15. Bootcamp Qs Flashcards

Question

An animal cell was lysed, placed in a test tube, and centrifuged. Which organelle would pellet from the centrifuge first? ``` A. Ribosome B. Lysosome C. Mitochondria D. Golgi complex E. Nucleus ```

Answer 1

E. Nucleus - The nucleus is the largest and most dense organelle in the cell and will pellet first. - ribosomes would be expected to pellet out last due to their small density and size - Lysosome would be expected to pellet out after the nucleus, but before the smaller and less dense ribosomes.

Answer 2

E. 10^6 - In this problem, the scientist performed a three-step 1:100 dilution, meaning they diluted the original concentration first to 10^-2, then to 10^-4, and finally to 10^-6. The question asks for the dilution factor, which is the final volume divided by the original volume (or the inverse of the concentration)

Answer 3

A. Denature non-covalent bonds in a protein - Sodium dodecyl sulfate is a very strong anionic detergent that is used in gel electrophoresis to separate proteins based on their electrophoretic mobility (a function of the length of a protein and its charge). SDS is used to denature and linearize proteins and to impart a negative charge to the proteins. You could deduce it would impart a negative charge and not a positive one because sulfate is very negative and anionic. With this method, only the protein’s size and charge will be compared. Generally, all gel electrophoresis will denature a protein to compare its size - SDS (sodium dodecyl sulfate) has three primary effects on protein: Denatures the protein Linearizes the protein Adds negative charge to the protein The SDS-PAGE (polyacrylamide gel electrophoresis) is used to separate proteins on the basis of size (molecular weight). Smaller proteins will travel further than large proteins from the negative cathode to the positive anode.

Answer 4

D. Aquaporins - Aquaporins are protein structures in the membrane that help water passively flow into or out of the cell, a process known as facilitated diffusion.

Answer 5

C. Gametophyte

Answer 6

A. Flatworms - A coelom is a cavity lined by an epithelium derived from mesoderm. Mollusks have a reduced, but still true, coelom. A flatworm(also known as planarian) is an acoelomate because it does not have a coelom within its mesoderm layer. - Acoelomate: flatworms - Pseudocoelomate: roundworms - True coelomate: molluscs, annelids, arthropods, echinoderms, chordates

