and oocytes are substantially different in all of the following aspects EXCEPT:
A) Cell volume
B) Maturation stage at birth
C) The contribution of chromosomes to a zygote
D) The rate at which they are produced
C
Egg and sperm cells are haploid cells that contribute an equal number of chromosomes to a zygote during fertilization. All other choices are significantly different for both cells.
Which of the following would likely cause an embryo to implant in a location other than the uterine lining?
A) Reduced number of fallopian cilia
B) Surge in luteinizing hormone prior to ovulation
C) Incomplete gastrulation
D) Lack of follicle rupture from the ovary
A
After fertilization, fallopian cilia help propel the fertilized oocyte toward the uterus for implantation. An inadequate number of cilia in the fallopian tube can cause implantation of the fertilized egg outside the uterus. LH and follicle rupture are needed for implantation, while gastrulation is post-implantation.
A student adds 5 bacterial cells to a test tube containing fresh medium and incubates it for 3 hours at 37*C. If the bacterial population shows an initial lag phase of 20 minutes followed by a doubling time of 40 minutes, what is the approximate number of bacterial cells present at the end of the incubation period? (Note: Assume unrestricted growth during incubation.)
A) 20 cells
B) 40 cells
C) 80 cells
D) 160 cells
C
Binary fission is the process by which a unicellular organism divides into two identical daughter cells. The generation time refers to the time in which a bacterial population doubles. When a single cell divides by binary fission, the number of cells that result is calculated by multiplying the original number of bacterial cells by 2^n, where n equals the number of generations.
Assume a single celled organism was discovered in water above 100*C. On closer inspection, it is determined that this organism was previously classified under the Archaea domain. Given this information, this organism most likely has:
A) A peptidoglycan layer in its cell wall
B) A circular chromosome
C) Telomeres
D) An endoplasmic reticulum
B
Prokaryotes are unicellular organisms that can be further classified into the domains of Archaea or Bacteria. Organisms in these domains lack a nucleus and membrane-bound organelles but have circular chromosomes and are able to reproduce asexually through binary fission. However, bacteria (not Archaea) have peptidoglycan in their cell wall as a distinguishing feature.
A scientist proposed that ectopic endometrial cells contain extra copies of the VEGF gene. Given this information, which of the following techniques can be used to analyze VEGF gene count?
I. DNA sequencing
II. Northern blot
III. Southern blot
A) I only
B) II only
C) I and III only
D) II and III only
C
DNA sequencing and Southern blotting are DNA assays that may be used to assess the relative quantity of genes between tissue types. Northern blotting is an RNA assay used to assess gene expression in different tissues.
Progesterone concentration is generally lowest in the proliferation phase and highest in the secretory phase of the menstrual cycle. The investigators conclude that VEGF concentrations within peritoneal fluid may be inversely correlated with serum levels of progesterone. Does the data support this conclusion? (Figure just shows VEGF concentration pf normal and endometriosis affected women; only difference is that VEGF concentrations are significantly higher in proliferative phase of endometriosis affected women. Both secretory phases are equal is both women.)
A) No, peritoneal VEGF concentration is lowest during the secretory phase of the menstrual cycle
B) No, serum levels of progesterone are consistently elevated in women with endometriosis
C) Yes, peritoneal VEGF concentration is highest during the proliferative phase of the menstrual cycle
D) Yes, women with endometriosis have consistently elevated peritoneal VEGF concentration
C
Changes in the serum levels of estrogen and progesterone cause the physiological changes associated with the menstrual cycle, the female reproductive cycle that repeats every 24-36 days. Interpretation of the figure will show that progesterone is inversely correlated to VEGF concentrations “in general”.
Surgical removal of the ovaries is one treatment for endometriosis. Complete removal of the ovaries would most likely result in which of the following?
A) Significant increase in bone mass
B) Degeneration of breast tissue
C) Severe immune system impairment
D) Increased frequency of menstruation
B
The ovaries are female reproductive organs that contain oocytes and secrete female sex hormones (estrogen, progesterone). These hormones influence female reproductive function, and are directly responsible for the development and maintenance of female sex characteristics.
Infertility in patients with endometriosis can result from ectopic endometrial tissue deposits in all of the following structures EXCEPT:
A) The urethra
B) The vaginal canal
C) The fallopian tubes
D) The ovaries
A
The female reproductive tract consists of the ovaries, fallopian tubes, uterus, cervix and vagina. Each of these tissues performa specialized functions that enable pregnancy and delivery. The urethra is part of the urinary tract, not reproductive.
The mechanism by which endometrial tissue successfully implants outside the uterine cavity is though to be dependent on signaling molecules that promote the formation of blood vessels locally. One of these signaling molecules is vascular endothelial growth factor (VEGF), a protein that is normally synthesized and secreted by various tissues in response to reduced oxygen levels. VEGF signaling also leads to the dilation of existing blood vessels. One function pf vasodilation is to:
A) Increase body temperature in cold environments
B) Increase blood flow to the intestines following a meal
C) Decrease blood flow to the kidneys during dehydration
D) Maintain blood pressure following an episode of fluid loss
B
Vasodilation (blood vessel widening) decreases blood pressure and increases flow to the tissues supplied by that blood vessel. Vasoconstriction (blood vessel narrowing) increases blood pressure and decreases blood flow to the tissues supplied by that blood vessel.
Which step(s) of the viral life cycle would most likely occur in lytic phages?
I. Injection of viral genetic material into the bacterial host
II. Integration of viral DNA into the bacterial genome
III. Degradation of the host genome
A) I only
B) III only
C) I and II only
D) I and III only
D
Bacteriophages use the host cell’s machinery and resources to replicate their genome and synthesize viral proteins to form new virions. Phages with a lytic life cycle replicate rapidly and release progeny via lysis of the host cell. In contrast, phages with a lysogenic life cycle integrate their genome with the host genome and replicate as the cell divides.
A subset of aggressive cancers has a relatively high growth rate, leading to the formation of large tumors. An effective drug against fast-growing tumors would most likely NOT target which stage of the cell cycle?
A) Go
B) G2
C) G2 / Mitosis checkpoint
D) G1 / S-Phase checkpoint
A
Most cells in the human body are arrested in Go. However, cellular transition into G1 prepares a cell for division and DNA synthesis (S phase). In the G2 phase, DNA is checked for errors and the cell ensures that sufficient organelles and cytoplasm are available for cell division. Subsequently, the cell divides in the M phase via mitosis and cytokinesis. Compounds that inhibit cell division typically target the cell cycle in phases G1 to M.
In a neuron, mitochondrial biogenesis is believed to occur primarily in the cell body, but mitochondria are often positioned at the presynaptic terminal, a distal site with high metabolic demand. Given this information, which molecular mechanism is most likely responsible for mitochondrial transport from the cell body to the presynaptic terminal?
A) Kinesin motors transport mitochondria along microtubules
B) Kinesin motors transport mitochondria along microfilaments
C) Dynein motors transport mitochondria along microfilaments
D) Dynein motors transport mitochondria along microtubules
A
The intracellular scaffolding of a eukaryotic cell is composed of three families of protein filaments: Microfilaments, intermediate filaments, and microtubules. Intracellular transport of cargo (organelles, vesicles) is mediated primarily by two microtubular motor proteins (kinesin and dynein). Kinesin mediates anterograde transport (away from the nucleus) whereas dynein mediates retrograde transport (toward the nucleus).
Impaired release of which of the following neurotransmitters would directly result in the paralysis of skeletal muscle?
A) Norepinephrine
B) Epinephrine
C) Glutamate
D) Acetylcholine
D
At the neuromuscular junction, acetylcholine is released via exocytosis from presynaptic motor neurons. Acetylcholine binds to receptor on the motor end plate, triggering muscle contraction. Disruption of this process causes skeletal muscle paralysis.
Which of the following cellular processes would most likely lead to increased diversity in a population of organisms?
A) DNA replication during S phase of the cell cycle
B) Synapsis involving two homologous chromosomes
C) Alternative splicing of gene transcripts
D) Cell division via mitosis
B
In eukaryotes, genetic recombination via crossover events (exchange of DNA segments between homologous chromosomes). Synapsis or the joining of homologous chromosomes into tetrads occurs during prophase I of meiosis and is required for crossing over to occur. Crossovers increase genetic diversity by mixing maternal and paternal alleles into a single chromosome that is then inherited by the offspring. Alternative splicing will result is protein diversity, not genetic.
A drug that blocks the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary would most likely:
A) Decrease secretion of cortisol from the adrenal cortex
B) Decrease secretion of thyroid-stimulating hormone from the anterior pituitary
C) Increase secretion of oxytocin from the posterior pituitary
D) Increase secretion of calcitonin from the thyroid
A
Corticosteroids (glucocorticoids and mineralocorticoids) are steroid hormones released by the adrenal cortex. The release of cortisol from the adrenal cortex is mediated by the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary.
One function of endothelial cells is to:
A) Contract to increase blood pressure
B) Line the inside of the gastrointestinal tract
C) Form clots at sites of vascular damage
D) Line the inside of blood vessels
D
Endothelial cells are a specialized type of epithelial cell that line the inside of blood vessels and lymph vessels specifically. The endothelium is a single-cell layer that makes up the innermost surface of the cardiovascular system (heart and blood vessels). The endothelium promotes blood fluidity and functions as a selective barrier between the blood and surrounding tissues.
Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR). In healthy somatic cells, TERT transcription is generally downregulated by the absence of the oncogene c-Myc and the presence of the tumor suppressor protein WT1; in cancerous somatic cells, increased telomerase activity is associated with tumorigenesis (WT1 is frequently absent and c-Myc is usually increased in expression).
WT1 and c-Myc most likely alter TERT transcription levels by doing which of the following at the TERT gene promoter?
A) Inhibiting and facilitating RNA polymerase binding, respectively
B) Inhibiting and facilitating DNA polymerase binding, respectively
C) Facilitating and inhibiting RNA polymerase binding, respectively
D) Facilitating and inhibiting DNA polymerase binding, respectively
A
DNA polymerase is involved in replication, NOT transcription. Transcription factors can upregulate or downregulate transcription by influencing the ability of RNA polymerase to bind to a promoter. Transcription factors that increase transcription are called activators and facilitate RNA polymerase binding whereas those that decrease transcription are called repressors and inhibit binding.
Considering that healthy somatic cells typically transcribe the telomerase reverse transcriptase (TERT) gene only at low levels, where in the chromosome of these cells is the gene most likely found?
A) In a relatively open, uncoiled portion of the chromosome
B) In the portion of the chromosome that binds the kinetochore
C) In a portion of the chromosome that associates with ribosomes
D) In a portion of the chromosome that is tightly wound around histones
D
Chromatin can be broadly classified as heterochromatin and euchromatin. Heterochromatin consists of DNA tightly coiled around histones and is not readily transcribed by RNA polymerase. Euchromatin is more loosely associated with histones and is more easily transcribed.
Cells thats must be able to divide indefinitely (stem cells and germ cells) express an enzyme known as telomerase. Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR). Using a portion of TR as a template, telomerase extends telomeres by continuously adding the sequence 5’-TTAGGG-3’ to the ends of chromosomes.
Based on the sequence that telomerase adds to the ends of chromosomes, the template portion of TR most likely contains which of the following sequences?
A) 5’-UUAGGG-3’
B) 3’-AAUCCC-5’
C) 5’-CCCTAA-3’
D) 3’-CCCUAA-5’
B
New nucleotide strands are synthesized using complementary strands as templates, with the two strands aligned antiparallel to each other (the 5’ end of one strand aligns with the 3’ end of the other). The DNA, guanine (G) always pairs with cytosine (C), and adenosine (A) always pairs with thymine (T). In RNA, the only difference is that uracil (U) is present instead of thymine.
In humans, conditions such as hypertension, liver disease, and Alzheimer disease have been associated with the decreased telomere length and resulting senescence that occur as part of the normal aging process. The telomerase reverse transcriptase (TERT) gene consists of 16 exons and 15 introns that can be spliced into more than 20 different isoforms in humans. Only one isoform (the active isoform) is known to extend telomeres. However, the i2 isoform has been hypothesized to downregulate residual TERT activity in somatic cells.
If the role of the i2 isoform of the TERT gene proposed is correct, individuals who express the i2 isoform in somatic cells would be expected to have a decreased risk of:
A) Hypertension
B) Cancer development
C) Alzheimer disease
D) Liver disease
B
DNA is initially transcribed as precursor mRNA (pre-mRNA), consisting of introns and exons. The pre-mRNA can then be spliced into one of several possible isoforms, each containing multiple exons, and some containing portions of introns. Many inactive isoforms are believed to help regulate the activity of active isoforms. Therefore, i2-mediated downregulation of telomerase activity in somatic cells would be expected to reduce the risk of cancer development.
Some eukaryotic organisms have multiple telomerase reverse transcriptase (TERT) genes with high sequence similarity that are expressed at different times in the organism’s life cycle. These genes could have arisen by:
A) Alternate splicing
B) Conjugation
C) Gene duplication
D) Transformation
C
Genes with high sequence identity are evolutionarily related, having a common origin. They generally arise by gene duplication and, over time, may mutate and fulfill distinct roles within an organism.
During a parasitic infection, which of the following would most likely be responsible for phagocytosis of organisms and the release of histamine, respectively?
A) Basophils, macrophages
B) Natural killer cells, T-cells
C) Macrophages, basophils
D) T-cells, natural killer cells
C
Macrophages are one of the cells responsible for phagocytosis, the process of engulfing solid particles (bacteria) designated for destruction into phagocytic vesicles called phagosomes. In contrast, basophils function to release chemical mediators such as histamine that stimulate an inflammatory response.
Which of the following cell-cell junctions would help skin cells withstand mechanical stress by directly anchoring the intermediate filaments of adjacent cells?
I. Desmosomes
II. Gap junctions
III. Tight junctions
A) I only
B) II only
C) I and III only
D) II and III only
A
Desmosomes, gap junctions, and tight junctions are cell-cell junctions that provide tissue with mechanical strength, cytoplasmic continuity, and watertight seals, respectively.
Cirrhosis of the liver is characterized by hepatic cell death, tissue scarring, and altered liver functions. All of the following would be disrupted by cirrhosis of the liver EXCEPT:
A) The production of ketone bodies
B) The metabolism of most drugs
C) The oncotic pressure within capillaries
D) The secretion of digestive proteolytic enzymes.
D
Digestive proteolytic enzymes that hydrolyze polypeptides, are synthesized and secreted from the pancreas, stomach and small intestine. The liver has various functions, including storage of glycogen, regulation of blood glucose levels, detoxification of drugs, synthesis and secretion of bile, production of serum proteins (albumin, clotting factors), and synthesis of ketone bodies.
