Missed B/B questions Flashcards
What is the total number of fused rings in a Steroid?
4
Epilepsy may result in motor seizures due to massive synchronous firing of neurons in a small area of the cerebral cortex (the epileptic focus). Excitation spreads from the focus, involving an increasingly larger area of the cortex. A drug for the treatment of epilepsy would be most effective if it caused which of the following changes in the epileptic focus?
A.
An increase in the neuron-firing threshold
B.
An increase in extracellular Na+ concentration
C.
A decrease in axon–membrane permeability to negative ions
D.
A decrease in the length of the depolarization stage
A
A drug that would best treat epilepsy, as described, should reduce the activity of the neurons in the epileptic focus, which are excitatory neurons based on their effect throughout the cortex. The answer to this question is A because increasing the threshold required to generate an action potential would decrease the chance that individual neurons would fire, thus reducing the overall amount of excitation that spreads from the epileptic focus throughout the cortex.
When concentrated urine is being produced, in which of the following regions of the kidney will the glomerular filtrate reach its highest concentration?
A.
Proximal convoluted tubule
B.
Distal convoluted tubule
C.
Cortical portion of the collecting duct
D.
Medullary portion of the collecting duct
The answer is D because glomerular filtrate is most concentrated in the medullary portion of the collecting duct, compared to the other kidney structures listed.
What is the function of transcription factors?
They may bind directly to special “promoter” regions of DNA, which lie upstream of the coding region in a gene, or directly to the RNA polymerase molecule. They recruit RNA polymerase
What do ABC transporters do?
ABC transporters utilize the energy of ATP binding and hydrolysis to transport various substrates across cellular membranes.
What is a lipid raft?
Lipid rafts are defined as cholesterol- and sphingolipid-enriched membrane domains and numerous studies have attempted the lipid characterization of caveolae and raft domains.
What is an oligosaccharide?
a carbohydrate whose molecules are composed of a relatively small number of monosaccharide units.
The initial filtration step in the glomerulus of the mammalian kidney occurs primarily by:
A.
passive flow due to a pressure difference.
B.
passive flow resulting from a countercurrent exchange system.
C.
active transport of water, followed by movement of electrolytes along a resulting concentration gradient.
D.
active transport of electrolytes, followed by passive flow of water along the resulting osmolarity gradient.
The answer to this question is A because the initial filtration in the glomerulus occurs as blood pressure forces the fluid from the glomerulus into the lumen of Bowman’s capsule.
Enzymes alter the rate of chemical reactions by all of the following methods EXCEPT:
A.
co-localizing substrates.
B.
altering local pH.
C.
altering substrate shape.
D.
altering substrate primary structure.
The answer to this question is D. The primary structure of a protein substrate is the amino acid sequence of the protein. Enzymes cannot alter primary structures of protein, but can colocalize substrates, alter local pH, and alter substrate shape.
The statement that the ornithine decarboxylase assay is highly specific means that it:
A.
requires radioactive ornithine of high specific activity.
B.
generates diaminobutane of high specific activity.
C.
an distinguish ornithine decarboxylase activity from the many other enzymatic reactions in a cell.
D.
can measure the small amount of ornithine present in a cell.
The answer to this question is C because enzymes such as ornithine decarboxylase are highly specific both in the reactions that they catalyze and in their choice of substrates and therefore catalyze only a single chemical reaction or occasionally a set of closely related reactions.
The lung cells of heavy smokers would be expected to have greatly increased concentrations of cP-450 and:
A.
DNA sequences that code for cP-450.
B.
mRNA sequences that code for cP-450.
C.
rRNA that process cP-450.
D.
tRNA that are specific for cysteine.
The answer to this question is B, because protein levels relate most directly to mRNA levels.
The role of cP-450 in the metabolism of toxins may be exemplified by the following case in which a chronic alcoholic died of a barbiturate overdose.