Answer 7

``` Diplo-: pairs Strep-: chain Staph-: grape-like clusters -coccus: spherical -bacillus: rod-like Spirilla/spirochetes: spirals ```

Answer 8

Mouth: salivary amylase (carbohydrates) Stomach: Pepsin (proteins) Pancreas: pancreatic amylase (carbohydrates), pancreatic trypsin and chymotrypsin (proteins), carboxypeptidase (proteins), nucleases (DNA, RNA), lipase (fats) [Note: these digestive enzymes are secreted by the pancreas but carry out their function in the small intestine] Small Intestine: Disaccharidases (carbohydrates), dipeptidases and aminopeptidases (proteins), nucleotidases (nucleotides), nucleosidases (nucleosides)

Answer 9

- FSH Follicle stimulating hormone Regulate development, growth, and reproduction. FSH helps develop a primary follicle. It acts synergistically with LH. - LH Luteinizing Hormone Regulate development, growth, and reproduction. Acute increase in LH triggers ovulation and develops corpus luteum. In males it stimulates Leydig cells to produce testosterone. It acts synergistically with FSH. - ACTH Adrenocorticotropic Hormone Stimulates adrenal cortex - TSH Thyroid-stimulating hormone Stimulates the thyroid - HGH Human growth hormone Regulates protein synthesis and cell division - Prolactin Prolactin Production of milk in mammary glands

Answer 10

C. Stimulate osteoblast activity - Two hormones regulate calcium levels in blood: calcitonin (produced by the thyroid), and parathyroid hormone (produced by the parathyroid). Calcitonin serves to lower calcium levels in blood. It does this by stimulating osteoblast activity, which builds up bone, which requires using calcium in the blood. Parathyroid hormone is the opposite, if calcium levels are too low in the blood, it will stimulate osteoclast activity to release calcium from the bones to the blood.

Answer 11

A. B cells - There are two parts to the immune system: specific and nonspecific defense. Specific defense responds to antigens, such as the toxin from an insect sting, or a molecule on the plasma membrane of a pathogen. Nonspecific defense is not specialized for a particular pathogen; it defends against all pathogens in general. Examples of nonspecific defenses include: skin, interferons, phagocytes, cilia, and lysozyme. Interferons are molecules secreted by cells invaded by viruses that stimulate other cells to help defend against viruses. Phagocytes are white blood cells that engulf pathogens. Cilia line the lungs and help sweep pathogens out of the lungs. Lysozyme is a protein that breaks down cell walls in bacteria. - The distinguishing characteristic of B cells is that they all possess a B cell receptor (BCR), which binds to specific antigens, making this answer correct. Formed in the bone marrow, B cells are important because they can differentiate into memory B cells, which can produce antibodies for pathogens that have already been encountered.

Answer 12

E. Capacitation - Capacitation refers to the increased flagella motility and destabilization of the acrosomal membrane seen in ejaculated sperm. Capacitation is a necessary step for a sperm to be able to penetrate an oocyte’s zona pellucida and fertilize the egg, so this answer is correct.

Answer 13

- Ectoderm: Epidermis of skin, hair, nails, nervous system, lens of eye, enamel of teeth - Mesoderm: Dermis of skin, muscle, skeleton, circulatory system, gonads, kidneys, respiratory tracts, notochord - Endoderm: Lining of digestive and layer of respiratory tracts, liver, pancreas

Answer 14

C. Pleiotropy - Pleiotropy occurs when a single gene has multiple phenotypic outcomes. In sickle-cell disease, a single mutation produces abnormal hemoglobin molecules. This results in damage to many organs and also results in several disorders. In contrast, polygenic inheritance is when many genes contribute to one phenotypic outcome. A great example is the height of humans, which is controlled by many genes and results in one phenotype. Epistasis occurs when one gene affects the expression of the second gene. - Epistasis describes when one gene affects the phenotypic expression of a second gene

Answer 15

A. Hypothalamus The hypothalamus controls the body’s temperature, hunger, thirst, sleep, and circadian cycles. One of its most important functions is that it links the nervous system to the endocrine system through the pituitary gland. The pons relays signals from the forebrain to the cerebellum. The medulla controls autonomic functions, such as respiration, digestion, and the pumping of the heart. The cerebral cortex is a complex portion of the brain that is involved in higher-level thinking and sensory perception. Lastly, the cerebellum is involved in motor control, such as balance and coordination.

Answer 16

D. closing of semilunar valves. When the heart contracts, the ventricles force blood through the semilunar valves and into our arteries. Also during this time, the AV valves are shut to prevent the blood from being forced back into the atriums. When the ventricles relax, the semilunar valves are shut to prevent backflow from the blood they just forced into the arteries, and the AV valves are reopened; this is called the diastole phase. The opening and closing of the AV valves and semilunar valves causes the “lub-dup” sounds in the heart. The ventricles contract during the systole phase of circulation, not the diastole phase; therefore the answer choice is incorrect. When the ventricles contract, the AV valves snap shut to prevent backflow of blood – this is responsible for the “lub” part of the “lub dub” sound in heart beats. When the ventricles contract, the AV valves snap shut to prevent backflow. The contraction of the ventricles is associated with the systole phase of circulation, not the diastole phase The aortic and pulmonary semilunar valves snap shut when the ventricles relax, to prevent backflow from the pulmonary artery and aorta. The relaxation of the ventricles is associated with the diastole phase of circulation, so the answer choice is correct. The closing of the semilunar valves is responsible for the “dub” part of the “lub dub” sound in heart beats.

Answer 17

E. Proteins In the kidney system, blood enters from an afferent arteriole into the glomerulus, where pressure forces water and solutes through the capillary walls into the Bowman’s capsule, like a sieve. Small particles can be pushed through the capillary walls, but red blood cells and proteins cannot pass through and remain in the blood. The filtrate in the Bowman’s capsule will then travel through the nephron, where the majority of salts, water, and glucose will be reabsorbed. Proteins are not able to filter through the fenestrations in the glomerulus into the Bowman’s capsule, so the answer choice is correct. The Bowman’s capsule and the glomerulus are both components of the renal corpuscle, which together with the renal tubule forms a nephron. Hydrostatic pressures force blood plasma through the fenestrations of the glomerulus – these fenestrations screen out blood cells and large proteins to prevent them from entering the Bowman’s capsule. Additionally, podocytes (cells in the Bowman’s capsule) further filter blood to prevent large molecules like protein from passing through, but allow smaller ones (including sugar, water, salts, vitamin, and nitrogen wastes).

Answer 18