Compared with blood in the pulmonary veins, blood in the pulmonary arteries has higher concentrations of:
I. O2
II. H+
III. CO2
A) I and II only
B) I and III only
C) II and III only
D) I, II, and III
C
Within the pulmonary circuit, the pulmonary arteries carry CO2-rich, O2-poor blood from the heart to the lungs, where CO2 is exchanged for O2. The pulmonary veins then carry CO2-poor, O2-rich blood from the lungs to the heart, which then pumps the oxygenated blood to all body tissues.
AAV2 binds to transmembrane proteins on the cell surface. The cell membrane invaginates and forms a vesicle in response to AAV2 binding. The vesicle matures to an early endosome. The endosome rides along a microtubule track toward the nucleus. The endosome lumen is acidified as it matures to a late endosome. AAV2 proteins undergo a conformational change in response to the acidic environment and form pores in the endomsomal membrane, allowing AAV2 to escape. AAV2 enters the nucleus, where it uncoats and transduces the cell.
AAV2 entry into cells could best be blocked by a drug that inhibits which of the following mechanisms?
A) Fusion of viral and cell membranes upon receptor binding
B) Formation of membrane extensions that engulf external particles
C) Inward budding of the cell in response to receptor binding
D) Constitutive invagination of the cell membrane to take up extracellular liquid
C
Cells take up their surrounding environment via endocytosis, which includes mechanisms of phagocytosis, pinocytosis, and receptor-mediated endocytosis. Many viruses use receptor-mediated endocytosis to enter cells. Enveloped viruses can also enter cells by fusing their membrane with the membrane of the cell. These are encased in a capsid and it directly fused to the cell membrane and released into the cytosol.
Which of the following is true concerning the proteins to which AAV2 binds in Step 1?
(Step 1: AAV2 binds to transmembrane proteins on the cell surface.)
A) They localize primarily in low-cholesterol environments known as lipid rafts
B) They are held statically in place by cytoskeletal component
C) They are able to interact only with the phospholipids on the outer leaflet of the cell membrane
D) They can migrate laterally through the phospholipid-rich environment of the cell membrane
D
Cell membranes are composed largely of phospholipids, which act as a fluid that allows other membrane components such as transmembrane proteins, glycoproteins, cholesterol, and glycolipids to migrate through this environment laterally. Accordingly, the structure of the animal cell membrane is known as the fluid mosaic model. Transmembrane proteins span the width of the membrane and thus must be able to migrate laterally.
Prior to reaching their final destination in the plasma membrane, the AAV2-binding proteins on the cell surface passed through all of the following cellular compartment EXCEPT:
A) The endoplasmic reticulum
B) The Golgi apparatus
C) A peroxisome
D) A secretory vesicle
C
The secretory pathway involves the processing of proteins as they go through the endoplasmic reticulum and the Golgi apparatus. After processing in the Golgi, proteins destined for the cell membrane are packed into secretory vesicles, which fuse with the plasma membrane. Other organelles, such as the nucleus, mitochondria, and peroxisomes, are not involved in the secretory pathway, and most of their proteins are translated in the cytosol.
As it matures, the endosomal lumen becomes acidified relative to the cytosol. Protons from the cytosol most likely enter the endosomal lumen by which of the following processes?
A) Simple diffusion
B) Facilitated diffusion
C) Passive transport
D) Active transport
D
Molecules can cross biological membranes by active or passive transport. Active transport involves a molecule moving against its concentration gradient and requires energy input (ATP). In contrast, passive transport involves molecules diffusing down their concentration gradient and requires no external energy. Passive transport can be divided into simple diffusion, in which molecules cross membranes directly, and facilitated diffusion, in which molecules must go through protein channels.
Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as gene therapy vector. In quiescent cells, early endosomes containing AAV2 would most likely move toward:
A) Ribosomes
B) Centrioles
C) Cilia
D) Centromeres
B
The cytoskeleton consists of actin filaments (microfilaments), intermediate filaments, and microtubules. Microtubules are involved in intracellular transport. The microtubules involved in the process originate near the nucleus on organelles called centrioles and radiate out toward the plasma membrane.
What is the fate of the virus particles that fail to escape the acidified endosome in Step 6?
(Step 6: AAV2 proteins undergo a conformational change in response to the acidic environment and form pores in the endosomal membrane, allowing AAV2 to escape.)
A) Degradation in the lysosome
B) Repackaging in the Golgi followed by exocytosis
C) Reprocessing in the endoplasmic reticulum
D) Destruction by a proteasome
A
After internalization of extracellular materials into vesicles, the vesicles containing these materials become endosomes, which then mature from an early stage to a late stage, ultimately becoming lysosomes. Endocytic cargo that does not enter alternative pathways (entry into the secretory pathway) and fails to escape from endosomes will end up in the lysosome to be degraded.
In bone tissue, RANK is expressed by precursors of mature osteoclasts, also known as osteoclast progenitor cells (OPCs). RANKL is expressed by osteoblasts adjacent to OPCs, and the binding of RANKL to RANK in these neighboring cells causes downstream effects through recruitment of TRAF6, an intracellular protein.
The cells that are most important for the differentiation of OPCs are cells that promote:
A) Calcium transfer from bone tissue into the blood stream
B) Calcium transfer from the bloodstream into bone tissue
C) Acid production in bone tissue
D) Proteolytic enzyme production in bone tissue
B
Bone remodeling is a continuous process in which osteoclasts (bone-resorbing cells) break down old bone and osteoblasts (bone-depositing cells) secrete new bone matrix. This process functions to maintain the strength and integrity of bone over time. Osteoblasts promote the precipitation of calcium and phosphate from the bloodstream and their transfer and incorporation into the bone matrix. In contrast, osteoclasts secrete acids that break down the mineral components of bone, releasing calcium and phosphate into the bloodstream. Because RANKL is expressed by bone-depositing osteoblasts, osteoclasts that promote the breakdown of bone are NOT most important in promoting OPC differentiation.
A group of scientists hypothesized that elevated RANKL signaling contributes to the decrease in bone density associated with osteoporosis. To confirm their hypothesis, they collected bone tissue samples from patients with the disease and compared them to healthy controls. RANKL is expressed by osteoblasts (bone-depositing) and RANK is expressed by osteoclasts (bone-resorption). Given this information, all of the following experimental observations would support their hypothesis EXCEPT:
A) Higher c-Fos expression in patient samples than in control samples
B) More RANK/TRAF6 association in patient samples than in control samples
C) Increased RANKL/RANK binding in patient samples than in control samples
D) Higher expression of RANK in patient samples than in control samples
D
Decreased activity of osteoblasts (bone-depositing cells) or increased activity of osteoclasts (bone-resorbing cells) can lead to reduced bone mass and density.
A student isolates the cellular components of OPCs in wild-type (WT) mice and in mutant (MT) mice exhibiting a single base substitution that causes reduced osteoclastic activity. Western blot analysis is then performed to test for NF-kB and c-Fos expression in the cytoplasm and nucleus of OPCs isolated from these mice. The results of this analysis are shown below.
(Only differences are c-Fos has a smaller band in the nucleus of MT and NF-kB has no band in the nucleus of the WT)
A) MT mice have a mutation that disables the ability of NF-kB to localize to the nucleus
B) MT mice have a mutation that prevents c-Fos from interacting with NF-kB
C) MT mice have a mutation in the DNA binding region of NF-kB
D) MT mice have a mutation that prevents the transcription of c-Fos in OPCs
A
Transcription factors have nucleus localization sequences that facilitate their entry into the nucleus, where they regulate the expression of target genes. Because NF-kB requires an intact nuclear localization sequence to enter the nucleus and increase c-Fos expression, a mutation in the NF-kB nuclear localization sequence of MT mice would best explain these results.
Cathepsin K is a proteolytic enzyme secreted by osteoclasts. In a clinical trial, patients with osteoporosis due to increased RANK-RANKL signaling are divided into an untreated group (saline placebo administered) and a treated group (cathepsin K inhibitor administered). Given the information, bone density after the trial will most likely be:
A) Increased in the untreated group compared to the treated group
B) Decreased in the untreated group compared to the treated group
C) Nearly the same in both groups
D) Nearly the same in both groups initially, but then would increase in the untreated group compared to the treated group
B
During bone resorption, osteoclasts release proteolytic enzymes that break down the organic bone matrix. In osteoporosis patients, overactivity of osteoclasts and increased release of enzymes can lead to decreased bone density across time.
The information in the passage suggests that increased activity of RANK is most likely due to signaling hormones involving which of the following hormones?
A) Parathyroid hormone
B) Calcitonin
C) Growth hormone
D) Glucagon
A
To regulate calcium homeostasis, parathyroid hormone (PTH) and calcitonin act antagonistically to each other. PTH is secreted in response to low blood calcium levels and stimulates bone resorption by osteoclasts, causing an increase in blood calcium. In contrast, calcitonin is secreted in response to high blood calcium levels and decreases osteoclast activity, ultimately decreasing blood calcium.
The diagram above represents the immature gamete of a male fly that is heterozygous for Ena. If the gamete undergoes meiotic division and Ena alleles do not undergo recombination, during which phase of meiosis will the wild-type Ena alleles be pulled to opposite poles of the cell?
A) Metaphase I
B) Anaphase I
C) Metaphase II
D) Anaphase II
D
Gamete formation requires cellular division by meiosis I and meiosis II, in which homologous chromosomes and sister chromatids, respectively, are separated. In the absence if recombination, maternal and paternal alleles are separated from each other during anaphase I, and identical alleles on sister chromatids are separated from each other during anaphase II.
The genes Abl, Enabled (Ena), and receptor protein tyrosine phosphatase (PTP) are involved in axonal guidance during neuronal development and are all believed to operate in the same pathway. Of the genes tested, which are autosomal?
I. Ena
II. Abl
III. PTP
A) II only
B) I and III only
C) II and III only
D) I, II, and III
D
Genetic traits may be autosomal or sex-linked (X chromosome). Because males have only one X chromosome, sex-linked recessive traits tend to be present at greater rates in males than in females, whereas autosomal traits are present in the same proportions in both.
Which evidence from Table 1 suggests that PTP and Abl are located close together on the chromosome?
(Table 1 shows low amounts of recombinant flies in both recombinations and a large number of parental flies)
A) The two recombinant genotypes occur with similar frequencies
B) Only a small percentage of the progeny are recombinant
C) Recombination did not occur in male gametes
D) The F1 generation has a high recombination frequency
B
Homologous chromosomes can exchange genetic material by recombining. Genes that are located close together on a chromosome have a lower probability of being separated by recombination than those that are far apart. Fewer progeny from a cross will have recombinant genotypes than will have parental genotypes.
Axonal guidance is the process through which axons reach their proper targets in the brain. Researchers hypothesize that the wild-type PTP gene product mediates proper axonal guidance by inactivating the Abl gene product. Which experimental observation would best support this hypothesis?
A) Suppression of Abl increases the severity of abnormal axonal guidance in PTP mutants
B) Overexpression of Abl reduces the severity of abnormal axonal guidance in PTP mutants
C) Suppression of Abl reduces the severity of abnormal axonal guidance in PTP mutants
D) Overexpression of Abl restores normal axonal guidance in PTP mutants
C
Upstream gene products in a biological pathway act on downstream gene products. Failure of an upstream product to act can be compensated for by alterations to downstream targets that mimic the affect of the upstream product. In effect, suppression of Abl activity carries out the same function that active PTP does and therefore should lead to the same outcome.
The gustatory-salivary reflex can be modulated (dampened or enhanced) by input higher centers in the central nervous system. Ultimately, ACh released from postganglionic neurons acts on the muscarinic acetylcholine receptors on the secretory cells of the salivary gland to stimulate salivation. To modulate the salivary response, descending pathways from the brain would most likely synapse onto which part of the reflex arc?
A) The taste receptor
B) The salivary gland
C) The preganglionic neuron
D) The postganglionic neuron
C
A reflex is an involuntary response to a stimulus that does not require input from the brain. Reflexes are mediated by reflex arcs, neuronal pathways that include a sensory neuron, an efferent neuron, and possibly an interneuron. Based on the gustatory-reflex arc, the cell bodies of both the interneuron and the preganglionic neuron lie within the spine. Therefore, descending input could act on either of these two neurons to alter the gustatory-salivary reflex.
The gustatory-salivary reflex, the secretion of saliva from the salivary glands in response to gustation (taste), is primarily mediated by the parasympathetic division of the nervous system. The gustatory-salivary reflex pathway is part of which of the following branches of the nervous system?
I. Peripheral
II. Somatic
III. Autonomic
A) I and II only
B) I and III only
C) III only
D) I, II, and III
B
The nervous system can be divided into two major branches, the central and peripheral nervous systems. The peripheral nervous system can be further divided into the sensory (afferent) and motor (efferent) divisions, with the motor division being composed of the somatic and autonomic nervous systems. Furthermore, the autonomic nervous system is divided in the parasympathetic and sympathetic branches.
In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Ultimately, acetylcholine released from postganglionic neurons acts on the muscarinic acetylcholine receptors (mAChRs) on the secretory cells of the salivary gland to stimulate salivation. The drug cevimeline hydrochloride is a cholinergic agonist. Administration of cevimeline hydrochloride would be expected to cause:
A) Increased salivation due to stimulation of mAChRs
B) increased salivation due to inhibition of mAChRs
C) Decreased salivation due to stimulation of mAChRs
D) Decreased salivation due to inhibition of mAChRs
A
Agonists are ligands that activate the receptors they interact with and induce downstream effects. Mimics the effect of acetylcholine on the mAChRs. Antagonists are ligands that inhibit the receptors they interact with and block downstream effects.
During periods of stress, many individuals experience dry mouth caused by decreased salivation. Which of the following functions would also be expected to decrease during periods of stress?
A) Gluconeogensis
B) Cardiac contraction
C) Dilation of pupils
D) Digestive peristalsis
D
The parasympathetic and sympathetic divisions of the nervous system are broadly antagonistic in their effects. The parasympathetic division promotes digestion and other tasks related to an organism’s long-term needs (rest and digest). Alternatively, the sympathetic divisions enables the organism to meet more immediate needs (fight or flight).
In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Which of the following neurons correspond to the gustatory-salivary reflex’s afferent and efferent components, respectively?
A) Sensory neuron, preganglionic neuron
B) Preganglionic neuron, sensory neuron
C) Interneuron, postganglionic neuron
D) Postganglionic neuron, interneuron
A
Afferent signals approach the central nervous system. Efferent signals exit the central nervous system. The preganglionic fibers, which transmit impulses away from the spinal cord, make up the efferent component of the reflex arc.