While sober, the alcoholic was having trouble falling asleep and, therefore, took the recommended dosage of sleeping pills (barbiturates). When no drowsiness was felt, the alcoholic consumed more sleeping pills, then drank an alcoholic beverage. Severe respiratory depression and death soon followed caused by an overdose of barbiturates. An autopsy revealed that if alcohol had not been present, the barbiturates would have been metabolized rapidly enough to be eliminated by the body, and death would not have occurred.
No drowsiness was initially felt by the alcoholic because the previous abuse of alcohol had:
A.
denatured the cP-450.
B.
inhibited the cP-450.
C.
reduced the cP-450.
D.
induced the cP-450.
The answer to this question is D, because the passage states that cP-450 is inducible and thus previous abuse of alcohol, a cellular toxin, results in an increased concentration of cP-450. This leads to rapid barbiturate metabolism by cP-450 and the absence of initial drowsiness.
What happens during interphase?
Interphase is the phase of the cell cycle between cell divisions and is the phase in which the cell obtains nutrients, grows, reads its DNA, and conducts other “normal” cell functions.
Do mammilian erythrocytes contain DNA?
No. Erythrocytes lose their nuclei during maturation
Which of the following best describes the bond that would form between the following two nucleotides if they were located adjacent to each other as shown in a single strand of DNA?
A.
A bond between the phosphate of the thymine and the phosphate of the adenine
B.
A bond between an oxygen in the thymine base and a nitrogen in the adenine base
C.
A bond between the phosphate of the thymine and the sugar of the adenine
D.
A bond between the phosphate of the adenine and the sugar of the thymine
The answer to this question is D because nucleotides are linked to one another by phosphodiester bonds between the sugar base of one nucleotide and the phosphate group of the adjacent nucleotide in a way that the 5’ end bears a phosphate, and the 3’ end a hydroxyl group.
ACTH function
Adrenocorticotropic hormone (ACTH) is made in the pituitary gland. … ACTH stimulates the release of another hormone called cortisol from the cortex (outer part) of the adrenal gland. … Secretion of ACTHis controlled by three regions of the body, the hypothalamus, the pituitary gland ..
the uptake of glucose. However, insulin does stimulate the first step in the glycolytic pathway within the liver. Therefore, in liver cells, insulin most likely:
A.
hinders glucose uptake by increasing the cellular concentration of glucose.
B.
aids glucose uptake by decreasing the cellular concentration of glucose.
C.
hinders glucose uptake by using the ATP needed by the glucose transporter proteins.
D.
aids glucose uptake by providing the ATP needed by the glucose transporter proteins.
The answer to this question is B because the stem states that insulin stimulates the first step in the glycolytic pathway in the liver, thus decreasing the cellular concentration of glucose. This results in increased uptake of glucose to maintain the cellular concentration of glucose.
During the production of insulin, the translated polypeptide is cleaved into the mature form and secreted from the cell. The cleavage most likely takes place in which of the following locations?
A.
Nucleus
B.
Ribosomes
C.
Endomembrane system
D.
Cytoplasm
The answer to this question is C because secreted proteins such as insulin are cleaved into mature form within endomembrane system.
A certain bacterium was cultured for several generations in medium containing 15N, transferred to medium containing 14N, and allowed to complete two rounds of cell division. Given that the bacterium’s genome mass is 5.4 fg when grown in 14N media and 5.5 fg when grown in 15N medium, individual bacteria with which of the following genome masses would most likely be isolated from this culture?
A.
5.4 fg only
B.
5.4 fg and 5.45 fg
C.
5.4 fg and 5.5 fg
D.
5.45 fg only
The answer to this question is B because DNA replication is semi-conservative. Therefore, after the first round of cell division the genome mass in each bacterium will be 5.45 fg (one DNA strand will contain 15N and the other strand 14N). Following the second round of cell division, half of the bacteria will have a genome mass of 5.4 fg (14N exclusively) and the other half a mass genome of 5.45 fg (14N in one DNA strand and 15N in the other).