C. Posterior pituitary and adrenal cortex The posterior pituitary releases ADH, which allows the kidneys to reabsorb more water. The adrenal cortex releases mineralocorticoids, such as aldosterone, which affects the kidney to increase salt reabsorption (which in turn increases water absorption as well due to changes in osmolarity). The pancreas releases glucagon (increase blood glucose) from alpha cells and insulin (decrease blood glucose) from beta cells. The thyroid controls general metabolism and releases calcitonin, which lowers blood calcium. The parathyroid releases PTH (parathyroid hormone), which increases blood calcium. The anterior pituitary releases FSH, LH, ACTH, TSH, prolactin, and growth hormone. The testes produce testosterone. The testes produce testosterone (that affect the testes themselves and have general effects on secondary sexual characteristics). The posterior pituitary stores antidiuretic hormone (ADH) and oxytocin produced by the hypothalamus; ADH targets the kidney, while oxytocin targets the mammary glands and uterus. These structures do not produce hormones that target the same organ The posterior pituitary stores antidiuretic hormone (ADH) and oxytocin produced by the hypothalamus; ADH targets the kidney, while oxytocin targets the mammary glands and uterus. The adrenal cortex produces glucocorticoids (such as cortisol) that affect the body on a general level to increase blood glucose, and mineralocorticoids (such as aldosterone) that target the kidney. Since the posterior pituitary produces ADH that targets the kidney, and the adrenal cortex produces a different hormone (aldosterone) that targets the kidney, the answer choice is correct. ADH increases reabsorption of water, while aldosterone increases reabsorption of Na+ and excretion of K+. The adrenal cortex produces glucocorticoids (such as cortisol) that affect the body on a general level to increase blood glucose, and mineralocorticoids (such as aldosterone) that target the kidney. The thyroid produces thyroxine (T4) and triiodothyronine (T3) which target the general metabolic rate of the body, and calcitonin which targets the bones.

Answer 19

B. Fats Cholecystokinin is a hormone produced by the small intestine in response to fats. It stimulates the gallbladder to release bile, which helps in the emulsification of fats, and stimulates the pancreas to release lipases. Gastrin is produced once the nervous system sees or smells food, which stimulates the stomach to produce gastric juices. Secretin is produced in the small intestine and stimulates the pancreas to produce bicarbonate to neutralize the acidity of the chyme. Cellulose does not stimulate the release of cholecystokinin; therefore the answer choice is incorrect. Cellulose cannot be broken down by the human digestive system, as we lack the necessary enzymes to break the beta-glucose linkages found in its polysaccharide structure. In ruminant digestive systems, cellulose is broken down by bacteria present.

Answer 20

D. diaphysis. The diaphysis is the name of the shaft of a long bone, which is made of compact bone. The epiphysis is the rounded end of a long bone. The metaphysis is the wider portion of a long bone situated near the epiphysis, this is where the majority of growth happens during puberty. The periosteum is a membrane that covers the surface of all bones, except at the joints of long bones. It provides nourishment and sensation to the bones. The medullary cavity is the central cavity of bone shafts. It usually contains red bone marrow, which produces blood cells, and yellow bone marrow, which consists of adipose tissue. The metaphysis is the area of long bone between the ends (epiphysis) and shaft (diaphysis); therefore the answer choice is incorrect. It contains the epiphyseal plate (or growth plate) where lengthening of the long bone occurs until adulthood, when the hyaline cartilage is replaced by bone and no further ossification occurs. The diaphysis refers to the shaft of the long bone, so the answer choice is correct. Yellow bone marrow can be found inside the diaphysis (which contains adipose cells for fat storage), as well as red bone marrow (where hematopoiesis aka red blood cell production occurs). Yellow bone marrow can be found in the medullary cavity (which contains adipose cells for fat storage), as well as red bone marrow (where red blood cell production occurs).

Answer 21

B. Mesoderm The notochord consists of cells on the surface of the mesoderm germ layer, which provides support in lower chordates. It is considered the first “backbone” in chordates. Ectoderm: Epidermis of skin, hair, nails, neural tube, lens of eye, enamel of teeth Mesoderm: Dermis of skin, muscle, skeleton, circulatory system, gonads, kidneys, respiratory tracts, notochord Endoderm: Lining of digestive and layer of respiratory tracts, liver, pancreas

Answer 22

A. Revert a somatic cell into a totipotent state. Cloning is the process of taking a somatic cell from an animal and producing a genetic copy from that cell. It is different from fertilization in that there is no genetic variation; each clone is a genetic replica of the parent animal. This was best characterized by Dolly, the cloned sheep. Somatic cells contain the full genome of an organism, but are usually specialized based on the tissue they are a part of. In contrast, totipotent cells can give rise to any and all human cells, and even an entire functional organism. To clone an animal with this method, a somatic cell would need to be reverted to its less specialized totipotent state such that it could give rise to a new, genetically identical animal. Somatic cells contain the full genome of an organism, but are usually specialized based on the tissue they are a part of. In contrast, totipotent cells can give rise to any and all human cells, and even an entire functional organism. To clone an animal with this method, a somatic cell would need to be reverted to its less specialized totipotent state such that it could give rise to a new, genetically identical animal. Totipotent: - This describes a single cell with the ability to divide and produce an entire organism. Can also produce extraembryonic membranes. - A zygote, up to a morula, consists of totipotent cells. Any one of these cells can produce an entire organism. Pluripotent: - A stem cell that can differentiate into any of the three germ layers: endoderm, mesoderm, or ectoderm. - They can give rise to any cell type, but they cannot develop an entire organism because they cannot develop extraembryonic tissue, like the placenta.

Answer 23

E. DNA microarray ELISA is a technology to determine if a specific antigen exists. Antibodies are placed into a microtiter plate, and if they bind to their specific antigen there will be a color change in the microtiter plate, indicating that a specific antigen exists. Gel electrophoresis is a technique to separate macromolecules (DNA, RNA, proteins) by size and charge. Shorter macromolecules will move faster than longer macromolecules and travel further. Karyotyping is a useful tool to count the number of chromosomes in a cell. This is useful in the diagnosis of trisomy diseases, or an abnormal number of chromosomes.

Answer 24

C. Binary fission Binary fission is a form of asexual reproduction in prokaryotes and some organelles within eukaryotes (mitochondria and chloroplasts). The DNA is duplicated and then the two copies migrate to opposite sides of the cell, and the cell then splits into two. The consequence of this is that all the bacteria and progeny are genetically identical. There are numerous ways we can force bacteria to uptake new DNA. Plasmids are short, circular DNA molecules outside of the main chromosome. Placing the bacteria in a solution of CaCl2 and heat will force the bacteria to uptake plasmids and incorporate them into their genome, this process is a form of transformation. A brief pulse of high voltage electricity in a solution of bacteria will force them to open their pores and allow for plasmids to enter the bacteria as well. This process is known as electroporation. Notice the root words “electro-” and “-poration”. You can guess it has something to do with electricity and pores in the membrane. Transduction is the process of introducing new DNA through a bacteriophage, or virus. A virus carrying bacterial DNA injects that DNA into a host bacterium, and the DNA is then incorporated into the host genome. Conjugation is the transfer of genetic material between two bacterial cells by cell-to-cell contact. The donor bacterium forms a pilus to connect to the recipient bacterium. The donor then sends DNA to the recipient, who can incorporate it into their genome

Answer 25