The graph below shows the firing rate of preganglionic neurons within the rat gustatory-salivary reflex arc when the lateral hypothalamic area (LHA) is electrically stimulated at various time intervals before the tongue is stimulated. The results are compared to the preganglionic firing rate following tongue-only stimulation, which was used a baseline that represented 100% activity. (The graph simply shows a descending trend from an interval of 50 to 250 and the chart reducing from 140% to 90%, respectively.)
A) LHA signaling has no effect on the magnitude of salivation of the reflex
B) LHA signaling increases the magnitude of salivation of the reflex
C) LHA signaling decreases the magnitude of salivation of the reflex
D) There is not enough data to determine the effect of LHA signaling on the reflex
B
Input from higher areas in the central nervous system can modulate the activity of reflexes by either strengthening or weakening the magnitude of the response.
Assume L410 is an acquired mutation that occurs only in hepatocytes of adults who were exposed to a certain mutagen. A woman with the L410 mutation has a child with an unaffected man. What is the probability that this child has the L410 mutation?
A) 0.00
B) 0.25
C) 0.75
D) 1.00
A
Mutations that occur in the reproductive cells of parents are called germline mutations. These mutations can be passed on from parent to offspring, and result in the offspring carrying the mutation in all of its cells. Parental somatic mutations, which occur in non-sex cell lineages during an organisms’ lifetime, are not inherited by the offspring.
Excess post-exercise oxygen consumption is the extra amount of oxygen consumed after the completion of exercise and before respiration returns to resting levels. This extra oxygen is used to restore muscle fibers to their pre-exercise state by doing all of the following EXCEPT:
A) Replenishing the ATP stores within the muscle fiber
B) Facilitating calcium release from the sarcoplasmic reticulum in the muscle fiber
C) Restocking the myoglobin stores within the muscle fiber
D) Supplying the ATP used to replenish glycogen stores in the muscle fiber
B
Oxygen intake remains elevated after exercise due to the increased demand in muscle cells for oxygen to replenish ATP, creatine phosphate, and glycogen stores and restock myoglobin with oxygen. The amount of additional oxygen consumed is called the excess post-exercise oxygen consumption, or oxygen debt. During rest or relaxation, calcium is sequestered into, not released from, the sarcoplasmic reticulum.
Which of the following is generally true about the path of blood flow through the heart?
A) The right ventricle contracts to propel blood to all body tissues except the lungs
B) The left ventricle pumps blood into the left atrium
C) The aorta receives blood from the left ventricle
D) The right atrium receives blood from the pulmonary veins
C
The right heart receives deoxygenated blood from the body and pumps it out toward the lungs. The left heart receives oxygenated blood from the lungs and pumps it out toward the rest of the body. Atria receive blood; ventricles release blood. The first vessel to receive blood on the way out of the heart is the aorta.
A woman carries an X-linked recessive allele for a disorder characterized by muscle degeneration but does not express this condition. If she has multiple offspring with an unaffected man, how many of the woman’s children are expected to exhibit this degenerative disorder?
A) All
B) Half
C) None
D) One-quarter
D
For the cross between a female carrier of an X-linked recessive trait and an unaffected man, only male children will express the trait. The probability of a child having the trait is given by P(child inherits affected X-chromosome from mother) x P(child is male) = 0.5 x 0.5 = 0.25. Therefore, 25% of all offspring will express the trait.
Neural tube defects (NTDs) arise from abnormalities in the development of the neural tube and can range from mild to severe, depending on which portion of the tube is affected. Spina bifida, a form of NTD, is divided into three categories. The most serious sub-classification of spina bifida is myelomeningocele, which occurs when the lower spine fails to close, which leaves the spinal cord and nerve roots in the lower back damaged and exposed. Neural crest cells migrate away from the neural tube to give rise to most of the peripheral nervous system. Given this information, would neural crest cells be involved in the pathology of myelomeningocele?
A) Yes; neural crest cells secrete signals that directly inhibit neural tube closure
B) Yes; neural crest cells fail to differentiate into the posterior spinal cord
C) No; neural crest cells continue to differentiate into glial cells of the brain
D) No; neural crest cells continue to act normally as temporary migratory cells that give rise to other cell types
D
Cell migration in embryogenesis is the movement of cells into their final positions within the embryo. The migratory action of neural crest cells during neurulation (the formation of the nervous system) gives rise to many peripheral nervous system structures. In contrast, the central nervous system is derived from the neural tube. Myelomeningocele is an issue of the spinal cord (neural tube) and not peripheral nerves (neural crest cells).
The germ layer that gives rise to the notochord also gives rise to which of the following cell types?
A) Alveolar cells
B) Osteocytes
C) Melanocytes
D) Islet beta cells
B
The three primary germ layers (endoderm, mesoderm, ectoderm) form during gastrulation. Each gives rise to particular cell types in specific organ systems. Alveolar and islet beta cells are derived from the endoderm, while melanocytes are from the ectoderm. Osteocytes are mesoderm.
Assume that neural stem cells are considered to be multipotent. Which of the following best describes the classification of stem cells?
A) They are able to differentiate into all fetal structures but not placental structures
B) They are able to differentiate into both placental and fetal structures
C) They are able to differentiate into specialized cell types of a particular tissue
D) They are able to differentiate in the zygote but not in the adult organism
C
Totipotent stem cells are the least specialized cells and can give rise to both placental and fetal cells. Pluripotent stem cells can give rise to only fetal cells (all cell lineages from the three germ layers). Multipotent cells are able to differentiate only into the specialized cells of certain tissues and are also found in adults.
Undifferentiated gastrula cells presumed to give rise to neural tissue were transplanted from a donor frog embryo onto an undifferentiated gastrula area of a host frog embryo. The transplantation region in the host was presumed to give rise to epidermal tissue. Both host and donor embryos were allowed to develop following the transplant, and gave rise to two normal embryos. What was the purpose of this experiment?
A) To determine which cells in the gastrula ultimately give rise to epidermal tissue
B) To determine if cell specialization is influenced by communication between cells
C) To determine how developmental fates of cell are determined during blastula formation
D) To determine whether cell differentiation could be reversed based on embryonic location
B
Cell fate is influenced by inductive signaling between cells in the early embryo. In inductive signaling, an inducer (the signaling cell) releases chemical signals that act on competent neighboring cells by regulating the expression of specific genes required for cell determination. The researchers wanted to determine whether the prospective donor neural cells would continue to develop independently into nervous tissue or if they would assume a different tissue type or cell fate due to communication with surrounding cells.
In vertebrates, researchers found that the concentration pattern of the signaling proteins Sonic Hedgehog (Shh) and Bone Morphogenic Protein (BMP) defined by specific regions of expression for various genes involved in neural tube development. The results of their investigation are shown in the graph provided. (Shh increases from 10% to 100% and BMP from 90% to 5%; these trends progress from Dorsal to Ventral on the graph)
A) Shh influences the expression of genes necessary for cell division
B) Shh diffuses along a concentration gradient to signal cell differentiation
C) Shh signals for development of the ventral neural tube only
D) Shh acts as a receptor for BMP in the developing neural tube
B
Morphogens are signaling molecules that influence cell differentiation in the embryo. They are released by signaling cells and diffuse outward to alter gene expression in competent cells in a concentration-dependent manner.
Neural tube defects (NTDs) are thought to be caused in part by folate deficiency. Folate plays a critical role in normal cell division and growth as it is a necessary coenzyme for DNA synthesis and methylation. It has been hypothesized that folate decreases NTD risk by ameliorating oxidative stress, thereby reducing damage to developing cells in the embryo. Compared to newborns without NTDs, a newborn diagnosed with myelomeningocele would most likely have exhibited which of the following during gestation?
A) Lower frequency of cell damage at critical developmental periods
B) Lower cellular concentrations of free radicals
C) Higher levels of antioxidant enzymes
D) Higher incidence of apoptosis
D
Apoptosis (programmed cell death) is crucial for normal embryonic patterning and development. Oxidative stress occurs when the body is unable to detoxify naturally generated reactive oxygen species, which then cause considerable cell damage upon accumulation. This damage can result in abnormal apoptosis and congenital malformations.
The N-terminal domain of angiopoietin-like 4 induces a conformational change in the enzyme lipoprotein lipase (LPL), forcing the LPL homodimer to dissociate into two inactive 225-residue monomers. A scientist studying the sequence of the homodimer of LPL would most likely expect that:
A) 675 mRNA nucleotides must be translated to form a fully functional 50-kDa LPL protein
B) 1,350 mRNA nucleotides must be translated to form a fully functional 50-kDa LPL protein
C) 675 mRNA nucleotides must be translated to form a fully functional 25-kDa LPL protein
D) 1,350 mRNA nucleotides must be translated to form a fully functional 25-kDa LPL protein
B
The total number of nucleotides in an mRNA molecule can be calculated by multiplying the number of amino acids in the protein by the number of nucleotides (three) in a codon. The approximate molecular weight of a protein can be obtained by multiplying the number of amino acids in the protein by the average molecular weight of an amino acid (110 Da).
Codon (3 nucleotides) = 1 amino acid
1 amino acid = 110 Da
225-residue = 225 amino acids x two inactive monomers = 450 AAs
450 x 3 (codon) = 1,350 total nucleotides in the protein
450 AAs x 110 Da per amino acid = 49,500 Da = 49.5 kDa or 50 kDa
Based on the p-values in figure 2, ANGPTL4 mutations were found to decrease coronary artery disease (CAD) risk by significantly altering which of the following? (P values: LDL = 0.06, HDL = 0.087 and Triglycerides = 0.023)
I. LDL cholesterol levels
II. HDL cholesterol levels
III. Triglyceride levels
A) I only
B) III only
C) I and II only
D) II and III only
B
The p-value is the probability of observing a result due to chance alone, assuming that the null hypothesis is true. A value of p being greater than or equal to 0.05 is generally considered statistically significant whereas a value of p being less than 0.05 is not considered statistically significant.
Glucocorticoid deficiency disrupts the negative feedback loop linking the brain to the adrenal gland, leading to hyperplasia (increased cell proliferation) of adrenal tissue. Glucocorticoid deficiency is known to impair healing of superficial wounds, memory formation, and other physiological phenomena. This deficiency most likely leads to these wide-ranging effects because:
A) Glucose is the primary energy source in many of the body’s tissues
B) Receptors for glucocorticoid hormones are expressed in diverse tissue types
C) Glucocorticoids modulate thyroid hormone release by the thyroid gland
D) Hyperplasia of adrenal tissue in CAH causes damage to several nearby organs
B
In glucocorticoid deficiency, an insufficient amount of glucocorticoid hormones in the blood leads to diminished binding of these hormones to their receptors. This condition would compromise the normal function of the various cells that express glucocorticoid receptors. Any cell type that expresses a hormone receptor will respond to serum levels of the hormone, and will have reduced functionality if the serum levels of the hormone decrease (deficiency).
The neuroendocrine signaling cascade that induces adrenal hyperplasia involves coordinated activity among which organs?
A) Hypothalamus, parathyroid glands, adrenal glands
B) Hypothalamus, pituitary gland, adrenal glands
C) Liver, pituitary gland, adrenal glands
D) Pituitary gland, parathyroid glands, adrenal glands
B
The hypothalamus is a brain structure that regulates numerous endocrine functions through its association with the pituitary gland. Together, the hypothalamus and pituitary gland regulate the synthesis and secretion of hormones that influence metabolism, reproduction, and other important functions. Hypothalamus releases corticotrophin-releasing hormone (CRH) which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH) into the blood stream. ACTH then acts on the adrenal glands to promote synthesis and secretion of glucocorticoids (neuroendocrine signaling cascade).
Patient with congenital adrenal hyperplasia (CAH) exhibit hypoglycemia due to numerous endocrine abnormalities. In healthy individuals, hypoglycemia will trigger an increase in the serum level of:
I. Insulin
II. Epinephrine
III. Glucagon
A) I only
B) II only
C) I and III only
D) II and III only
D
Glucose is a key energy source for many tissue in the human body. The serum level of glucose is tightly regulated through the actions of the hormones insulin, glucagon, epinephrine, norepinephrine, and the glucocorticoids. Insulin decreases blood glucose concentration by promoting the cellular uptake and storage of glucose; insulin levels will go down as blood glucose goes down.
Normally, 21-hydroxylase catalyzes chemical reactions involved in the synthesis of aldosterone and cortisol, the principal mineralocorticoid and glucocorticoid hormones, respectively. As a results, patients with 21-hydroxylase deficiency (congenital adrenal hyperplasia) exhibit diminished serum levels of aldosterone and cortisol. What changes in blood volume and serum sodium content would be expected as a result of using synthetic hormones to replenish aldosterone in congenital adrenal hyerplasia (CAH) patients?
A) Increased blood volume and increased serum sodium content
B) Increased blood volume and decreased serum sodium content
C) Decreased blood volume and increased serum sodium content
D) Decreased blood volume and decreased serum sodium content
A
Patients with congenital adrenal hyperplasia (CAH) exhibit deficient synthesis and secretion of aldosterone. After administering synthetic aldosterone, increased sodium and water reabsorption by the kidneys will result in increased blood volume and increased serum sodium content.
More than 90% of congenital adrenal hyperplasia (CAH) diagnoses are associated with a deficiency of 21-hydroxylase, an enzyme encoded by the CYP21A2 gene on chromosome 6. Given that the fusion of male and female gametes results in fertilization, which statement best explains how unequal crossing over during gametogenesis can lead to 21-hydroxylase deficiency in the fertilized embryo? One of the parental gametes:
A) Contained an extra copy of chromosome 6
B) Contained no copies of chromosome 6
C) Underwent an event in which the CYP21A2 gene was duplicated
D) Underwent an event in which the CYP21A2 gene was deleted
D
Crossing over is a form of genetic recombination involving the exchange of genetic material between non-sister chromatids of homologous chromosomes. Unequal crossing over can result in offspring that lack important genes. If unequal crossing over involving chromosome 6 occurs, it may result in a daughter cell that contains a chromosome lacking CYP21A2, which would contribute to the development of 21-hydroxylass deficiency in offspring (not increasing it).
Which statement best describes the characteristics of hormones secreted from the pituitary gland?
A) Hormones secreted from the posterior pituitary are synthesized in the hypothalamus
B) Hormones secreted from the posterior pituitary act on other endocrine glands
C) Hormones secreted from the anterior pituitary only act directly on nonendocrine tissues
D) Hormones secreted from the anterior pituitary are released by depolarization of the nerve terminals
B
The synthesis and secretion of hormones from the anterior pituitary is regulated by the release of neurohormones into the blood from neurons located in the hypothalamus. In contrast, posterior pituitary hormones are synthesized in hypothalamic neurons and undergo anterograde axonal transport to the posterior pituitary. The secretion of stored posterior pituitary hormones from the axon terminals is mediated by depolarization of the nerve terminals.