A stable, differentiated cell that will NOT divide again during its lifetime would most likely be found in which of the following stages of the cell cycle?
A. G1
B. G2
C. M
D. S
The correct answer is A.
The question asks the examinee to identify the cell cycle stage in which a stable, differentiated, nondividing cell will most likely be found. A diploid, nondividing cell is most likely in G0 or G1, in which the cell remains metabolically active but is not replicating its DNA (S) or segregating its duplicated chromosomes and dividing (M). A is the only option that lists either G0 or G1. Thus, A is the best answer.
Most viral proteins are produced directly by:
A. translation of host nucleic acid.
B. translation of viral nucleic acid.
C. transcription of host nucleic acid.
D. transcription of viral nucleic acid.
The correct answer is B.
Transcription is copying; translation is changing the language. In cellular metabolism transcription refers to taking DNA and making an RNA copy; translation refers to taking the RNA, a series of nucleotides, and putting it into protein language, a series of amino acids. Some viruses have a genome consisting of RNA and this can be directly translated by the ribosome. Others use DNA as the genetic material and require transcription as well. Both, however, ultimately make proteins by translating their specific RNAs into protein, so the answer is B.
If the DNA of a representative species from each of the major kingdoms was examined, the sequences coding for which of following would be expected to be most similar?
A. Photosynthesis
B. Cholesterol synthesis
C. Protein modification
D. DNA synthesis
D is correct. DNA sequences that are common among different species, phyla, or even kingdoms are called conserved sequences. Conserved sequences tend to remain that way due to the fact that they code for a vital function that is common among disparate species.
Which of the following is an accurate statement regarding mitosis and meiosis?
A. Mitosis results in two haploid daughter cells.
B. During mitosis and meiosis II, sister chromatids are separated.
C. During meiosis I and meiosis II, sister chromatids are separated.
D. Meiosis I results in two diploid daughter cells.
B is correct. This question is asking us to recall some facts about mitosis and meiosis. Remember that mitosis separates sister chromatids to create two diploid daughter cells. Meiosis I separates homologous chromosomes to create haploid daughter cells, each of which divides again, separating sister chromatids in Meiosis II to create two haploid cells.
Do bacteria contain introns?
For the most part, bacteria lack introns, whereas large eukaryotic genes usually contain several introns. A large, eukaryotic gene without introns suggests a bacterial origin.
Which of the following changes occur immediately following the consumption of a carbohydrate-rich meal?
A. Insulin secretion decreases; G6PD activity increases.
B. Insulin secretion decreases; G6PD activity decreases.
C. Insulin secretion increases; G6PD activity increases.
D. Insulin secretion increases; G6PD activity decreases.
C is correct. From outside knowledge, we know that insulin secretion increases after a meal to help the cells take up glucose from the bloodstream. The passage states that the PPP is a parallel (alternative) path to glycolysis, so it makes sense that it would also be activated when blood sugar levels rise after a meal.
In severe diabetic hyperglycemia (high blood sugar), insulin cannot effectively induce the uptake of glucose by cells. Chronic hyperglycemia directly leads to the presence of which of these molecules in the urine?
I. Proteins
II. Glucose
III. Ketone bodies
Glucose and Ketone Bodies
C is correct. This question requires outside knowledge about glucose metabolism. If cells cannot take up glucose, it will remain in the blood and eventually be excreted in the urine when it builds up to the point that it cannot be reabsorbed by the nephron. In a state of extended hyperglycemia, the body relies on fat metabolism to generate energy, which produces ketone bodies that are also excreted in the urine. Therefore, Roman numerals II and III are correct.