B. Helicase At the beginning of replication, helicase unzips the DNA to produce a replication fork. The replication fork is held in place by single-strand binding proteins. As helicase unwinds the DNA upstream, further downstream the DNA actually becomes positively supercoiled. Topoisomerase removes these twists and knots induced by helicase. Telomerase is an enzyme that extends the template strand to add a short sequence of nucleotides to the replicated strand. This is because eukaryotes have linear DNA molecules and cannot replicate the ends of the original DNA, because no primer can be placed.

Answer 26

D. rainfall and temperature Biomes are classified based on the biological effects of temperature and rainfall on vegetation. The majority of biomes are dependent on these two factors. For example, deserts have a lack of rainfall and very high temperatures, giving them their characteristics. In contrast, rainforests have lots of rainfall and warm temperatures, providing an environment for a biologically diverse biome. Many descriptions you see on biomes will have a chart displaying their average temperature and rainfall throughout the year.

Answer 27

A. The phylogenetic tree that has the least amount of assumptions is the most preferred. The law of parsimony, or Occam’s Razor, says that when choosing between competing hypotheses, the one that makes the least amount of assumptions is the most preferred. Another way to say it is that the simplest explanation is probably the most accurate. When developing phylogenetic trees, the tree that explains the evolution of organisms with the least amount of assumptions is most likely the correct one. Homoplasy, also known as convergent evolution, is a phenomenon that describes when two distinct clades develop strikingly similar characteristics despite the fact that there is no common ancestor with the trait. A well-known example of this is the convergent evolution of wings in both birds and bats. Rather than making it easy to develop phylogenetic trees, this tends to confound attempts to make them. For instance, imagine a phylogenetic tree where flight was viewed as the most important characteristic. This would lead you to determine that birds and bats are the most closely related of all vertebrates, which is simply not true.

Answer 28

B. Membrane glycoproteins Clathrin is a protein that forms intracellular coats during receptor mediated endocytosis. This has nothing to do with cellular recognition. Clathrin is a protein which aids in receptor mediated endocytosis. Endocytosis is when the cell membrane forms a vesicle (a package that is surrounded by plasma membrane) around something extracellular that the cell wants to internalize. When a membrane receptor binds certain substrates that the cell wants to internalize, the receptor signals for clathrin lattice formation. Clathrin forms a lattice around the incoming vesicle in pits, and this is known as a clathrin coated pit. Clathrin coating occurs intracellularly and has nothing to do directly with cell recognition. While all cells have a resting membrane potential, only nerve and muscle cells are considered excitable cells – excitable cells are cells that can fire an action potential.

Answer 29

C. Steroid hormones are nonpolar and require a protein carrier to shield them from polar blood Steroid hormones do not require transmembrane channels, they diffuse directly through the cellular membrane. Hormones are only able to activate cells that produce a receptor for that hormone. This is how hormones are able to activate only certain cell types, even though they come into contact with a huge variety of cells during circulation. Hormones will not activate nontarget cells because nontarget cells will not produce a receptor to that hormone. The amount of dissolved oxygen in the blood plasma is very small as most oxygen is transported inside red blood cells bound to hemoglobin. Additionally, even if there was sufficient oxygen dissolved in the cell, oxygen would oxidize agents, not reduce them.

Answer 30

C. p53 failing to activate Tumor suppressor genes require two mutated alleles in order to have loss of function (cancer-causing) p53 is the tumor suppressor guardian of the cell; its failure to activate will encourage cancer. Proto-oncogenes are the normal, noncancerous state of genes which regulate growth and division. Reactive oxygen species (ROS) like hydrogen peroxide (H2O2) damage DNA and increase the rate of DNA mutations. A decrease in ROS would lower risk of developing cancer. Tumor suppressor genes make protein products that protect the cell from cancer (tumor suppressor gene products will suppress tumors). A loss of that protective function causes cancer. Tumor suppressor genes cause cancer through a loss of function mutation. Tumor suppressor gene mutations are recessive: a cell would have to lose function in both of its tumor suppressor genes in order to lose function. This is because tumor suppressor genes are haplosufficient. One tumor suppressor gene has sufficient function to produce enough protein to have a tumor suppressor effect. Tumor suppressor genes follow a ‘two hit hypothesis’, meaning that mutations are required in both of their genes in order to be cancer-causing.

Answer 31

- p53 - p21: p21 is a cyclin dependent kinase (CDK) inhibitor. If p21 inhibits CDK, then p21 prevents cell division. Increasing the activity of p21 will increase the amount of inhibition of CDK, and p21 will decrease the amount of cell division. Another tumor suppressor which has come up before on the DAT is retinoblastoma protein abbreviated rb. Being a tumor suppressor, it follows the two-hit hypothesis of inactivation (both copies mutated in order to cause cancer)

Answer 32

Proto-oncogenes are the genes that regulate growth function within the cell. A proto-oncogene is the noncancerous version of the gene that has a regular and an important role within the cell. Proto-oncogenes affect different processes such as cell growth and differentiation – but if these processes go awry, this will lead to cancer. Proto-oncogene → mutation → oncogene Oncogenes are the altered allele version of the proto-oncogene, where the ‘regulation of growth function’ has been dysregulated. The oncogene can cause cancer through a gain of function mutation (gain of growth). It only takes one copy of a gain of function mutation in an oncogene to cause cancer. Contrast this with tumor suppressor genes which cause cancer through a loss of function mutation, and require both copies to have loss of function mutations in order to be cancer causing. Oncogenes either make too much protein product or they make a protein product that is too active. These changes represent a gain in function, which causes the cell to become cancerous.

Answer 33

E. I, II, and III The sedimentation rate of a particle in a centrifuge tube will increase as the object increases in mass and density and as the shape becomes more compact. Therefore, all three of these features in the answer choice influence how a cell lysate is separated in centrifugation. If a scientist wants to isolate a specific component of the cell within a sample of cells, the various components of the cell can be separated out through centrifugation. First, the cells must be split open so that the components can be separated. This process is called homogenization, and is accomplished with a lab blender, or shear forces. The homogenate is the mixture of the split open cells, and is stored in an inert buffer to preserve the cell components. A centrifuge spins the homogenate at very high speeds, in a circular path. The higher mass, denser, more compactly shaped particles will sediment to the bottom of the centrifuge tube, and this is known as the pellet. Whatever is not in the pellet is the ‘remainder on top’ and this is referred to as the supernatant. The centrifugation process is repeated over and over to gradually separate out the different components of the cell. Cells and the nucleus come first, then dense organelles, then ribosomes and cytosol. The fractionated (isolated) components of the cell can then be studied. It was previously thought that only proteins worked as enzymes catalyzing reactions. However, more recent research has shown that some types of RNA is also capable of catalysis. Ribozymes are RNA molecules that can perform biological catalysis in the same manner as protein enzymes.