Human cardiac muscle differs from skeletal muscles because it:
A) Appears striated
B) Requires acetylcholine to contract
C) Contained intercalated discs
D) Contains cells with multiple nuclei
C
Muscle tissue can classified as cardiac, skeletal, or smooth. Cardiac muscle is striated and under involuntary control. Skeletal muscle is striated and under voluntary control, and smooth muscle is not striated and under involuntary control. Cardiac muscle is unique in that each cell is connected to adjacent cells via intercalated discs, which are regions of cell contact that contain both desmosomes (to prevent cells from separating during contraction) and gap junctions (to facilitate direct ion exchange for synchronized contraction).
During muscle contraction, the power stroke is the pivoting motion of the myosin head that pulls the actin filament inward to shorten the sarcomere. Given this, which of the following events immediately precedes the power stroke?
A) The binding of ATP to the myosin heads
B) The hydrolysis of myosin-bound ATP to ADP and Pi
C) The release of ADP and Pi from the myosin head
D) The binding of Ca2+ to tropomyosin
C
When ATP bound to a myosin head hydrolyzes, the myosin head shifts back and attaches to the actin filament. Dissociation of ADP and Pi leads to a power stroke, which shortens the sarcomere. A new ATP molecule binds to the myosin head, causing it to dissociate from the actin filament. The action of many myosin heads cycling through this process leads to muscle contraction.
A scientist claims that endurance training is an exercise method that can improve physical performance by inducing changes in type 1 skeletal muscle fibers that allow the fiber to perform aerobic respiration more efficiently to generate ATP. Given this, which of the following adaptations is most likely to occur in type 1 fibers in response to endurance training?
I. Mitochondrial density of the muscle fibers increases
II. Capillary supply around the muscle fiber increases
III. Myoglobin concentration per muscle fiber increases
A) I only
B) I and II only
C) III only
D) I, II, and III
D
Skeletal muscle fibers can be classified as type 1 (slow oxidative), 2A (fast oxidative-glycolytic), or 2X (fast glycolytic). The speed of contraction (slow or fast) is determined by the catalytic speed of the myosin ATPase and the activity of the fiber’s associated motor neuron. Oxidative fibers are fatigue resistant and synthesize ATP through aerobic respiration (oxygen-requiring pathways). Glycolytic fibers are easily fatigable and generate ATP through anaerobic glycolysis (in absence of oxygen).
It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. The cheetahs that survived the environmental catastrophe that occurred 12,000 years ago are at a greater risk of extinction because of:
A) Naturally selected changes in allele frequencies
B) Random changes in allele frequencies
C) Changes in allele frequencies due to migration
D) Changes in allele frequencies due to random mating
B
Genetic drift is a mechanism of evolution; however, unlike natural selection, the variations in allele frequencies occur randomly by chance. Because smaller populations have a smaller gene pool, the random (good or bad) variations due to genetic drift cannot be buffered. The smaller the population, the less likely it will have the ability to negate any adverse impact that random changes in allele frequency which may lead to extinction.
Assume that a subgroup of Namibian cheetahs exclusively hunt prey that weigh more than 100 kg. The individuals that make up this subgroup possess larger claws and teeth compared to average Namibian cheetahs and retain the ability to naturally mate with them. These morphological and behavioral changes reflect:
A) The selection of average over extreme phenotypes
B) How extreme characteristics are favored over average ones
C) Diversification of characteristics to better fill an ecological niche
D) A new species
C
Adaptive radiation is the process of diversifying characteristics (claw and teeth size) to better fill an ecological niche. Adaptive radiation can eventually lead to speciation if the subgroup continues to diverge and loses the ability to interbreed with individuals from the original species.
Researchers concluded that captive cheetahs have reduced fitness because of their increased susceptibility to diseases. They reached this conclusion based on results of two separate graphs, one in which it showed that for Liver, GI and Kidney disease, captive cheetahs were more affected overall than wild cheetahs. The second graph showed a significant increase in the amount of cortisol in the feces of captive cheetahs. What can best explain the decreased fitness of captive cheetahs?
A) Increased MHC diversity
B) Decreased MHC diversity
C) Increased environmental stress
D) Decreased environmental stress
C
MHC are cell surface receptors in vertebrates that present foreign molecules in order to elicit an immune response. MHC variations are evolutionarily important to an organism’s fitness because they influence the organism’s ability to combat a variety of infections and diseases. It can be concluded that other factors besides genetics determine the fitness of captive male cheetahs. The decreased fitness can be attributed to increased cortisol levels in captive cheetah fecal matter. Cortisol is a marker for increased environmental stress.
It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. Over time, the offspring of subsequent generations exhibited decreased fitness, reduced fecundity (number of offspring), and sustained a loss of major histocompatibility complex (MHC) allele diversity. If wild Namibian cheetahs continue breeding as described in the passage, what is most likely to occur to their population size in the long term?
A) Increased population size with equal sex ratio
B) A sharp increase followed by a slight decrease in population size
C) Elimination of the Namibian cheetah species
D) Stable population size consisting of mostly females
C
Inbreeding depression is characterized by decreased genetic diversity, reduced fecundity, and decreased fitness. As genetic diversity decreases within a population, the frequency of homozygous deleterious recessive-genes increases within that population. Consequently, inbred populations have an increased probability of becoming extinct.
Compared to the blood flowing into the left ventricle, the blood flowing into the right ventricle:
A) Has a higher oxygen concentration
B) Has a higher pH
C) Is passing through a cardiac chamber with thinner walls
D) Is passing through a cardiac chamber that contracts to produce higher pressure
C
The right ventricle has thinner walls than the left ventricle because it needs to pump blood at a lower pressure to reach only the lungs. In contrast, the thicker walls of the left ventricle allow it to pump blood at a higher pressure to reach all other tissues in the body.
The DNA telomeres can be most accurately described as:
A) Noncoding and highly repetitive
B) Single-stranded and self-complementing
C) Able to encode multiple unique proteins
D) Easily cleaved by restriction enzymes
A
Telomeres are highly repetitive stretches of DNA at the ends of a chromosome. They are shortened by each round of DNA replication, and protect the rest of the chromosome from degradation. Because of this, telomeres do not encode any gene products; if they did, the information for those products would be lost upon replication and could harm the cell.
In neurons, action potential propagation occurs along the axon. The analogous structure in skeletal muscle fibers that enables action potential propagation is the:
A) Actin filament
B) Transverse (T) tubule
C) Motor endplate
D) Myelin sheath
B
Electrical depolarization caused by action potential propagation leads to the contraction of skeletal muscle fibers. As extensions of the plasma membrane that penetrate deep into muscle fibers, transverse (T) tubules are specialized muscle fiber structures that facilitate action potential propagation throughout individual muscle fibers.
Researchers are studying a single-celled pathogen. Which experimental method would be LEAST effective for determining whether the pathogen is prokaryotic or eukaryotic?
A) Analyzing the cells for the number of origins of replication
B) Exposing the pathogen to a fluorescent antimitochondrial antibody
C) Testing the pathogen for ribosome size
D) Assessing the pathogen for the presence of pyruvate in the cytoplasm
D
Eukaryotic cells contain membrane-bound organelles and linear genomes with multiple origins of replication. In contrast, prokaryotic cells lack membrane-bound organelles and have circular genomes with a single origin of replication. However, both cells have ribosomes (80S in eukaryotes and 70S in prokaryotes) and can perform glycolysis. Glycolysis is a process that occurs in the cytoplasm of both cells types and results in the synthesis of pyruvate. Thus, the presence of pyruvate is not an effective method to distinguish between prokaryotes and eukaryotes.
Viral genomes (RNA and DNA) are enclosed by a protein shell known as the capsid. Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid. Viruses that lack this outermost phospholipid covering are labeled non-enveloped. Fluorescent antibodies, designed to bind the capsid proteins of the five hepatitis viruses, were added to separate wells containing each type of virus. The fluorescence assay that was performed detected only bound antibodies in media with HAV or HEV. Based on the information, which of the following viruses does NOT have an outer phospholipid bilayer?
A) HBV
B) HCV
C) HAV
D) HDV
C
All viruses contain a protective protein coat known as the capsid. Viruses that contain only a capsid as an outer layer are known as non-enveloped or naked viruses, and are able to survive in harsh conditions. Viruses with a phospholipid bilayer surrounding the viral capsid are referred to as enveloped viruses; these are more susceptible to changes in environmental conditions. Because the antibodies were able to bind directly to the capsid proteins of both viruses, it can be determined that both HAV and HEV are non-enveloped viruses.
An example of an infectious disease is viral hepatitis (inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A-E) that infect hepatocytes (liver cells). HAV, HCV, AND HEV contain positive-sense, single-stranded RNA (+ssRNA) as genetic material. In contrast, HBV has a partially double-stranded circular DNA genome. HDV is unique because it has a negative-sense, single-stranded RNA (-ssRNA) genome. Researchers perform an experiment in which they infect wild-type mice with either HBV or HEV and subsequently treat them with a drug that inhibits their cellular RNA polymerase activity. Based on this information, administering this drug to mice infected with either HBV or HEV would result in:
I. Decreased viral load in HBV-infected mice
II. Decreased viral load in HEV-infected mice
III. Reduced number of viral fragments displayed by antigen-presenting cells in HBV-infected mice
A) I and II only
B) I and III only
C) II and III only
D) I, II, and III only
B
Most double-stranded DNA viruses utilize host machinery and resources to transcribe positive-sense mRNA from viral DNA. Positive-sense ssRNA viruses (except retroviruses) replicate their genomes by encoding their own viral RNA-dependent RNA polymerase. The administered compounds inhibit only the host’s DNA-dependent RNA polymerase activity. The viral polymerase translated from the HEV genome will continue to replicate its viral genome by creating a complementary negative-sense mRNA intermediate.
An individual with hepatitis is suspected to have been exposed to either a bacterial strain of Bartonella henselae (0.5 micrometers) or HCV (0.055 micrometers). Healthy hepatocytes and hepatocytes infected with serum from the affected patient were grown on chamber slides separated by double membranes. (Diagram shows membrane between chambers 1 and 2 as well as 2 and 3. Membrane between 1 and 2 has a pore size of 4 micrometers and the other membrane has a pore size of 0.2 micrometers).
A cellular morphology similar to infected hepatocytes was observed in both chambers 2 and 3 after a 6 hour incubation time. Using a light microscope, can investigators observe the agent that caused the patient’s hepatitis in chamber 3?
A) Yes, because it was caused by HCV
B) Yes, because it was caused by B. henselae
C) No, because it was caused by HCV
D) No, because it was caused by B. henselae
C
A light microscope has a resolution of 200 nm (0.2 micrometers); consequently, investigators can use it only to observe cells larger than 0.2 micrometers. For viruses such as HCV, which are 100 times smaller than bacteria and 1,000 times smaller than eukaryotic cells, visual observations require greater resolution. As a result of the 0.2 micrometer pore size leading into chamber 3 and the low resolution of the instrument, investigators will be unable to observe the causative agent of the hepatitis visually using a light microscope
Physicians researching a global hepatitis outbreak discover a new strain of hepatitis (HXV) by analyzing chromosomal DNA of patient’s liver cells. They found that HXV has a +ssRNA genome and replicates through DNA intermediates. What characteristic best describes the new hepatitis virus?
A) It integrates its retroviral +ssRNA into the host genome
B) It has reverse transcriptase function
C) It synthesizes a complementary strand
D) It translates its own proteins
B
The newly discovered hepatitis strain, HXV, was identified while analyzing chromosomal DNA of liver (host) cells. This indicates that the virus is a retrovirus because it integrated with the host genome (DNA). Retroviruses are unique in that they are enveloped and carry two identical +ssRNA molecules. RNA viruses such as HXV must convert their genomes (+ssRNA) into double-stranded DNA (dsDNA) using reverse transcriptase (RNA-dependent DNA polymerase activity) before integration into the host genome can occur.
Assume bacteria are infected with a vector containing hepatitis B (HBV) genetic material. This vector has been shown to introduce its genomic content into bacterial cells without fully gaining entry into the bacterial cytoplasm. Based on this information, the vector is most likely a:
A)Prion
B) Bacterium
C) Viroid
D) Bacteriophage
D
Bacteriophages are viruses that exclusively infect bacterial cells. They contain tail fibers that allow them to recognize and attach to the cell membrane, and a tail sheath that injects the viral genome into the bacterium. Viroids and prions are considered subviral particles because they are smaller in size and complexity compared to viruses.
A student analyzing actively dividing cells under the microscope finds that each daughter cell contains half the number of chromosomes as the parent cell. Given this, these cells most likely contain all of the following EXCEPT:
A) Peroxisomes
B) Nuclear pore proteins
C) Single-stranded genomic material
D) Microtubules
C
Eukaryotic cells can be distinguished by their unique characteristics. For example, they have a genome with multiple linear chromosomes (double-stranded DNA), they use meiosis as one mechanism of cell division (sexual reproduction), and they have membrane-bound organelles. Half the number of chromosomes in the parent cell = 1n or meiosis. Single-stranded found in certain viruses
Plasmodium falciparum is a protozoan parasite known to cause malaria, an illness characterized by fever, chills, and flu-like symptoms. Which of the following is the most likely reason why P. falciparum would be classified as a eukaryotic organism?
A) It is able to reproduce sexually
B) It has a mechanism for intron splicing
C) It has a cell wall
D) It has a cell membrane
B
Protozoa are single-celled eukaryotic organisms, and therefore possess all of the unique characteristics of eukaryotic cells, including a mechanism for splicing introns from mRNA in the nucleus. Eukaryotic and prokaryotic cells are similar in that both have mechanisms of sexual reproduction and are enclosed by a plasma membrane. In addition, all prokaryotes and some eukaryotes have cell walls.
Researchers analyzing gene expression in connective tissue samples are likely to obtain gene expression profiles for all of the following tissues EXCEPT:
A) Bone tissue
B) Blood tissue
C) Adipose tissue
D) Muscle tissue
D
The body consists of four types of tissue: epithelial (skin, lining of hollow organs and digestive tract), muscle (skeletal, cardiac and smooth), connective (bone, blood, adipose, tendons/ligament and cartilage), and nervous tissue (brain, spinal cord and nerves). Connective tissue provides protection and support for organs.
A pathogen identified in a patient’s blood sample is found to lack a phospholipid bilayer. Therefore, any medications used to treat the disease caused by this pathogen would most likely be classified as:
A) Anti-protozoan drugs
B) Anti-fungal drugs
C) Anti-viral drugs
D) Anti-bacteria drugs
C
Viruses posses DNA or RNA genomes surrounded by a protein capsid and are unable to reproduce outside of a host. Viruses can also be classified as either enveloped (have a phospholipid bilayer as the cell membrane) or non-enveloped (no phospholipid bilayer). In contrast, all prokaryotic and eukaryotic cells are enclosed by a phospholipid bilayer.