Meiosis I results in:
A. 2 diploid cells with 46 chromosomes, each chromosome consisting of 2 sister chromatids.
B. 2 haploid cells with 46 chromosomes, each chromosome consisting of 1 chromatid.
C. 2 haploid cells with 23 chromosomes, each chromosome consisting of 2 sister chromatids.
D. 2 diploid cells with 23 chromosomes, each chromosome consisting of 1 chromatid.
C is correct. Meiosis I results in 2 haploid cells, each with 23 chromosomes consisting of 2 sister chromatids per chromosome. In the male, the sister chromatids are split into 4 gametes during meiosis II. For females, meiosis I results in a secondary oocyte (a gamete) and a polar body. Penetration of the secondary oocyte by a sperm brings on anaphase II. Telophase II produces a zygote and a second polar body. Remember for the MCAT: mitosis results in diploid daughter cells, while meiosis results in haploid cells to produce gametes.
The concentration of intracellular signaling molecules fluctuates rapidly in dividing cells during the cell cycle. Which of the following experimental techniques would be best to elucidate the mechanism of regulation for these proteins?
A. RT-PCR and Southern blot
B. Southern blot and northern blot
C. Western blot and RT-PCR
D. Western blot and Southern blot
C is correct. Rapidly dividing cells undergo mitosis under the influence of specific signaling molecules. These molecules are expressed when their genes are transcribed, then are translated into proteins. In order to gain the best understanding of how a signaling protein’s levels are regulated, both the protein and mRNA levels would need to be studied. Western blotting gives us information about the amount of protein expressed in a cell, while RT-PCR gives us information about the amount of RNA expressed
What is a nucleoside?
A nucleoside is composed of a nitrogenous base and a five-carbon sugar (ribose or deoxyribose). Adenosine, shown below, is such a molecule
Folate is a common supplement given to pregnant women to prevent neural tube defects. The most likely reason for this is:
A. folate is involved in action potential transmission from mother to fetus.
B. folate is directly involved in erythropoiesis.
C. folate is critical for proper development of the mesoderm.
D. folate plays a role in ectodermal induction.
D is correct. Neural tube defects are defects in the central nervous system. The nervous system is derived from the ectoderm. It can be concluded from the given information that folate is important for neurulation, or the induction of the ectoderm to differentiate into the nervous system.
In human females, mitotic divisions of oogonia that lead to formation of presumptive egg cells (primary oocytes) occur between:
A fertilization and birth only.
B fertilization and puberty only.
C birth and puberty only.
D puberty and menopause only.
The correct answer is A.
The question asks the examinee to identify the stages in the human female life cycle between which all the mitotic divisions that lead to primary oocyctes occur. These stages occur in the following order: fertilization, birth, puberty, menopause. All of the mitotic divisions that form primary oocytes occur prior to birth
An alternative method for examining the effects of fatty acids on blood flow would be to measure changes in blood pressure. If blood pressure were measured, one would predict that it would be lowest in which of the following?
A Heart
B Arteries
C Arterioles
D Capillaries
The correct answer is D.
An alternative method for examining the effects of fatty acids on blood flow would be to measure changes in blood pressure. It blood pressure were measured, one would predict that blood pressure would be lowest in the capillaries, as compared to the heart, arteries, or arterioles. Pressure would be even lower in the veins, but this option was not offered.
What is the primary function of the colon?
Its function is to reabsorb fluids and process waste products from the body and prepare for its elimination
Normally the immune system avoids attacking the tissues of its own body because:
A a special intracellular process recognizes only foreign antigens.
B the body does not make any antigens that the immune system could recognize.
C it changes its antibodies to be specific only to foreign antigens.
D it suppresses cells specific to the body’s own antigens.
Solution: The correct answer is D.
The immune system is designed to attack foreign material in the body. It avoids attacking tissues of its own body because it suppresses cells that are specific to its own body’s antigens (surface molecules that would otherwise initiate an immune response).
An ulcer that penetrated the wall of the intestine would allow the contents of the gastrointestinal tract to enter:
A the perineum.
B the peritoneal cavity.
C the pleural cavity.
D the lumen of the intestine.
Solution: The correct answer is B.