Answer 34

C. assist newly synthesized proteins in correct folding Chaperonins are proteins found in both prokaryotic and eukaryotic cells. Chaperonins assist newly synthesized polypeptides to fold into their correct shape. Clathrin is a protein which aids in receptor mediated endocytosis. When a membrane receptor binds certain substrates that the cell wants to internalize, the receptor signals for clathrin lattice formation. Clathrin forms a lattice around the incoming vesicle in pits, and this is known as a clathrin coated pit. Clathrin coating occurs intracellularly and has nothing to do directly with cell recognition. [E]: Lysosomes are cellular organelles which contain acidic, hydrolytic enzymes. They assist the cell in digestion.

Answer 35

D. Glycolysis, pyruvate decarboxylation, citric acid cycle Pyruvate decarboxylation is the step of cellular respiration that takes the 3 carbon pyruvate generated during glycolysis and processes that pyruvate to form a 2 carbon acetyl CoA, CO2, and NADH. For every acetyl CoA, Krebs cycle produces 2 CO2, 3 NADH, 1 FADH2, and 1 ATP. So for every two acetyl CoA that enters the Krebs cycle: 4 CO2, 6 NADH, 2 FADH2, and 2 ATP are produced.

Answer 36

C. Endocrine Paracrine signaling is when a cell signals to other cells in its surrounding vicinity. Examples include blood clotting factors and tissue healing. Neuronal signaling is direct communication between neurons via the use of neurotransmitters being sent across a synapse. Endocrine signaling is when hormones are secreted into the blood vasculature, and travel throughout the body. The hormone will be recognized and received by any cell that has a complementary target receptor. The sympathetic nervous system directly stimulates the adrenal medulla. The adrenal medulla then releases epinephrine (adrenaline) and norepinephrine (noradrenaline) into the blood. Epinephrine and norepinephrine will travel through the blood and act on any cell that has complementary adrenergic receptors. Exocrine hormones are secreted from glands through a duct. Examples include sweat, salivary, mammary glands, and some of the pancreas and liver function. Autocrine glands send extracellular signals to themselves. White blood cells are a common example of autocrine stimulation, as they release factors that stimulate themselves.

Answer 37

D. Vasoconstriction will increase total peripheral resistance If blood pressure is low, antidiuretic hormone is produced and released to increased blood volume/pressure Renin converts angiotensinogen to angiotensin I. Angiotensin converting enzyme converts angiotensin I to angiotensin II. When blood pressure is low, angiotensin II levels increase, which increases levels of circulating aldosterone. This increases the amount of salt that is reabsorbed in the nephron, and therefore increases the amount of circulating salt. When blood pressure is low, antidiuretic hormone (ADH) is released in order to preserve fluids. ADH helps us to reabsorb more water in the collecting duct of the nephrons, limiting how much we pee out. If we have more body water, blood volume increases. Higher blood volume = higher blood pressure.

Answer 38

– It stimulates additional aldosterone release from the adrenal gland cortex (so aldosterone levels increase). – It increases Na+ reabsorption from the proximal tubule (and water will follow the salt). – It is a potent systemic vasoconstrictor – causing vessels to constrict, thereby increasing total peripheral resistance (TPR). – It makes the individual more thirsty – so they drink more and increase their blood liquid volume (increasing TPR). Aldosterone is considered a mineralocorticoid hormone, and is produced by the adrenal cortex. Aldosterone functions to increase salt and water reabsorption, as well as potassium secretion in the distal tubules and collecting duct of the kidneys.

Answer 39

Heart rate is how fast the heart beats. Stroke volume is the volume of blood that is pumped out of the heart with each beat. Mean arterial blood pressure (MAP) is calculated from the cardiac output (CO) of the heart and the total peripheral resistance (TPR) of the vessels. MAP = CO x TPR MAP = (HR x SV) x TPR So increasing either the rate at which the heart beats, the volume of blood the heart pumps, or the total peripheral resistance in the vessels will increase the blood pressure. And we can increase TPR by constricting our blood vessels – making the diameter of the lumen of the vessel smaller (dilating the blood vessels would decrease TPR).

Answer 40

non-neuronal cells in the nervous system that nourish, support, and protect the neurons and make to ensure the conditions are perfect for neuronal health. There are two subcategories of glial cells: microglia and macroglia. Microglial cells are the defenders of the CNS. They are specialized macrophages which protect the CNS. Macroglia can be further broken down into subtypes. The most important points about macroglia for DAT purposes are: Schwann cells: these are the cells that form myelin sheath in the peripheral nervous system. Oligodendrocytes: form the insulating myelin sheath in the central nervous system. Astrocytes: the most abundant type of glial cell. They help provide blood supply to CNS neuron, recycle neurotransmitters, and maintain proper ion levels. They also help to form the very important Blood-Brain-Barrier – a barrier which helps ensure the brain’s cerebrospinal fluid (CSF) has unique, specific composition compared to composition of blood. Satellite cells: have similar function to astrocytes, but satellite cells function in the PNS. Ependymal cells: they create the cerebrospinal fluid which bathes the spinal cord and the brain.

Answer 41

D. stimulating translocation of vesicles containing glucose transporters to the cellular membrane Steroid hormone bind to receptors in the nucleus and act as transcription factors. Insulin is a protein hormone that binds to an insulin receptor tyrosine kinase on the cell surface Glucose is a large molecule and cannot diffuse through the phospholipid bilayer. Insulin has no effect on this. Insulin stimulates premade vesicles (membrane bound packages) of glucose transporter to translocate and fuse with the membrane. This increases the cell’s efficiency at bringing glucose into the cell. Pyrogens are hormones that causes the hypothalamus to increase the body’s temperature.

Answer 42

D. Exposed collagen in damaged blood vessels activates platelets Platelets are cell fragments, and do not contain a nucleus (anucleate). RBCs are also anucleate. Thrombin is protease which converts circulating fibrinogen in the blood into long strands of the protein fibrin. Fibrin accumulates with platelets to form a blood clot. Megakaryocytes are large bone marrow cells that are the precursor to platelets. When a blood vessel is damaged, collagen fibers from the blood vessel wall that previously were internal are now exposed to the blood circulating through that vessel. Platelets that are circulating past this area are activated and bind. This begins the coagulation cascade. Vitamin K is an important cofactor for some of the clotting factors in the clotting cascade. However, it does not form the clot itself – it is just a cofactor.

Answer 43

a. Tissue is damaged. This tears blood vessel walls which exposes collagen that is within the wall. b. Exposed collagen in the circulating blood causes the platelet activation and platelets begin to adhere and aggregate in the area of the blood vessel where the rip has occurred. This forms a platelet plug. c. Activated platelets release thromboplastin (also known as tissue factor). Thromboplastin converts the precursor (inactive) prothrombin into its active form, thrombin. d. Activated thrombin converts precursor fibrinogen to fibrin. Fibrin strands polymerize with other fibrin strands, and attach to platelets to form a blood clot (hemostatic plug). Mnemonic: PTPT, TFF Mnemonic: P(platelets) T(Thromboblastin) P (Prothrombin) T(Thrombin) T (Thrombin) F (Fibrinogen) F (Fibrin)