Excretion of glucose in the urine (glycosuria) occurs when the glomerular filtration rate (GFR) exceeds the transport maximum of glucose (Tm). First, researchers measured the participants’ fasting serum glucose levels (average ~80 mg/dL) and then began a continuous intravenous infusion of a glucose solution. The rate of glucose infusion was adjusted such that blood glucose concentration steadily rose to 300mg/dL. The experiment was later repeated in the same patients following canagliflozin administration (100 mg, once a day for seven days).
The critical concentration of plasma glucose necessary to induce glycosuria is termed the renal threshold of glucose. Compared to untreated T2DM patients, the renal threshold of glucose in T2DM patients treated with canagliflozin is:
A) Higher by approximately 75 mg/dL
B) Higher by approximately 175 mg/dL
C) Lower by approximately 115 mg/dL
D) Lower by approximately 300 mg/dL
C
Urine glucose excretion is a crude definition for glycosuria. The provided graph (not shown) depicted a graph that showed Canagliflozin began excreting glucose from the urine around 75 mg/dL and the untreated patients were at 200 mg/dL. A threshold is a set of values that must be surpassed for a particular event to take place.
Researchers hypothesized that administration of canagliflozin reduces blood pressure in patients with diabetes by increasing urine output and reducing total blood volume. A decrease in which of the following would also result in lowered blood pressure?
I. Activation of the renin-angiotensin system
II. Production of aldosterone
III. Secretion of antidiuretic hormone
A) II only
B) III only
C) I and III only
D) I, II, and III
D
Hormones such as angiotensin II, aldosterone, and antidiuretic hormone (ADH; vasopressin) regulate blood pressure by modulating the kidney’s reabsorption of water and salts. The renin-angiotensin system (RAS) ultimately raises blood pressure by including both the release of aldosterone from the adrenal cortex and the constriction of arterioles. Aldosterone acts on the distal tubules and collecting ducts to promote reabsorption of Na+ and the secretion of K+. ADH promotes water reabsorption by increasing permeability of the distal tubule and collecting ducts to water. ADH induces vasoconstriction and narrowing of the blood vessels.
Urinary retention in patients with poorly controlled diabetes mellitus is most likely the result of nerve damage impairing smooth muscle contraction in which of the following structures?
A) Bladder
B) Urethral sphincters
C) Kidney
D) Ureter
A
Urination is controlled by musculature lining the urinary tract. Nerve damage that impairs the contraction if the detrusor muscle of the bladder would impair emptying of the bladder and lead to urinary retention. During urine collection, the detrusor muscle is relaxed; the internal and external urethral sphincters are contracted to prevent urine flow down the urethra.
Canagliflozin is a sodium-glucose linked transporter (SGLTs) inhibitor, used for the treatment of diabetes mellitus. SGLTs are secondary active transport proteins located in the apical membrane of the proximal tubular cells in the kidney. Their activity determines the transport maximum of glucose Tm, the maximum rate at which the kidneys can reabsorb glucose.
Administration of canagliflozin most directly increases urinary output by increasing the:
A) Osmotic pressure of the tubular filtrate
B) Osmotic pressure of the peritubular capillaries
C) Hydrostatic pressure of the renal artery
D) Hydrostatic pressure of Bowman’s space
A
SGLTs transport glucose out of the proximal tubule so it can be returned to circulation through the peritubular capillaries. Administration of a SGLT inhibitor prevents glucose reabsorption, increasing solute concentration within the tubule and consequently increasing the osmotic pressure of the tubular filtrate. As a result, water is drawn back into the renal tubule, increasing urine output. The kidneys regulate blood osmolarity, and in turn blood pressure, by selectively modulating the reabsorption and secretion of water and solutes.
Sodium-glucose linked transporters (SGLTs) transport glucose against its concentration gradient across the luminal membrane of the proximal tubule. The energy to drive this form of glucose transport is most likely directly provided by:
A) An electrochemical Na+ gradient
B) An action potential
C) ATP hydrolysis
D) Simple diffusion of Na+ ions
A
SGLTs are secondary active transport proteins. This means that they utilize the energy released by the movement of Na+ along its concentration gradient to move glucose against its concentration gradient. The movement of Na+ along its concentration gradient enables glucose reabsorption. Primary active transport utilizes the energy from ATP hydrolysis to move a substance against its concentration gradient. Secondary utilizes the energy released by passive transport of another molecule.
In individuals with glycosuria, glucose that is not reabsorbed in the proximal tubule next flows into which of the following nephron structures?
A) The distal tubule
B) The collecting duct
C) The loop of Henle
D) Bowman’s capsule
C
Fluid that is filtered by the kidney first enters the Bowman’s capsule before passing into a long tubule, where water and solutes are selectively reabsorbed. Wastes and metabolites are excreted as urine. The segments are in the order of proximal tubule, the loop of Henle, distal tubule and finally the collecting duct.
Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis. Specifically, PTH functions to increase plasma calcium concentration and reduce plasma phosphate levels. Secondary hyperparathyroidism is a condition characterised by excessive PTH release in response to depressed serum calcium or elevated serum phosphate levels.
Which of the following is a potential complication of secondary hyperparathyroidism?
A) Decreased bone mineralization
B) Decreased osteoclast activity
C) Increased osteoblast activity
D) Increased corticol bone mass
A
The net effect of parathyroid hormone (PTH) activity is to increase serum calcium and decrease serum phosphate concentration. PTH secretion from the parathyroid gland is triggered by decreased plasma calcium. PTH indirectly stimulates osteoclast activation, promoting bone breakdown and the release of ionic calcium into the blood. PTH ultimately triggers osteoclast activity, which results in decreased bone mineralized as osteoclasts resorb bone material.
Parathyroid hormone (PTH) functions to increase plasma calcium concentration and reduce plasma phosphate levels. Secondary hyperparathyroidism is a condition characterized by excessive PTH release in response to depressed serum calcium or elevated serum phosphate levels.
Secondary hyperthyroidism may result from:
I. Increased intestinal calcium absorption
II. Impaired renal phosphate reabsorption
III. Deficient renal calcitriol synthesis
A) I only
B) III only
C) I and II only
D) I, II, and III
B
PTH increases the activity of the enzyme that catalyzes the final step in the conversion of inactive circulating vitamin D into the active form, calcitriol. Increased intestinal absorption of calcium will raise blood calcium levels, which will serve as a negative feedback signal to end PTH secretion. If phosphate cannot be properly reabsorbed in the kidney, it will be excreted in urine, and free calcium ions in the blood will increase.
Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis. Specifically, PTH functions to increase plasma calcium concentration and reduce plasma phosphate levels.
Researchers treated mice with regular intraperitoneal infusions of CaCl2 to cause a sustained increase in serum calcium levels. The hormone that was released as a result of this condition was monitored using a hormone-specific radiolabeled antibody. In the tested animals, what organ would most likely show increased binding of radiolabeled antibody?
A) Thymus
B) Pancreas
C) Bone marrow
D) Thyroid
D
In response to increased plasma calcium concentration, the peptide hormone calcitonin is secreted by the thyroid glands. Calcitonin mainly acts to reduce plasma calcium by decreasing osteoclast activity (bone resorption) and increasing renal excretion of calcium.
Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. The progressive breakdown of articular cartilage ultimately results in complete exposure of the corticol portion of the underlying subchondral bone with narrowing of the joint space. Repeated and abnormal joint stress can also cause the development of osteophytes, or bony growths, that form on the subchondral bone.
OA commonly affects large, weight-bearing joints of the lower extremities such as the knee and hip. Based on the passage, which of the following would occur in a patient with OA involving the knees?
A) Deterioration of the yellow bone marrow in affect bones
B) Deposition of excess bone on the epiphysis of affected long bones
C) Reduction of hematopoiesis in the red marrow of affected bones
D) Degeneration of compact bone at the diaphysis of affected long bones
B
The structure of a long bone includes the epiphysis (rounded ends covered by articular cartilage), the diaphysis (shaft containing the medullary cavity filled with yellow bone marrow), and the metaphysis (where the diaphysis and epiphysis meet).
Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints.
Osteoporosis, a disease marked by decreased bone density and mass, is similar to OA in that it is a degenerative bone disorder correlated with old age. Which two skeletal system functions would OA and osteoporosis impair, respectively?
A) Mobility and structural support
B) Mobility and leukocyte production
C) Calcium storage and structural support
D) Calcium storage and leukocyte production
A
The skeletal system facilitates mobility, provides the body with structural support, is the site of hematopoiesis, protects the body’s internal organs, and serves to store fat, calcium, and phosphate. No research suggests that osteoporosis affects the red bone marrow’s ability to production red and white (leukocytes) blood cells.
Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints.
Microscopic examination of tissue samples obtained from the type of bone that becomes exposed to advanced OA is most likely to reveal all of the following EXCEPT:
A) Volkmann canals connecting haversian canals
B) Mature chondrocytes
C) Canaliculi
D) Osteocytes situated within lacunae
B
Compact bone is organized into concentric rings of bone matrix called lamellae. The entire unit of concentrically arranged lamellae surrounding a central haversian canal is known as an osteon, or haversian system. Within each osteon, lacunae (spaces containing osteocytes) connect to one another via microscopic channels called canaliculi, which allow osteocyte waste exchange and nutrient delivery. Chondrocytes make up the cellular component of cartilage, not bone.
Which of the following statements is NOT true about hyaline cartilage?
A) It lacks innervation
B) It gives rise to bone through endochondral ossification
C) It serves as an attachment that holds bones to muscle
D) It is avascular and receives nutrients from surrounding fluids
C
Cartilage is a firm but flexible connective tissue that lacks blood veseels and nerves. Chondrocytes (cartilage cells) secrete chondrin, which is specialized extracellular matrix that makes up cartilage. The most common type of cartilage is hyaline cartilage, which plays a role in bone development and lines the ends of articulating bones. Tendons, specifically, tautly anchor muscle to bone, not hyaline cartilage.
Which organ synthesizes a compound that facilitates the mechanical digestion of lipids?
A) Pancreas
B) Salivary glands
C) Gallbladder
D) Liver
D
Bile is synthesized in the liver, stored in the gallbladder, and released into the duodenum to aid lipid digestion. Bile salts, a key component of bile, mechanically digest lipid globules by physically breaking them down into smaller droplets in a process known as emulsification. Subsequently, pancreatic lipase chemically digests emulsified lipids.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are weakly acidic compounds that normally pass through the acidic environment of the stomach in a nonionized form until they reach the small intestine, where they become ionized in the less acidic lumen. Ionized NSAIDs are more soluble and therefore dissolve faster. (Ionized NSAIDs just have a H+ removed from the OH group).
Would NSAID solubility in the gastric pouch of postoperative RYGB patients be higher than normal?
A) No, because RYGB decreases the pH of gastric juice
B) No, because RYGB increases the pH of gastric juice
C) Yes, because RYGB increases the pH of gastric juice
D) Yes, because RYGB decreases the pH of gastric juice
C
The acidic pH of the stomach is maintained by gastric juice, which is primarily composed of hydrochloric acid (HCL). This acidic environment is required for protein digestion and to kill harmful bacteria. When gastric juice mixed with food (chyme) enters the duodenum, it is neutralized by bicarbonate ions (from the pancreas) and bile (released from storage in the gallbladder). The small gastric pouch surgically created contains less parietal cells and consequently, the amount of HCL secreted by these cells is reduced. Parietal cells are found strictly in the stomach and less cells means high pH; more soluble is less acidic environments.
Roux-en-Y gastric bypass (RYGB) is a highly effective weight loss interventional surgery that facilitates massive and immediate weight loss. The stomach is divided into a small pouch and reverted to bypass everything from the gastric pouch to the upper duodenum; filling into the lower duodenum directly from the gastric pouch.
In RYGB patients, ingested food will NOT pass through the:
A) Cardiac sphincter
B) Intestinal villi
C) Pyloric sphincter
D) Cecum
C
At certain sections along the gastrointestinal tract, sphincters, or rings of muscle, divide the tract into segments with distinct functions. Ingested food passes from the esophagus into the stomach through the cardiac sphincter, and from the stomach into the duodenum through the pyloric sphincter. If reverted from the cardiac sphincter to the lower duodenum, then the only structure not passed through is the pyloric sphincter.
Roux-en-Y gastric bypass (RYGB) is a interventional procedure designed to facilitate massive and immediate weight loss by diverting the alimentary canal; by passing stomach to upper duodenum. Researchers have found that transplanting gut microbiota of obese postoperative RYGB mice inti nonoperated, obese mice lacking gut flora may reproduce the therapeutic effects of RYGB in transplant-recipient mice.
Obese mice underwent either RYGB or sham (placebo) surgery, and two weeks post-surgery, their fecal matter was transplanted into the guts of nonoperated, obese mice lacking gut flora (germ-free recipients). The body weight of RYGB flora recipients (RYGB-R) and sham surgery flora recipients (SHAM-R) was measure for 3 weeks postcolonization. Which graphic shows the expected results of this experiment?
A) RYGB-R decreases in % body weight, SHAM-R stays level
B) RYGB-R increases in % body weight, SHAM-R stays level
C) RYGB-R stays level, SHAM-R decreases in % body weight
D) RYGB-R stays level, SHAM-R increases in % body weight
A
Research suggests that restructuring the composition of gut flora can influence body weight. The human gut generally contains nonpathogenic bacterial flora that symbiotically cohabit with enterocytes. These microorganisms produce vitamins (vitamin K, necessary for clotting) and aid with nutrient and drug metabolism.
Roux-en-Y gastric bypass (RYGB) is a surgical procedure designed to restructure the alimentary canal and promote massive, immediate weight low. The new tract bypasses the stomach to upper duodenum; anything in between these areas are not visited when bypassed through the new alimentary limb.
All of the following are secreted by cells in the alimentary limb of RYGB patients EXCEPT:
A) Pepsinogen
B) Trypsinogen
C) Gastrin
D) Mucus
B
The pancreas generally secretes proteolytic enzymes, like trypsinogen, into the pancreatic duct, which empties into the duodenum to aid in the digestion of chyme in the lumen. In RYGB patients, pancreatic trypsinogen is released into the biliopancreatic limb, NOT the alimentary limb. The cells in the stomach secrete the following: gastrin (from G cells) signals parietal cells to secrete HCl (from parietal cells); pepsinogen (from chief cells) cleaves polypeptides when activated by HCl; and mucus (from mucous cells) and bicarbonate (from epithelial cells) protect the stomach lining against autodigestion by gastric juice.