If an ulcer penetrated the walls of the intestine, this would allow the contents of the gastrointestinal tract to enter the peritoneal cavity. Membranes surround this cavity, which would prevent further transport of the gastrointestinal contents through the rest of the body. An ulcer in the small intestine would not allow the contents to enter the lumen because this is the normal place in which the contents are found.
In the ETC, Electrons are passed from carriers with _____ reduction potential to those with _____ reduction potential.
lower, higher
Which of the following is NOT considered an organic acid?
A. Folic acid
B. Carbonic acid
C. Ascorbic acid
D. Citric acid
B is correct. An organic compound must contain carbon and hydrogen in its formula. Furthermore, there must be a covalent bond between a carbon and hydrogen atom in the molecular structure. Organic acids are weak acids, generally having formulas of R-CO2H, with the acidic hydrogen bonded to an oxygen atom.
Even knowing this information, you may be intimidated, as you may not be familiar with the structures of all of these choices. However, you can begin with the most familiar compound, carbonic acid. The Lewis structure of this compound is shown below.
Conn’s syndrome, also known as primary hyperaldosteronism, is most likely to cause which symptom?
A. High renin concentration
B. Low blood potassium
C. Low blood sodium
D. Hypotension
B is correct. This question is asking you to recall the effects of aldosterone and how it achieves those effects. Aldosterone increases H2O and Na+ reabsorption from the kidney while exchanging K+ ions for Na+ ions
Viruses are directly involved in which of the following processes in bacteria?
A. Transformation
B. Conjugation
C. Transduction
D. Binary fission
C is correct. Transduction is a form of horizontal gene transfer in bacteria in which bacteriophages (viruses that infect bacteria) transmit genomic material.
In an adult, which of the following cell types is LEAST likely to enter a programmed G0 phase of the cell cycle?
A. Liver cells
B. Kidney cells
C. Epithelial cells
D. Neurons
C is correct. For this question, we need to know what the G0 phase (shown below along with the rest of the cell cycle) entails. This is the state that a cell will enter if it does not need to divide. Since epithelial cells are those that divide the most out of the options, choice C is correct.
What are the purines? What makes them special?
Purines have a 2 rings structure. They are Guanine and Adenine
What are the pyrimidines?
They only have 1 ring in their structure. They are Cytosine, Uracil, and Thymine (Remember CUT)
NADPH to NADP+ is what?
NADPH is oxidized to NADP+
The SN2 mechanism is favored by ______ solvents,
polar aprotic
What is the function of ligase during S-phase?
A. Begins synthesis of a new strand of copied DNA
B. Binds together pieces of the lagging strand
C. Repairs pieces of mis-replicated DNA
D. Opens the double helical strand of DNA to begin replication
B is correct. This question is asking us to simply recall a fact about the S-phase of a cell, aka DNA replication. You should know that DNA ligase is the enzyme that connects Okazaki fragments on the lagging strand of DNA being replicated. An overview of some of the key structures and enzymes of DNA replication is shown below.
Which of the following would be LEAST useful in cellular movement?
A. Flagella
B. Actin polymerization
C. Microtubule depolymerization
D. Cilia
C is correct. In order for cells to travel to the site of injury, they need to migrate. Microtubule de-polymerization is responsible for separating chromosomes during anaphase of mitosis or meiosis I or II. It does not contribute to overall cell migration.
Difference between nucleotide and nucleoside?
Nucleoside vs. Nucleotide. A nucleoside consists of a nitrogenous base covalently attached to a sugar (ribose or deoxyribose) but without the phosphate group. A nucleotide consists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups.
Phosphotase
class of hydrolase responsible for the cleavage of phosphate bonds utilizing water to remove a molecule of inorganic phosphate
Kinase
an enzyme that catalyzes the transfer of a phosphate group from ATP to a specified molecule.
What ribosome subunits do eukaryotes contain?
What ribosome subunits do prokaryotes contain?