Answer 44

Megakaryocytes

Answer 45

D. It can receive genes via transformation

Answer 46

D. Mollusca Coelom is a fluid filled body cavity that has a lining derived from the mesodermal layer. The mesodermal lining of the coelom is known as the peritoneum.

Answer 47

PR…ivileged… – PoRifera Ch…ildren – Cn…idarian (Ch looks like Cn) PLAY – PLAtYhelminthes Nicely – Nematoda (only one N in the mnemonic) ANd – ANNelida Maturely – Mollusca (only one M in the mnemonic) ARTHur – ARTHropoda Ensures – Echinodermata (only one E in the mnemonic) Cooperation – CHOrdata Everything before Nematoda is acoelomate (lack a coelom). Everything after Nematoda is coelomate (contains a coelom). Nematoda are considered pseudocoelomate (‘fake’ coelomate). Pseudocoelom is a body cavity that does not contain a full peritoneum. This pseudocoelom helps with nematode motility – they use the pseudocoelom as a hydrostatic skeleton. A hydroskeleton provides rigidity through fluid pressure.

Answer 48

E. Taiga-boreal forest The taiga-boreal forest is the largest terrestrial biome, characterized by cold winters (it has a far northern latitude) and coniferous (cone bearing) trees. The tundra is far North, with very little precipitation and permafrost (a layer of permanently frozen soil). There is a short growing season, and low biotic diversity. Deciduous forest goes through four different seasons. The leaves of trees change color in the autumn season and fall to the ground- this is what defines ‘deciduous’. Because of falling leaves, the soil has rich organic matter. There is vertical stratification of species – meaning different species exist at different altitudes (ground, in the branches of trees, and at the tops of trees). Temperate grasslands are large, rolling hills of grass and flowers. There are very few trees and little rainfall. There are two main seasons: growing season and a dormant season. During the dormant season it becomes too cold and the ground too hard for anything to grow.

Answer 49

B. Palms Sebaceous glands are tiny glands in the skin that secrete an oil called sebum. They are located in the dermis of the skin and found nearly everywhere in human skin EXCEPT for the palms of the hands and soles of the feet. The body releases this oil to waterproof and protect the skin, but it also is a lipid and reduces friction. It doesn’t make sense to make your hands and feet slippery, so we can infer this must be the correct answer. The palms of the hands (as well as soles of the feet) are the only areas of the body that do not contain sebaceous glands, so the answer choice is correct. Sebaceous glands produce oil (sebum) and are connected to hair follicles (of the answer choices listed, only the palms lack any hair follicles). The oil of sebaceous glands keeps the skin relatively acidic to discourage microbial growth. When these glands become plugged, acne results.

Answer 50

B. Supply nutrients and nerve function in compact bone A long bone is made of dense compact bone (cortical bone) on the outside and cancellous bone on the inside (less dense bone). The dense compact bone still needs nutrients and nerve function, and Haversian canals provide this function by having little tubes running parallel to the axis of the long bone. The Haversian canals house blood vessels, nerves, and lymphatic vessels. Cancellous bone, also known as spongy bone, is less dense and houses red bone marrow and yellow bone marrow. Red bone marrow produces erythrocytes (red blood cells), platelets, and white blood cells. The periosteum surrounds the outer surface of all bones and provides nutrients. Haversian canals are formed when osteoclasts burrow tunnels through the bone. It is osteoblasts that form the dense lamellae to support the bone; therefore the answer choice is incorrect. After osteoclasts have burrowed tunnels forming the Haversian canals, osteoblasts lay down new matrix onto tunnel walls forming the concentric rings that are the lamellae.

Answer 51

C. SA node The sinoatrial node, or SA node, initiates the contraction of the heart and is known as the cardiac pacemaker. The SA node is located in the upper right atrium of the heart. It contracts the atria to fill the ventricles with blood and sends a delayed signal to stimulate the atrioventricular node, or AV node. The AV node sends an impulse through the bundle of His and Purkinje fibers, which results in the contraction of the ventricles. The vagus nerve is a cranial nerve that functions in parasympathetic activities. (you go to vegas, I don't feel bad for you) The Purkinje fibers – located in the walls of the ventricles – receives the impulse from the bundle of His and in turn causes contraction of both ventricles.

Answer 52

E. Macrophages. Macrophages can act as either non-specific or specific phagocytes. In non-specific defense, they engulf pathogens by phagocytosis. In specific defense, they engulf antibody-coated antigens by phagocytosis. Major histocompatibility complex II, or MHC II, and B cells are only used in specific immunity. Lysozyme is involved only in non-specific defense as an anti-bacterial enzyme. Helper T cells are lymphocytes that originate in the bone marrow like B cells, but mature in the thymus (hence why they’re called T cells). They have antigen receptors on their surface and only used in specific immunity. The stomach is where digestion of proteins begins in humans, via the digestive enzyme pepsin that breaks proteins down into smaller polypeptides for further digestion. While digestion takes place in the small intestine, the majority of it occurs in the duodenum – the jejunum and ileum primarily act in absorption.

Answer 53

B. end of inhalation. During inhalation our diaphragm contracts and therefore the volume in our lungs increases. This increase in volume leads to a decrease in pressure, which causes air to flow into our lungs. At the very end of inhalation is the point where we cannot breathe in anymore because our intrapleural pressure reaches its maximum negative value. During exhalation we relax our diaphragm, the volume of the lungs decreases, and air is pushed out of our lungs. Intrapleural pressure is the pressure within the pleural space (the fluid filled space between the double layered membranes covering the lungs). It is negative relative to the atmospheric pressure. When a person breathes in, the diaphragm contracts and the lungs expand, causing the intrapleural pressure to become more negative. At the end of inhalation (peak expansion of the lungs), the intrapleural pressure is most negative, so the answer choice is correct. As exhalation begins, the diaphragm relaxes and lung volume decreases, causing the intrapleural pressure to rise (become less negative).

Answer 54

ADH, or vasopressin, is produced by the hypothalamus and released by the posterior pituitary. It allows the collecting duct of the nephron to become more permeable to water, and as a result more water is reabsorbed from the filtrate. If more water is reabsorbed, then the remaining filtrate will become more concentrated, or have a higher osmolarity. When there is excess water in the body, the posterior pituitary secretes less ADH (there is less need to reabsorb water). Secreting less ADH would lead to a more dilute urine since the body is already well hydrated. Cortisol is a glucocorticoid released in response to stress. Cortisol provides several functions, including increasing blood glucose, suppressing the immune system, and aids in metabolism.

Answer 55