A staple leak is an unanticipated opening of surgical staples at an incision. In RYGB, a staple line leak at the junction of the biliopancreatic limb and the alimentary limb would cause gastrointestinal tract contents to enter:
A) The perineum
B) The peritoneum
C) The peritoneal cavity
D) The pleural cavity
C
The peritoneum is composed of two membranes that line the abdomen: the parietal layer, which lines the abdominal wall, and the visceral layer, which cover the abdominal organs. The peritoneal cavity is a potential space between the parietal and visceral layers of the peritoneum. Perineum is the space between the anus and scrotum (or vulva). The pleural cavity is a fluid-filled space between the membranes of the lungs and would not be affected by leaking GI tract contents.
All of the following findings in sperm would cause lower fertilization rates in IVF EXCEPT:
A) Defects in microtubule structure
B) Mitochondrial deficiency
C) Cytoplasmic reduction
D) Misfolded acrosomal enzymes
C
A human sperm cell is composed of a head (contains the acrosome and nucleus), a midpiece (contains mitochondria that generate the ATP required for flagellum-driven sperm motility), and a tail (ie, the flagellum necessary for motility through a fluid environment). Fully developed sperm generally have little to nonexistent cytoplasm; therefore, reporting that the cytoplasm is reduced in sperm used for IVF would be a normal finding that is unlikely to impact fertilization rate.
If a man and a woman are having difficulty conceiving a child and decide to undergo ICSI treatment using their own gametes, which of the following represents the proper development pathway of the sperm cell selected to fertilize the egg during this procedure?
A) Spermatogonium, spermatocyte, spermatid, spermatozoon
B) Spermatogonium, spermatid, spermatozoon, spermatocyte
C) Spermatocyte, spermatogonium, spermatozoon, spermatid
D) Spermatocyte, spermatid, spermatozoon, spermatogonium
A
Spermatogenesis is process in which male gametes (sperm) are produced and occurs in the seminiferous tubules of the testes. Spermatogonia undergo meiotic division and become spermatocytes, which then become spermatids when meiosis is completed. Spermatids then mature into spermatozoa (mature sperm) through a series of morphological changes.
The North American flying squirrel and the Draco lizard of Southeast Asia both evolved a membrane between their limbs that allows them to glide between trees in their habitats. Given that the species are distantly related, which of the following patterns of evolution would explain the development of this anatomical structure in both organisms?
I. Parallel evolution
II. Divergent evolution
III. Convergent evolution
A) I only
B) II only
C) III only
D) I and II only
C
Convergent evolution leads to similar characteristics in distantly related species that are exposed to similar environmental pressures. Parallel evolution also leads to similar characteristics but occurs in species with a more recent common ancestor. Divergent evolution leads to unique characteristics on somewhat closely related species that face contrasting environmental pressures.
Given that a species diverged from its ancestor 80 million years ago, which of the following graphs most likely illustrates the pattern of mutation accumulation in the genome of the species over time?
A) Graph depicts negative linear slope
B) Graph depicts horizontal linear line
C) Graph depicts positive linear slope
D) Graph depicts positive, then negative linear slopes
C
Most genetic mutations are neutral and accumulate at a fairly constant rate across organisms over evolutionary time. The overall number of mutations in a species will therefore increase linearly across time. By analyzing the rate of neutral mutations in the genome, this “molecular clock” of evolution can be used to measure evolutionary time and estimate the evolutionary relationships between species.
The diagram below shows the results of a northern blot analysis that tested for the expression of four peptide hormones in two endocrine tissue.
Tissue A: Insulin = yes, Growth hormone = no, Glucagon = yes, Luteinizing = no
Tissue B: Insulin = no, Growth hormone = yes, Glucagon = no, Luteinizing = yes
A. Pituitary gland and pancreas, respectively
B) Pancreas and pituitary gland, respectively
C) Adrenal glands and hypothalamus, respectively
D) Hypothalamus and adrenal glands, respectively
B
Endocrine glands modulate physiological activity via the secretion of hormones. For example, the pancreas secretes insulin and glucagon to regulate blood glucose levels. In contrast, the anterior lobe of the pituitary gland secretes multiple hormones that regulate several processes, including metabolism and reproductive function.
As the two anatomical divisions of the adrenal gland, the adrenal cortex and adrenal medulla share a common feature in that both:
A) Synthesize steroid hormones
B) Release signaling molecules into lymph vessels
C) Regulate the synthesis of red blood cells
D) Secrete hormones that alter blood pressure
D
Each adrenal gland is composed of two anatomically distinct regions: the adrenal medulla and the adrenal cortex. Both regions secrete hormones that regulate blood pressure and allow the body to respond to stressors. Aldosterone, secreted from the adrenal cortex, stimulates Na+ reabsorption in the kidneys (increased water intake and increased blood pressure). Norepinephrine and epinephrine work under extreme stress and promote rapid information processing by maximizing blood flow to organs essential for survival (secreted by adrenal medulla).
The sequence below is a portion of exon 7 of SMN1 of mRNA transcript.
5’ - UCAAGUGAUUCUCCU - 3’
Which of the following represents the corresponding DNA coding strand sequence for this particular transcript?
A) 5’ - AGGAGAATCACTTGA - 3’
B) 5’ - TCCTCTTAGTGAACT - 3’
C) 5’ - AGTTCACTAAGAGGA - 3’
D) 5’ - TCAAGTGATTCTCCT - 3’
D
In transcription, RNA polymerase reads the noncoding DNA strand to produce a complementary mRNA transcript (with uracil replacing thymine). The sequence of the mRNA transcript is identical to the sequence of the coding DNA (again, with uracil rather than thymine).
What steps are required to produce a mature FL-SMN transcript?
I. Excision of noncoding sequences between the 3’ and 5’ untranslated regions in pre-mRNA
II. Addition of multiple adenine nucleotides to the 3’ end of SMN1 pre-mRNA
III. Removal of the 7-methylguanosine cap from mature mRNA
IV. DNA polymerase binding to the SMN1 gene
A) I and II only
B) III and IV only
C) I, II, and IV only
D) I, II, III, and IV
A
Transcription is the process of synthesizing RNA from template DNA and begins with RNA polymerase II binding to the gene promoter region. RNA polymerase II reads the DNA strand in a 3’ to 5’ direction to generate a 5’ to 3’ pre-mRNA molecule. The pre-mRNA transcript undergoes 5’ capping (7-methylguanosine), the addition of a 3’ poly-A tail, and excision of noncoding regions (introns) to be converted into mature mRNA.
Valproic acid (VA) is a histone deacetylase inhibitor that has been investigated for SMA therapy. Valproic acid most likely improves motor neuron survival by:
A) Increasing SMN2 expression by making DNA more accesible
B) Increasing SMN2 expression by removing acetyl groups from histones
C) Decreasing SMN2 expression by modifying CpG sites in DNA
D) Decreasing SMN2 expression by inducing heterochromatin formation
A
Heterochromatin, or tightly packed chromatin, is composed of deactylated histones (due to histone deactylase activity) and is transcriptionally repressed. In contrast, euchromatin or relaxed chromatin is highly acetylated (due to histone acetylase activity) and transcriptionally active.
One function of catecholamines released by the adrenal glands during times of stress is to:
A) Stimulate secretion of melatonin by the pineal gland
B) Increase dilation of bronchioles in the lungs
C) Inhibit glucose reabsorption by the kidneys
D) Promote the release of digestive enzymes
B
During the stress response, catecholamines secreted from the adrenal medulla act to promote the “fight-or-flight” response. Some effects of catecholamines include redirected blood flow to maximize the delivery of oxygen and other nutrients to organs essential for immediate survival (brain, lungs, skeletal muscle), increased heart rate, and dilated airways.
The bones of humans and other vertebrates are alike in that they:
A) Consist solely of living tissue
B) Develop from the embryonic ectoderm
C) Form a rigid outer covering that protects the soft tissue inside the organism
D) Form an internal support structure that serves as a scaffold for soft tissues
D
The vertebrate endoskeleton is composed of both bone and cartilage and provides an internal scaffold that facilitates mobility while protecting and supporting internal organs. In contrast to vertebrates, many invertebrate animals possess an external skeleton (exoskeleton), which is a rigid outer covering that serves to protect the soft tissues underneath.
Which of the following experimental techniques can be used to detect the genetic material of a novel virus that injected its genome into a host Escherichia coli cell. Which was then translated into proteins and assembled within the cell itself.
A) Southern blot
B) DNA sequencing
C) Northern blot
D) Gene cloning
C
Northern blotting is a technique used to detect and measure the concentration of a specific RNA sequence in a cell or tissue sample. Southern blot is used to detect and measure the concentration of DNA in a cell. DNA sequencing is used to determine the specific nucleotide order of a DNA molecule, not viral RNA genomes. Gene cloning is used to generate many copies of a previously identified gene of interest, not good for detection of anything.
In an isolated population of mice, 10,000 mice are randomly sampled every 10 generations and their coat colors are recorded for a scientific study. The data for 100 generations of mice are shown in the graph below. (White coat mice decrease in number to almost 0, while black coat mice increase from almost 0 to 9,000)
Which of the following conclusions about the black and white mice in this population is best supported by the graph?
A) A population bottleneck caused the loss of white mice from the population but did not affect black mice
B) A mating event among white mice produced black mice that went on to have higher reproductive success than white mice
C) An environmental change resulted in natural selection for black mice but against white mice
D) A speciation event caused the lineage of white mice to split into a new species of black mice and decrease in frequency over time
C
In natural selection, beneficial traits that improve fitness are more likely to be passed to subsequent generations than less favorable traits. Beneficial traits should become more common with each generation, allowing the species to adapt to its environment.
To investigate how heteroplasmy influences disease manifestation, researchers analyzed an A to G substitution at nucleotide 3243 in the tRNA(leu) gene of mitochondrial DNA (mtDNA).
Which of the following would be true regarding the inheritance of the A3243G mutation, the known site of heteroplasmy discrepancies?
A) Assume daughters of an affected father are affected
B) Only offspring of affected mothers are affected
C) All affected males have asymptomatic carrier mothers
D) Affected offspring must have two copies of the defective gene
B
Mitochondria have their own genome, known as mitochondrial DNA, which is inherited in a maternal fashion (no paternal contribution). Mitochondria within sperm are not transferred into the ovum during fertilization; therefore, males never pass on their mitochondria.
Which of the following cell types would be LEAST sensitive to mitochondrial dysfunction due to mtDNA mutation?
A) Hepatocytes
B) Neurons
C) Myocytes
D) Erythrocytes
D
Erythrocytes are biconcave, disc-shaped cells containing hemoglobin, the carrier protein that delivers oxygen to body tissues. Erythrocytes contain no mitochondria as they expel their organelles during the maturation process in the bone marrow. As a result, mitochondrial mutations do not affect erythrocytes.
The image below shows a population of unicellular organisms. In each organism, the shaded mitochondria express a deleterious mutant allele of a mitochondrial gene, and the nonshaded mitochondria express wild-type allele of that same gene. (Diagram shows 4 cells becoming two, 2 of the 4 original have few deleterious alleles. The 2 in the second generation are highly deleterious).
Which of the following events most likely occurred between Generation 1 and Generation 2?
A) Meiosis
B) Population bottleneck
C) Natural selection
D) New mutation
B
Natural selection is the tendency for alleles that make an organism better suited for survival and reproduction to be passed along to the next generation. Bottleneck events reduce genetic diversity and change the allele frequencies of a population in a random way.
A standard PCR and PAGE gel electrophoresis was conducted to examine the blood samples of subjects with the 3243 region of the tRNA(leu) mutation. The PCR products were treated with the restriction enzyme Apal and visualized on the PAGE gel.
Based on this information, which of the following reagents was most likely used during PCR?
A) Free ribonucleoside triphosphate
B) RNA polymerase
C) A template sequence containing deoxyribonucleotides
D) Primer pairs with minimal GC content
C
Polymerase chain reaction (PCR) is a thermal cycling technique used to amplify DNA fragments. PCR reagents include a source DNA template, GC-rich primer pairs, a thermostable DNA polymerase, and a buffer solution with positively charged ions.
A physician determines that a patient has injured a connective tissue structure connecting two bones within the knee joint. Given this finding, the likely basis of the injury is damage to:
A) Skeletal muscle
B) Adipose tissue
C) A tendon
D) A ligament
D
Joints are structures of the musculoskeletal system where bones articulate (interact) and can range in mobility from freely moveable to immovable. Within moveable joints, strong connective tissue structures called tendons attach muscle to bone whereas ligaments attach bone to bone.
During a nutrition study, a participant consumes five times the physician-recommended amount of food but is unable to sufficiently absorb nutrients. Given this information, this participant would be LEAST likely to exhibit which of the following conditions?
A) Loss in diversity of bacteria that produce fatty acids in the large intestine
B) Decreased surface area in the small intestine
C) Heightened production of serum antibodies against intestinal proteins
D) Increased activity of nutrient transporter proteins in the small intestine
D
Nutrient absorption in the gastrointestinal tract is affected by the diversity of intestinal bacteria (gut flora), the surface area of the small intestine, and the functions of intestinal proteins (digestive enzymes, nutrient transporters, structural proteins). Intestinal nutrient transporters facilitate nutrient absorption from the intestinal tract into the body. Therefore, increased nutrient transporter activity would increase (not decrease) nutrient absorption.
Researchers are studying the last two phases of mitosis, anaphase and telophase, in actively dividing cancer cells. Different fluorescent probes are used to label various cellular components in these cells. Under the microscope, fluorescently labeled DNA appears blue, the nuclear envelope appears green, and the mitotic spindle appears red. Given this, green fluorescence would be most intense during:
A) Anaphase only
B) Telophase only
C) Both anaphase and telophase
D) Neither anaphase nor telophase
B
Mitosis in eukaryotic cells includes four distinct phases: prophase, metaphase, anaphase, and telophase. The nuclear envelope breaks down during prophase, allowing both metaphase and anaphase to occur in the cytoplasm. During telophase, the nuclear envelope reforms around the chromosomes prior to cytokinesis, the cytoplasmic division of the parental cell into two identical daughter cells.
A physician measures the arterial blood pressure of a patient while she is resting and again while she is running on a treadmill. The results of these blood pressure tests are given in the table below.
Resting 128/80
Running 155/73
Given this data, was arterial blood pressure during heart contraction higher while the patient was resting or while she was running?
A) Resting, because her diastolic blood pressure was higher when at rest
B) Resting, because her systolic blood pressure was higher when at rest
C) Running, because her systolic blood pressure was higher while running
D) Running, because her diastolic blood pressure was higher while running
C
Arterial blood pressure is highest when the heart contracts (during systole) and lowest when the heart relaxes (diastole). When measuring blood pressure (mm Hg), the higher systolic blood pressure is recorded over the lower diastolic blood pressure.
Which of the following DNA mutations would always lead to truncated PC1 if observed in the coding strand of the PKD1 gene shown below?
5’ …TGGTGCAACATTGCCTAG… 3’
A) Substitution of the second nucleotide for a thymine nucleotide
B) Deletion of the guanine nucleotide in the fifth position
C) Addition of three cytosine nucleotides after the third nucleotide
D) Insertion of an adenine nucleotide after the second nucleotide
D
Various types of DNA mutations can alter the protein product of a gene. Truncated proteins result from nonsense mutations and frameshift mutations with a downstream stop codon (UAA, UAG, UGA) in the new reading frame.
A woman whose father is heterozygous for an ADPKD-causing (Autosomal dominant polycystic kidney disease) mutation in PKD1 and whose mother is unaffected has a child with a man with no family history of ADPKD. What is the percent chance that their first child will have ADPKD? (Note: Assume the woman’s ADPKD status is unknown.)
A) 0%
B) 25%
C) 50%
D) 100%
B
In autosomal dominant inheritance, transmission of only one copy of a dominant allele is necessary to produce the phenotype. A heterozygous parent has a 50% chance of transmitting the mutation to their offspring.
P(child with ADPKD) = P(mother inherited 1 allele from her father) x P(mother passes this 1 allele to this child)
P(child with ADPKD) = (0.5)(0.5) = 0.25, or 25%
Approximately 85% of ADPKD cases are caused by mutations in the PKD1 gene, which codes for the protein polycystin-1 (PC1). The remaining 15% of cases are caused by mutations in the PKD2 gene, which codes for the protein polycystin-2 (PC2). The PC2 protein functions as a mechanically activated calcium (Ca2+) channel in ciliated renal epithelial cells.
Which set of amino acids would most likely be found in the pore of the channel formed by PC2? (Assume the amino acids are at a physiological pH.)
A) D and E
B) R and K
C) V and L
D) S and T
A
PC2 forms a mechanically activated Ca2+ channel. For positively charged Ca2+ to pass, the inside of the pore must be lined by amino acid residues that are negatively charged at physiological pH. Aspartate (D) and glutamate (E) are the only amino acids that fit this criterion. Arginine (R) and lysine (K) are both positively charged. The carbon-hydrogen side chains of valine (V) and leucine (L) are nonpolar and are unable to attract positively charged Ca2+. Serine (S) and threonine (T) are uncharged and polar. Although they could weakly attract Ca2+ via ion-dipole forces, aspartate (D) and glutamate (E) would bind Ca2+ more effectively.
Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people. The primary pathology is the development of numerous fluid-filled renal cysts that ultimately expand and severely impair kidney function.
In advanced ADPKD, all of the following components of physiological homeostasis would be disrupted EXCEPT:
A) Blood nitrogen levels
B) Blood pH
C) Leukocyte production
D) Erythropoietin production
C
The kidney’s primary function is to maintain the salt and water balance of the blood. They also play a key role in regulating multiple aspects of physiological homeostasis (blood pressure, waste removal, osmolarity, blood pH, erythrocyte production).
Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people. By age 60, approximately 50% of patients with ADPKD progress to end-stage renal disease (ESRD) and kidney failure.
Based on this information, is the mutated PKD1 allele, which codes for the protein polycystin-1 (PC1), likely to be eradicated from the gene pool by natural selection?
A) Yes, because the disease phenotype is masked by heterozygous genotypes
B) Yes, because inclusive fitness is improved for individuals under the age of 50
C) No, because the mutated allele is preserved by directional selection
D) No, because the disease phenotype does not emerge until after child-bearing age
D
Deleterious dominant alleles can remain in the gene pool if the organism’s fitness remains unaffected, even when the deleterious alleles reduce survival after the reproductive years. Deleterious recessive alleles evade elimination by natural selection through phenotypic masking in heterozygotes.
Eukaryotic organelles such as mitochondria and chloroplasts are believed to be relics of formerly free-living prokaryotes. The transition from hypoxic (low O2) to an oxic atmosphere (21% O2) is said to have enabled primitive eukaryotic anaerobes to engulf ancient aerobic prokaryotes and consequently acquire the ability to produce energy through oxidative phosphorylation. On integration into the host genome, mitchondria-derived genes became indistinguishable from the original nuclear genes.
Based on this information, which of the following best explains how mitochondrial genes differed from eukaryotic genes prior to gene transfer? Mitochondrial genes were:
A) Interspersed with noncoding sequences
B) Located on chromosomes without telomeres
C) Present on a single-stranded DNA genome
D) Associated with histones
B
In the nucleoid region of prokaryotic cells, double-stranded DNA is condensed into a circular chromosome that has no telomeres or associated histones. By contrast, eukaryotic cells package their histone-wrapped, double-stranded DNA into linear chromosomes with ends capped by telomeres to prevent DNA from unraveling.
Researchers have alternatively proposed that after a prolonged period of symbiosis, there is a possibility of gene transfer from eukaryotes to prokaryotes. This hypothesis was initially supported when copper/zinc (Cu/Zn) superoxide dismutase (SOD), a metalloprotein confined to the cytosol of eukaryotic cells, was found in Photobacterium leioghnathi.
Which observation would NOT support the hypothesis of gene transfer from eukaryotes to prokaryotes described in the passage?
A) Discovering no difference between the gene sequences of the P. leiognathi and pony fish SODs
B) Discovering P. leiognathi and ponyfish SODs have a similar amino acid sequence in their noncatalytic domains
C) Discovering Cu/Zn SODs in other free-living bacterial species with no known eukaryotic symbiotic hosts
D) Discovering Cu/Zn SODs in other free-living bacterial species with known eukaryotic symbiotic hosts
C
The endosymbiotic theory explains how primitive eukaryotic anaerobes engulfed ancient aerobic prokaryotes, and consequently acquired the ability to produce energy through oxidative phosphorylation. The discovery of Cu/Zn in free-living bacteria with no known eukaryotic symbiont hosts would argue against the hypothesis.
A hypothesis was initially supported when copper/zinc (Cu/Zn) superoxide dismutase (SOD), a metalloprotein confined to the cytosol of eukaryotic cells, was found in Photobacterium leiognathi, a free-living bacterium.
SOD mRNA in P. leiognathi encodes a signal sequence that directw the transport of the SOD protein for secretion. This signal sequence will direct SOD proteins to which strucure in P. leiognathi?
A) Smooth endoplasmic reticulum
B) Plasma membrane
C) Mitchondrial outer membrane
D) Golgi body
B
Prokaryotic cells lack membrane-bound organelles and utilize specialized channels in the plasma membrane to secrete proteins. In contrast, eukaryotic cells contain membrane-bound organelles (nucleus, Golgi body, mitochondria); the rough endoplasmic reticulum and Golgi body are involved in eukaryotic protein secretion.
Ponyfish cells containing P. leiognathi (a free-living bacterium) symbionts were exposed to a spindle fiber toxin that inhibits microtubule polymerization. Given this information, which of the following would most likely results as a consequence of toxin exposure?
A) P. leiognathi daughter cells with multiple copies of the Cu/Zn SOD gene
B) Ponyfish daughter cells containing the same number copy number of the Cu/Zn SOD gene
C) Delayed separation of P. leiognathi cells during binary fission
D) Nondisjunction in somatic ponyfish cells undergoing nuclear division
D
Most eukaryotic cells (except germ cells) undergo cell division via mitosis. In contrast, prokaryotic cells duplicate via binary fission, a simple form of reproduction that does not involve the separation of chromosomes by spindle fibers. Nondisjunction in mitosis or meiosis can occur when sister chromatids fail to separate properly during anaphase. Ponyfish cells exposed to a spindle fiber toxin would exhibit nondisjunction during mitosis as spindle fibers are necessary to separate sister chromatids.
Investigators used a ribosome profiling technique to measure the level of SOD protein synthesis in P. leiognathi and ponyfish cells during radioactive oxygen species (ROS) accumulation. P. leiognathi cells were found to contain greater numbers of ribosome/SOD mRNA complexes than ponyfish cells. What is the best explanation for this result?
A) P. leiognathi SOD mRNA is capable of being bound by more than one ribosome
B) P. leiognathi SOD mRNA has a greater affinity for ribosomes than ponyfish mRNA
C) mRNA transcribed from the ponyfish SOD gene undergoes immediate degradation
D) mRNA transcribed from the bacterial SOD gene is being transcribed simultaneously
D
Prokaryotic cells have no nucleus; therefore, transcription and translation occur simultaneously in the cytoplasm (translation begins before the mRNA is fully transcribed). By contrast, in eukaryotic cells transcription and post-transcriptional modifications occur in the nucleus, but translation occurs in the cytoplasm.
In anaerobic environments, P. leiognathi can produce energy by using an inorganic final electron acceptor other than oxygen in the electron transport chain. Under anaerobic conditions, which of the following is NOT active in ponyfish cells but active in P. leiognathi?
A) Glycolysis
B) Gluconeogenesis
C) Fermentation
D) ATP synthase
D
The Krebs cycle and the electron transport chain are only active in the presence of a final electron acceptor, such as oxygen (aerobic respiration) or inorganic ions (anaerobic respiration). Although ATP synthase does not directly need O2 to generate ATP, the formation of the proton gradient by which it functions is oxygen-dependent in ponyfish cells but not in P. leiognathi. Consequently, under anaerobic conditions, ATP synthase is not active in ponyfish cells but active in P. leiognathi.
A neuron is exposed to a compound that prevents the passage of Na+ channels. Which of the following graphs best represents the local membrane potential charge of this neuron upon injection of positive current that allows the membrane to reach the threshold value? (Note: The solid line represents the action potential after normal stimulation; the dashed line represents the action potential after exposure to the compound.)
Answers are graphs*
A) No relative change
B) Once reaching threshold, does not continue depolarization. Back to resting potential
C) Resting membrane potential is higher than normal, depolarization normal
D) Once depolarization occurs, graphs tapers off at high resting membrane potential. Does not go back to under threshold levels
B
An action potential is fired in an all-or-nothing manner based on the cell’s membrane potential. If the threshold is reached, voltage-gated ion channels open and the membrane rapidly depolarizes. The resting membrane potential is restored by the Na+/K+ pump.
Biologist 1 developed a neural staining technique that involved older animal’s myelinated axons. Biologist 2 modified the first biologist’s study by using the brain tissue of younger animals, rather than older more myelinated brain tissue samples.
Compared to the axons investigated by Biologist 2, the axons studied by Biologist 1 most likely had:
A) Faster decay of the propagating electrical signal
B) Axonal membranes that were more exposed to the extracellular space
C) Slower rates of action potential conduction
D) Voltage-gated ion channels clustered only at specific locations
D
The myelin sheath increases the speed of action potential (AP) propagation by acting as an electrical insulator that prevents dissipation of charge across the membrane. APs in myelinated axons travel via saltatory conduction. Due to the lack of myelination, the axons studied by Biologist 2 were fully exposed to extracellular space, were more susceptible to rapid weakening of the electrical signal, and conducted APs at a slower rate.
Which of the following synaptic events is most likely to contribute to the generation of an action potential in a postsynaptic neuron?
A) The presynaptic neuron releases large quantities of gamma-aminobutyric acid (GABA)
B) Postsynaptic neurotransmitter-gated ion channels that pass both Na+ and Ca2+ ions open
C) Neurotransmitter reuptake into the presynaptic cell and surrounding glia is inhibited
D) Neurotransmitter binding activates G-protein coupled receptors on the postsynaptic membrane
B
Although trends in neurotransmitter function exist, the postsynaptic response is ultimately determined by the type of receptor activated. Receptors may be either ligand-gated ion channels or G-protein-coupled receptors. In chemical synapses, when an action potential (AP) reaches the axon terminal of the presynaptic neuron, the terminal membrane depolarizes and causes voltage-gated Ca2+ channels to open. Extracellular Ca2+ ions flow down their electrochemical gradient into the axon terminal and stimulate neurotransmitter-containing synaptic vesicles to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis.
A single diploid cell containing 46 chromosomes underwent meiosis and produced four daughter cells, two with 22 chromosomes and two with 24 chromosomes. An error in which of the following stages of meiosis would most likely explain this result?
A) Metaphase II
B) Prophase II
C) Telophase I
D) Anaphase I
D
During meiosis, chromosomal nondisjunction occurs when homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II) fail to separate to opposite poles of the cell during anaphase, leading to extra chromosomes in some daughter cells and missing chromosomes in others.
A gene regulating tail length in bobtail cats has a genetic variation at a single locus, where organisms can have an allele that produces long tails (L) or an allele that produces long short tails (l). A male cat homozygous for short tail length (ll) was mated with a female cat homozygous for long tail length (LL). The tail lengths of the parents and offspring were recorded.
Father is short, mother is long
All offspring are a variation between mom and dad tail length. (None are longer or short than the parents)
A scientist concludes that the alleles regulating tail length in these cats exhibit incomplete dominance. Do the data support this conclusion?
A) No, because all offspring have longer tails than the father’s
B) No, because all offspring inherited both types of alleles for tail length
C) Yes, because the tail lengths of some offspring are longer than the tail lengths of other offspring
D) Yes, because the offspring have tail lengths longer than the father’s but short than the mother’s
D
Incomplete dominance between alleles results in the expression of phenotypes in heterozygous offspring that are intermediate to the phenotypes of homozygous parents. Long tail mother mixed with short tail father will results in medium tail in the offspring when dealing with incomplete dominance.
Renal studies in mice have revealed that a mutation in various sodium transporters causes impaired active transport of NaCl from the filtrate within the Loop of Henle to the medulla. If mice with wild-type sodium transporters were compared to mice with the mutated sodium transporters, the mutant mice would likely exhibit all of the following EXCEPT:
A) Decreased saltiness of the medulla
B) Decreased urine output
C) Decreased renal water reabsorption
D) Decreased blood pressure
B
In the loop of Henle, active transport of NaCl from filtrate in the ascending limb maintains the saltiness of the renal medulla, facilitating passive water reabsorption from filtrate on the descending limb and collecting duct. Compared to wild-type mice, mice with mutated sodium transporters would exhibit a decrease in both medullary salt concentration and water reabsorption, a decrease in blood pressure, and an increase in urine output.
Certain turtle species exhibit embryonic expression of an enzyme that converts male sex hormones to female sex hormones. The enzyme expression level determines whether a developing embryo will be male or female. Scientists hypothesize that expression of this enzyme depends on incubation temperature during development. To test this, they incubated 30 turtle eggs at 26C and 30 eggs at 30C and recorded the sex of each turtle after hatching.