A. Acetylation DNA is coiled around histones in eukaryotes and some Archaea. The combination of DNA and histones is called a nucleosome. Recall that DNA has a slight negative charge. If we attach methyl groups to the histone, we will make the histone more positively charged. This will attract the negatively charged DNA more, and will bind the DNA to the histone tighter, decreasing transcription. If we add acetyl groups to the histones, we would make the histone groups more negative, and they would repel the negatively charged DNA to make the DNA more accessible, thus there will be more transcription and more expression of the gene. RNA interference is a method of gene control where siRNAs will degrade mRNA, which will decrease the expression of a gene. Heterochromatin is tightly packed DNA that consists of genes not transcribed. On the other hand, euchromatin consists of more “open” DNA that is transcribed and expressed.

Answer 56

B. Acts as a transcription factor Lipid hormones are small and nonpolar, and can diffuse through the cell membrane. If they bind to a cytosolic or nuclear intracellular receptor, it will translocate to the nucleus (if it is not already bound to DNA) and activate gene transcription as a transcription factor.

Answer 57

B. In CAM plants, the initial enzyme that fixes CO2 fixes the CO2 into a four carbon molecule

Answer 58

C. Phosphatase Kinases add phosphate to their substrate. Helicase ‘unzips’ the DNA double helix. A phosphatase is an enzyme which cleaves phosphate off of a substrate. Topoisomerase prevents ‘tangles’ as the DNA helix is being unwound. It relieves this stress by creating ‘nicks’ in the backbone. Ligase will ‘glue’ or ligate two unattached pieces of nucleic acid together.

Answer 59

D. Mitochondrial matrix FADH2 is produced during the Krebs cycle which occurs in the mitochondrial matrix. Glycolysis occurs in the cell cytosol. Glycolysis does generate NADH, but not FADH2. The mitochondrial matrix is the viscous fluid in the ‘inside’ of the mitochondria, which contains the mitochondrial DNA, ribosomes, and some enzymes. Pyruvate decarboxylation is the step of cellular respiration that takes the 3 carbon pyruvate generated during glycolysis and process that pyruvate to form a 2 carbon acetyl CoA, CO2, and NADH. Pyruvate decarboxylation also occurs in the mitochondrial matrix.

Answer 60

B. Helix-turn-helix motif The four common structural motifs seen in regulatory proteins that bind to nucleic acids are: Zinc-finger motif Leucine-zipper motif Helix-turn-helix motif Helix-loop-helix motif These are ‘structural’ components that occur again and again in the regulatory proteins that bind to nucleic acids. For the purposes of the DAT, being familiar with their names and their function (they are structural components seen in proteins that bind DNA) is sufficient.

Answer 61

D. has an activation energy requirement Even though there is a net release of energy, all reactions require some energy of activation. In thermodynamics, work is equal to energy. Exergonic reactions release energy, so exergonic reactions do work on the environment. Endergonic reactions absorb work from the environment.

Answer 62

B. produces acetyl CoA which enters Krebs cycle

Answer 63

B. The main white blood cell types in lymph are neutrophils, and macrophages The main white blood cell types in the lymphatic system are the lymphocytes; lymphocytes are T cells and B cells The lymphatic system relies on both smooth muscles in the vessels and contraction of the vessels by adjacent skeletal muscle in order to be propelled The lymphatic system contains valves, which ensure that lymph (the fluid that circulates through the lymphatic system) moves in a unidirectional, ‘forward’ direction. This is important, as the lymphatic system has no central pump (it is not ‘pumped’ by the heart, like the blood circulatory system is), and is a low pressure system. This is similar to veins, which have valves to ensure unidirectional flow, for the same reason (low pressure system). Remember, the lymphatic system is a low pressure system, and there is no pump. Lymph moves in the ‘forwards’ direction both by the contraction of smooth muscle in the walls of the lymphatic vessels AND by contraction of skeletal muscle that is adjacent to the lymphatic vessels. When the adjacent skeletal muscle is flexing (for example, think of a bicep flexing), it creates pressure in the area, which causes the lymph to be pushed forwards (and remember, it can only travel one way because of the unidirectional valves).

Answer 64

B. an inactive form of a protease A zymogen is the inactive precursor of an enzyme. Trypsinogen is the inactive form of trypsin which is a protease in the GI tract. When food enters the duodenum, glands in the duodenum release enteropeptidase. Trypsinogen is activated by entereopeptidase to active trypsin. Active trypsin then cleaves chymotrypsinogen to form the activated chymotrypsin. When a food bolus enters the stomach, the stomach is distended (stretched). This stretching is a signal for G cells of the stomach to release gastrin. Gastrin is a hormone which stimulates parietal cells of the stomach lining to release gastric juice (very acidic solution with high hydrochloric acid). Gastrin also stimulates chief cells of the stomach lining to secrete pepsinogen. Pepsinogen is a zymogen. Secretin is a hormone released by the duodenum in response to highly acidic gastric juice entering into the small intestine. Secretin causes the pancreas to secrete bicarbonate (HCO3–) into the duodenum. Bicarbonate is alkaline (basic) and will neutralize the acidic gastric juice that has entered the small intestine by way of the stomach.

Answer 65

major inhibitory NT in the body. It generates an inhibitory effect by opening ion channels that allow more chloride (Cl–) into the neuron and/or potassium ions (K+) out of the neuron. Because chloride is a negatively charged ion, if chloride enters the neuronal cell, the cell will become more negative; because potassium is a positively charged ion, if potassium leaves the neuronal cell, the cell will become more negative. If the neuron becomes more negatively charged, it is less likely to fire an action potential, ie. It is inhibited.

Answer 66

C. Type O Another blood cell surface protein is the Rhesus factor (Rh). You either have the Rh or do not have the Rh. So you are either Rh positive (+) or Rh negative (-). This is where (+) and (-) designations in blood typing come from, eg. my blood type is B+ (B positive). If a donor is Rh+ they cannot donate to someone who is Rh- as the Rh+ donor has Rh antigens on the blood cell surface. The universal donor (donor who can donate to anyone) is O-. O blood type has neither A nor B surface antigens, and O negative blood also does not have an Rh surface antigen. This means there are no blood cell surface antigens that would stimulate immune clearance. The universal acceptor is AB+. Because an AB+ person has both A and B cell surface antigens, as well as an Rh surface antigen, they can receive any blood type and not mount an immune response Any blood cell surface antigen they receive would be something their blood cells already have.

Answer 67

E. Antibodies Innate immunity is the body’s first line of defense, and is a nonspecific response. Innate immunity continues with the inflammatory response. There are five signs associated with inflammation: heat, redness, swelling, loss of function, and pain. Inflammation is associated with certain innate immune response cells like neutrophils, monocytes/macrophages, eosinophils, and basophils/mast cells Inflammation is associated with certain innate immune response cells like neutrophils, monocytes/macrophages, eosinophils, and basophils/mast cells While the innate immune response is nonspecific, the adaptive immune response is specific.

Answer 68

Never Let Monkeys Eat Bananas Never = Neutrophils Let = Lymphocytes (Natural Killer, T cells, B cells) Monkeys = Monocytes/macrophages Eat = Eosinophils Bananas = Basophils (which form mast cells)

Answer 69