Graph depicts high amount of male turtles and low female at 26C and high amount of female turtles, low males at 30C
Given this, the expression level of this enzyme in developing turtles is most likely:
A) High at 26C and low at 30C
B) Low at 26C and high at 30C
C) High at both 26C and 30C
D) Low at both 26C and 30C
B
In general, the expression of genes produces proteins, and the properties and activities of these proteins lead to the expression of certain traits (phenotypes) in organisms. However, in a gene-environment interaction, certain environmental conditions (temperature, diet, oxygen level) can influence gene expression or protein activity and alter an organism’s phenotype.
Skin grafts are used for partial-thickness burns, which damage the epidermis and dermis, and for full-thickness burns, which damage the epidermis, dermis, and hypodermis. Superficial burns injure only epidermal tissue and heal without skin grafts.
A skin graft candidate with full-thickness burns on approximately 50% of the total BSA is at risk for all of the following EXCEPT:
A) Extensive fluid loss
B) Bacterial infection
C) Increased sensitivity to touch
D) Vitamin D deficiency
C
The skin functions as a physical barrier to prevent the loss of fluid from the body while simultaneously blocking the entry of pathogens or harmful chemicals. The skin also contains receptors that gather and respond to sensory information from the surrounding environment. Ultraviolet radiation that strikes the skin induces the synthesis of a vitamin D precursor. This type of burn involves injury to the epidermal and dermal sensory receptors, resulting in impaired touch sensation.
Heat acclimation (HA) is the process by which the body increases heat tolerance through adaptive changes in the sympathetic control of skin heat dissipation. It can be induced in healthy individuals by repeated exercise at elevated ambient temperature and humidity.
A group of researchers tested whether skin graft recipients could also undergo HA. What physiological change occurs in the skin of control (healthy) subjects during HA exercise?
A) Enhanced contraction of arteriole smooth muscle
B) Enhanced relaxation of arteriole smooth muscle
C) Enhanced contraction of arrector pili muscles due to parasympathetic activation
D) Enhanced contraction of arrector pili muscles due to sympathetic activation
B
One major function of the skin is thermoregulation. Body temperature can be increased by vasoconstriction of skin arterioles, shivering, and (in hairer animals) piloerection, hair standing upright. Body temperature can be decreased by vasodilation of skin arterioles and sweating.
Given that scar tissue forms when collagen-producing cells replace normal tissue after an injury, all of the following processes would be impaired in the area of scarred skin that forms over a partial-thickness burn EXCEPT:
A) Resistance to ultraviolet radiation
B) Insulation
C) Hair growth
D) Salt excretion
B
Skin has many functions: The subcutaneous layer is composed of adipose cells that insulate the body, epidermal melanocytes prevent UV radiation from damaging the DNA of cells, hair is a keratinized derivative of skin that helps protect the body from external injury, and dermal sweat glands secrete swear onto the skin surface to regulate body temperature. Based on the question, a partial-thickness burn does not affect the subcutaneous layer, so insulation is not affected.
Which of the following skin functions will most likely be impaired in tissue with superficial burns?
I. Keratinocyte maturation
II. Immune surveillance
III. Shock absorption
A) I and II only
B) I and III only
C) II and III only
D) I, II, and III
A
The skin is divided into the epidermis (outermost layer), dermis (middle layer), and hypodermis (innermost layer). The epidermis acts a physical barrier that separates the organism from the external environment. The dermis contains blood vessels, immune cells, sensory receptors, sweat and oil glands, and hair follicles. The hypodermis is composed of insulating and shock-absorbing adipose tissue. Since the burn is only superficial, shock absorption will not be affected.
Bacteria are removed from lymph and blood in the:
A) Spleen and bone marrow, respectively
B) Lymph nodes and spleen, respectively
C) Bone marrow and lymph nodes, respectively
D) Lymph vessels and thymus, respectively
B
In the lymph nodes, white blood cells remove and mount immune responses against pathogens from the lymph, whereas in the spleen, white blood cells remove pathogens and damaged or old red blood cells from the blood.
A physician finds that a patient experiences excessive bleeding after sustaining a cut on the arm. The excessive bleeding is LEAST likely to be caused by:
A) Reduced liver function
B) High numbers of macrophages near the cut
C) Reduced proliferation of platelets
D) High levels of serum antibodies against clotting factors
B
Platelets and specialized proteins (clotting factors) work synergistically in response to blood vessel damage, binding to the damaged portion of the vessel and forming a blockage that prevents blood loss. Although macrophages may destroy pathogens entering the body through the cut, they would not inhibit clot formation and cause excessive bleeding that was observed in the patient.
A patient found to have an abnormally low number of helper T cells in her blood contracts a bacterial infection. During the infection, which of the following is most likely NOT affected by the patient’s low count of helper T cells?
A) Expression of major histocompatibility complex proteins that present bacterial antigens on the membrane of infected host cells
B) Proliferation of B lymphocytes in response to the bacterial infection
C) Levels of circulating antibodies against the invading bacterium
D) Activation of apoptosis-inducing cytotoxic T cells
A
Helper T cells bind foreign antigens presented by other immune cells and release signaling molecules than enhance immune responses, such as cytotoxic T cell activation and antibody production by lymphocytes. Some of the lymphocytes also secrete antibodies and increase levels in circulation.
Which of the following mRNA strands contains the longest open reading frame?
A) 5’ - CCACGAUGCGUUGAGCGC - 3’
B) 5’ - CAAUGGUAAAGUCUUAGU - 3’
C) 5’ - GACGAUGUAACUUGCACU - 3’
D) 5’ - AGAAUGGUAUCCUGAGCC - 3’
B
An open reading frame (ORF) is a set of codons within a strand of mRNA that can be translated by a ribosome. An ORF begins with a start codon (AUG) and ends with a atop codon (UAA, UAG, or UGA). The start and stop codons must be in the same reading frame.
Type 1 diabetes mellitus (T1DM) differs from T2DM in that affected patients stop producing insulin at a young age. Which of the following is most likely impaired in T1DM?
I. Exocrine function of pancreatic beta cells
II. Endocrine function of pancreatic beta cells
III. Exocrine function of pancreatic alpha cells
IV. Endocrine function of pancreatic alpha cells
A) I only
B) II only
C) I and II only
D) III and IV only
B
In the setting of high blood glucose, beta cells release insulin to promote glucose uptake from the blood and inhibit alpha cell function. In contrast, when blood sugar levels are low, alpha cells produce glucagon to promote glucose release into the bloodstream and inhibit beta cell function. Cells with endocrine (pancreas) function secrete hormones into the bloodstream to cause an effect in a different part of the body.
Intraperitoneal injection of insulin would cause the peptide hormone to enter the bloodstream and exert its effect on target cells by:
A) Acting as a second messenger
B) Diffusing through the plasma membrane
C) Binding an extracellular from a carrier protein
D) Disassociating from a carrier protein
C
Peptide hormones are amino-acid based, water-soluble molecules that travel freely through the bloodstream and act as first messengers by binding to an extracellular receptor on the target cell membrane, which leads to activation of intracellular second messengers.
During the interval between 30 and 60 minutes in the graph, which of the following will be observed in WT mice?
(Graph shows a decrease of glucose levels as time progresses from 30 minutes to 60 minutes after injection of glucose)
A) Increased glucagon release
B) Increased plasma amino acids
C) Increased hepatic glycogen stores
D) Increased hepatic gluconeogenesis
C
In the setting of high blood glucose, insulin is released in response and functions to decrease blood glucose levels. In contrast, glucagon is released from pancreatic alpha cells in response to increase glucose levels. Insulin decreases blood glucose in the 30-60 minute interval by promoting glucose uptake by the liver for glycogen synthesis, which increases hepatic glycogen stores.
Recently fed leptin-deficient mice (obese) show deficient binding of glucagon to its G protein-coupled receptor, which most likely leads to:
A) Decreased cAMP to ATP conversion
B) Upregulated adenylate cyclase activity
C) Increased exchange of GDP to GTP
D) Reduced protein kinase A activity
D
In the G protein-regulated cAMP signaling pathway, a ligand binds the transmembrane G protein-coupled receptor and activates the GDP-bound alpha subunit of the G protein by replacing GDP with GTP. The activated G alpha subunit activates the enzyme adenylyl cyclase, which catalyzes the conversion of ATP into cAMP. Elevated cAMP leads to the activation of protein kinase A and subsequent signaling effects. Deficient binding of glucagon to its G protein-coupled receptor would decrease adenylate cyclase activity, which would result in reduced conversion of ATP to cAMP, not cAMP to ATP.
Researchers aimed to cause obesity-induced insulin resistance in wild-type (WT) mice and Alb Tg mice, which express hepatic miR-26a (has been implicated in prevention of obesity-induced insulin resistance) at levels three-fold greater than WT. WT mice and Alb Tg mice were fed either a standard healthy diet (SHD) or a high-fat diet (HFD) for 14 weeks.
The researchers hypothesize that miR-26a overexpression can rescue obesity-induced insulin resistance. Which experimental result would NOT support their hypothesis?
A) Alb Tg mice fed a HFD had the same levels of random and fasting insulin as WT mice fed a SHD
B) Alb Tg mice fed a HFD had the same levels of random and fasting glucose as WT mice fed a SHD
C) WT mice fed a HFD had higher insulin sensitivity than Alb Tg mice fed a HFD
D) WT mice fed a HFD had lower glucose tolerance than Alb Tg mice fed a HFD
C
An organism is considered insulin sensitive if only a minimal amount of insulin is needed to induce an appropriate reduction in glucose levels. In contrast, insulin-resistant organisms need substantially more insulin to take up the same amount of glucose.
One of the study subjects with a BMI of 56 kg/m^2 is discovered to have a similar pathology to the ob/ob mouse. Like ob/ob mice, affected individuals exhibit normal weight at birth but become severely obese afterward and have undetectable levels of leptin in the serum. What is the best explanation of serum leptin in this condition?
A) Leptin cannot bind its receptor in the hypothalamus
B) Leptin cannot bind its receptor in the thyroid gland
C) Leptin cannot be secreted from gastric cells
D) Leptin cannot be secreted from adipocytes
D
In an energy-rich state (after a meal), leptin is released by white adipocytes to trigger appetite suppression via the hypothalamus. In contrast, in an energy-poor state, ghrelin is released by stomach gastric cells to trigger hunger and food-seeking behavior via the hypothalamus.
COPD refers to a spectrum of disorders and can be a result of emphysema, the irreversible destruction of pulmonary tissue. The breakdown of elastic proteins in the lungs results in a loss of pulmonary resiliency and chronic lung hyperventilation.
According to this information, which of the following changes would be expected in a patient with signs of emphysema?
A) Narrowing of the trachea
B) Less efficient gas exchange
C) Weakened diaphragm muscle
D) Overstretched pharyngeal tissues
B
The alveoli are highly efficient at gas exchange due to their structure and extensive surface area. The destruction of alveolar walls in emphysematous lungs is expected to decrease the lungs’ ability to perform respiratory gas exchange.
Lung diseases can be diagnosed and monitored using spirometry. A spirometer measures the flow rate and volume of inhaled and exhaled air. In one pulmonary test, a patient is asked to exhale forcibly and completely into a spirometer after maximum inhalation. This is to test forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), the total amount of air exhaled in a single breath.
If presented with a graph, which would be expected to pair with a patient with asmtha?
A) FEV1 lower than normal patient, without reaching same maximum breath exhaled
B) FEV1 lower than normal patient, but reaches same maximum breath exhaled
C) FEV1 reaches height slightly faster than normal patient, and roughly same maximum breath exhaled
D) FEV1 reaches height much faster than normal patient, has exact same maximum breath exhaled
A
The narrowing of respiratory airways in asthma increases resistance to airflow, which would decrease the volumetric rate of forcibly exhaled air (FEV1 decreases). The narrow airways also trap air in the lungs, decreasing the total volume of air that can be exhaled (FVC decreases). Less air can be exhaled in asthma due to air trapping in the lungs.
The regulation of respiratory rate is normally most sensitive to: Partial pressure = P A) P O2 in the blood B) P CO2 in the blood C) P O2 in the alveoli D) P CO2 in the alveoli
B
The regulation of respiratory rate primarily depends on the pH of the blood as measured by central and peripheral chemoreceptors. These receptors directly detect the [H+] in the blood, which is dependent on the partial pressure of CO2 in the blood through the bicarbonate buffer system. (CO2 + H2O H2CO3 HCO3- + H+)
During an asthma attack, temporary bronchoconstriction would have what effect on blood pH, and what would be the expected homeostatic response?
A) Respiratory acidosis and an increased respiratory rate
B) Respiratory acidosis and a decreased respiratory rate
C) Respiratory alkalosis and an increased respiratory rate
D) Respiratory alkalosis and a decreased respiratory rate
A
Respiratory gas exchange functions to remove CO2 from the blood, and CO2 levels affect the pH of the blood by shifting the equilibrium of the bicarbonate buffer system. A decrease in gas exchange will cause respiratory acidosis, and the body will attempt to restore normal blood pH by increasing the respiratory rate.
(CO2 + H2O H2CO3 HCO3- + H+)
The inflation of the lungs in normal inspiration involves:
I. Contraction of the diaphragm
II. Reduction of intrapleural pressure
III. Elevation of the rib cage
A) I and II only
B) I and III only
C) II and III only
D) I, II, and III
D
The intrapleural space is the thin space between the lungs and the thoracic wall. The contraction of the diaphragm and the elevation of the rib cage decreases the pressure in the intrapleural space, causing the lungs to expand. Negative pressure breathing refers to the reduction of intrapleural pressure during inspiration.
Primary ciliary dyskinesia (PCD), a rare disease that impairs the normal function of cilia, is often misdiagnosed as atypical asthma because wheezing is observed in both illnesses. Unlike asthma, PCD would cause the inability to:
A) Balance respiratory thermoregulation
B) Cough or sneeze
C) Remove inhaled particulates
D) Speak in lower pitches
C
In the upper respiratory tract, mucus-producing cells and ciliated cells work together to trap and remove potentially pathogenic bodies. Therefore, dysfunctional cilia would decrease the respiratory system’s ability to remove inhaled particulates.
If using antibodies to test for Rheumatoid arthritis (RA) what would they most likely contain?
A) Two heavy chains that differ in amino acid sequence
B) Two light chains that differ in amino acid sequence
C) A variable region that binds only one type of antigen
D) A constant region that binds only one type of antigen
C
Antibodies are synthesized and secreted by effector B cells, which are part of the adaptive immune system. Each antibody consists of two identical light chains, two identical heavy chains, a variable region that interacts with a specific antigen, and a constant region that interacts with the cells (phagocytes) and proteins of the body to facilitate antigen destruction.