The adaptive immunity lymphocytes are B cells and T cells. They are both produced in the bone marrow from blood stem cells. B cells mature in the bone marrow, while T cells travel to the thymus to mature.

Answer 70

D. It is a site of digestion in Annelida The gizzard is the site of mechanical digestion in a group of animals, including the annelida (earth worm). The gizzard is part of the digestive tract that has muscular walls which function to pulverize food. Often the food is mixed with other organic matter like soil that aids in breaking down (digesting) food.

Answer 71

B. The blastodisc The inner cell mass is the bilaminar part of the mammalian blastula that will form the actual embryo. The blastodisc is the bilaminar part of the bird, reptile, and fish embryo that will form the actual embryo. The zona pellucida is the mammalian equivalent to the vitelline layer of the sea urchin. This is a glycoprotein layer that is on the exterior of the egg, which helps bind sperm during fertilization. The primitive streak is the site of gastrulation. Mammalian embryos also have a primitive streak that forms within the inner cell mass. The allantois is an extraembryonic membrane, and aids in gas exchange for the embryo.

Answer 72

C. All organisms that live in one location An ecosystem represents all the organisms in one location (community) and the abiotic factors that interact with them.

Answer 73

C. Sigma factor Sigma factor binds to core RNA polymerase to form RNA polymerase holoenzyme. Sigma factor makes prokaryotic RNA polymerase have more specific binding to promoter regions. Prokaryotic RNA polymerase holoenzyme is the combination core RNA polymerase with sigma factor. Prokaryotic core RNA polymerase is able to bind to prokaryotic DNA, but it lacks the ability to target promoter sites that are upstream of the gene to be transcribed. Prokaryotic core RNA polymerase will combine with sigma factor to form RNA polymerase holoenzyme. The sigma factor provides RNA polymerase holoenzyme the ability to target the promoter region of bacterial DNA.

Answer 74

C. induce apoptosis in cancerous cells Natural killer cells are part of the innate immune system. The innate immune system has no immunological memory. Natural killer cells are part of the innate immune system, whereas cytotoxic T cells are part of the adaptive immune response. The innate immune system is quicker acting as it does not require activation. The adaptive immune system requires activation, and this means it is slower to begin acting Natural killer cells defensive actions include creating holes in the cellular membrane of its target, which causes target cells lysis, and inducing apoptosis (programmed cell death) in rapidly dividing cells. Monocytes are the precursor cells to macrophages. Basophils, mast cells, and eosinophils contain high amounts of cytoplasmic histsamine. While the innate immune response is nonspecific, the adaptive immune response is specific. The innate immune response is a generalized approach whereas the adaptive immune response is a targeted approach.

Answer 75

Innate immunity lymphocytes: Natural killer cells. Adaptive immunity lymphocytes: B and T cells Natural killer cells (NK) are part of the innate immunity, and share many similarities to cytotoxic T cells (CD8) which are part of the adaptive immunity. As the adaptive immune system requires activation, but the innate immune system is always ‘on’, NK cells are often the first to act, and CD8 cells will come in to help once the adaptive immunity has been stimulated. NK cells therefore have a speed advantage as they don’t need to be activated before they can do their job. However, CD8 cells have a specificity advantage, and will be more targeted as they have been activated to the specific antigen.

Answer 76

Eosinophil cell cytoplasm are filled with granules, and eosinophils are granulocytes. Eosinophils contain a variety of proteins that are damaging to both pathogens as well as host tissues. Eosinophils are important in fighting parasites. Two important proteins to remember that are found in eosinophils are major basic protein, and eosinophil cationic protein.

Answer 77

Like eosinophils, basophils/mast cells are granulocytes. The cell cytoplasm of these cells is filled with granules that can be released through degranulation. These cells are also packed with histamine as well as heparin, and are important mediators of inflammation/the allergic response. Histamine causes vasodilation, and heparin helps to prevent clots from forming – both of which promote more blood entry. Basophils leave bone marrow as mature cells and remain circulating in the blood, whereas mast cells leave the bone marrow and circulate the blood as immature cells, only maturing when they enter the tissue.

Answer 78

E. Hydrophobic interactions Hydrophobic interactions are only found in tertiary structure but not secondary structure.

Answer 79

A. The protein passes through the membrane seven times Receptor tyrosine kinases are single transmembrane – they only pass through the membrane once. They also bind hormones and cytokines. Phosphatases remove phosphate. Phosphorylation of the receptor tyrosine kinases activates a receptor tyrosine kinase, and therefore a phosphatase inactivates it. The receptor tyrosine kinase has an extracellular ligand binding domain. One of the defining traits of G protein coupled receptors (GPCRs) is that they are seven transmembrane (meaning the GPCR protein passes back and forth through the membrane seven times). Receptor tyrosine kinases are single transmembrane – they only pass through the membrane once.

Answer 80

C. Phase contrast microscopy

Answer 81

B. Cochlea The cochlea is the ‘snail shaped’ portion of the ear which is responsible for the signal transduction (converting one signal into another type of signal) of auditory waves into a signal to the brain. The semicircular canals are fluid containing canals whicih give the brain information about motion. The oval window is the entrance for the sound waves to the cochlea.

Answer 82

D. Red blood cells are rigid in order to prevent damage to the cell An important feature of red blood cells is their flexibility. Flexibility allows them to fit inside capillaries that are more narrow than the diameter of the red blood cell. Cells in the kidney produce the hormone erythryopoietin (EPO). EPO stimulates stem cells in the bone marrow to increase production of red blood cells. Memory tool: Lance Armstrong used exogenous EPO because he wanted to increase his red blood cell count. Having a higher red blood cell count would increase the amount of oxygen he could carry, allowing his muscles to have increased cellular respiration. Plasma is the noncellular, liquid component of the blood. The remainder of carbon dioxide travels in the blood in the form of bicarbonate ion (HCO3–). Red blood cells are packed with an enzyme known as carbonic anhydrase. Carbonic anhydrase combines CO2 with H2O into carbonic acid H2CO3 which dissociates into bicarbonate HCO3– and protons H+:

Answer 83

HCO3– is able to diffuse out of the cell, but H+ cannot. HCO3– is negatively charged and as HCO3– diffuses out of the cell, the cell loses a negative charge, and becomes more positive (due to H+). Negatively charged chloride ions Cl– must diffuse into the cell to replace the lost negative bicarbonate. This is known as the chloride shift.

Answer 84

D. Feeling cold Hypothyroidism would result in lowered metabolic rate, and less metabolic heat production, making the hypothyroid patient feel cold. Fast heartbeat, sweating, weight loss, and stunted growth would all be caused by inefficient, high levels of metabolism. Thyroid hormone stimulates a cell’s metabolic rate (the amount of energy it is producing from the nutrients it has). If a person does not produce enough thyroid hormone, they will have a low metabolic rate, and their body will ‘slow’ down. A side product of metabolism (and energy creation) is heat. When metabolic rate goes down, heat production in the body also goes down. As such, hypothyroid patients often feel cold.