BIO/BIOCHEM
A commonly used approximation of mean arterial pressure (MAP) relates to MAP to the measured systolic blood pressure (SBP) and diastolic blood pressure (DBP): MAP = 2/3DBP + 1/3 SBP. If the MAP increased by 10 mm Hg without a change in DBP, the new SBP would be: A. the original SBP plus 10 B. the original SBP plus 30 C. the original SBP plus 60 D. the original SBP plus 90
10 mm Hg = 1/3 delta SBP 3 x 10 mm Hg = 1/3 delta SBP x 3 30 mm Hg = delta SBP
Consider a region of the inner leaflet of a cell membrane in which phospholipid components help bind positively charged cytosolic molecules. What can be predicted about the identity and protonation state of the phospholipid components that most likely contribute to the binding? A. Binding must occur between the molecule and phospholipid heads with more deprotonated than protonated functional groups. B. Binding must occur between the molecule and phospholipid heads in which all functional groups are fully protonated C. Binding could occur between the molecule and phospholipid tails or heads that have more deprotonated than protonated functional groups. D. Binding could occur between the molecule and phospholipid tails or heads that have more protonated than deprotonated functional groups
A. Binding must occur between the molecule and phospholipid heads when more deprotonated than protonated functional groups. Protons contribute positive charges to molecules. Therefore, when more functional groups in a phospholipid head are deprotonated than protonated, the head group carries an overall negative charge and attracts positive molecules, facilitating binding.
Huntington's disease is a genetic neurodegenerative disorder that causes brain neurons to experience more action potentials than normal. It is know that activity of the neurotransmitter glutamate increases in these patients and activity of the neurotransmitter GABA decreases. Given this, these two neurotransmitters most likely have which of the following effects in the brain? A. Glutamate is an inhibitory neurotransmitter; GABA is an excitatory neurotransmitter B. Glutamate is an excitatory neurotransmitter; GABA is an inhibitory neurotransmitter C. Both glutamate and GABA are inhibitory neurotransmitters D. Both glutamate and GABA are excitatory neurotransmitters
A. Glutamate is an excitatory neurotransmitter; GABA is an inhibitory neurotransmitter
Which of the following is a citric acid cycle enzyme that produces a metabolite used directly in the electron transport chain? I. Malate dehydrogenase II. Glyceraldehyde 3-phosphate dehydrogenase III. Aconitase IV. Fumarase V. Isocitrate dehydrogenase A. I and V only B. II and V only C. III and IV only D. I, II, and V only
A. I and V only
An enzyme generates a Lineweaver-Burk plot with a slope of m. If the enzyme's Michaelis constant Km is known, which expression yields the maximum velocity Vmax of the enzyme-catalyzed reaction? A. Km/m B. Km x m C. m/Km D. Km + m
A. Km/m The slope of a Lineweaver-Burk plot if equal to Km/Vmax and the y-intercept is equal to 1/Vmax.
A certain multi-subunit protein consists of four regions, some of which contain cysteines that form disulfide bonds, as depicted in the diagram below. Treatment with a protease can cleave the protein into smaller fragments. Given this method, which regions of the protein shown below are NOT likely to be separated by protease treatment? A. Regions 1 and 2 B. Regions 1 and 3 C. Regions 2 and 3 D. Regions 3 and 4
A. Regions 1 and 2 Because proteases specifically target peptide bonds, a protease will not separate regions 1 and 2, which are only linked by a disulfide bond
Which statement best explains how osteocytes regulate compact bone remodeling? A. Signaling molecules released by osteocytes travel to other bone cells via canaliculi B. Osteocytes travel between lacunae to communicate with other bone cells C. Osteocytes differentiate into cells capable of producing signaling molecules that regulate bone remodeling D. Haversian canals provide a pathway for osteocyte travel in the bloodstream
A. Signaling molecules released by osteocytes travel to other bone cells via canaliculi
In a follow-up study, researchers studied the effect of a phosphomimetic mutation in acetyl-CoA carboxylase (ACC) that mimicked the effect of phosphorylated ACC on Drosophila stem cells. How will this mutation most likely compare to the effects of miR-277? A. The ACC mutation opposes the effect of miR-277 on fatty acid oxidation B. The ACC mutation has a similar effect as miR-277 on fatty acid oxidation C. Fatty acid oxidation is unaffected, but the ACC mutation will deplete citric acid cycle substrates similar to miR-277 D. The ACC mutation produces fatty acid oxidation substrates that will accumulate if co-expressed with miR-277
A. The ACC mutation opposes the effect of miR-277 on fatty acid oxidation Phosphorylation of ACC can occur through the enzymes protein kinase A or AMP-activated protein kinase. In both cases, the kinases signal a need for lipid catabolism to produce ATP. Therefore, phosphorylation of ACC or the introduction of phosphomimetic ACC mutants will promote fatty acid oxidation, which opposes miR-277 mediated inhibition of fatty acid oxidation
The researchers hypothesized that the bacterial lectin recognizes the intact PGN of live bacteria better than soluble PGN fragments from dead bacteria in vivo. Which of the following findings would be most consistent with this hypothesis? A. The apparent affinity of the lectin for full-length saccharides is greater than for any single binding site within the saccharide B. Cooperative binding to soluble PGN fragments with single lectin binding sites increases the apparent affinity of the lectin for each site C. Binding the lectin to a soluble PGN saccharide with a single lectin binding site increases dissociation of the lectin from full-length PGN D. The binding affinity of the lectin for soluble or insoluble PGN is the same when the total number of lectin binding sites are the same.
A. The apparent affinity of the lectin for full-length saccharides is greater than for any single binding site within the saccharide Because the lectin recognizes peptidoglycan through binding, greater binding affinity would be consistent with better recognition. Therefore, finding that the lectin binds the full-length peptidoglycan with greater affinity than it binds to peptidoglycan fragments would be consistent with the researchers' hypothesis
Researchers isolated peptidoglycan from a eukaryotic cell. The best explanation for this would be that: A. the eukaryotic cell is a host to a bacterial species containing peptidoglycan B. Peptidoglycan is a component of some eukaryotic cell walls C. Membranes within the eukaryotic cell contain peptidoglycan as a structural element D. A virus with a protein coat containing peptidoglycan infected the eukaryotic cell
A. The eukaryotic cell is a host to a bacterial species containing peptidoglycan
Although both thyroid hormone and epinephrine are synthesized from tyrosine, epinephrine behaves as a peptide hormone whereas thyroid hormone behaves like a steroid hormone. Given this, binding to a transport protein while in the circulation would likely occur for which hormone(s)? A. Thyroid hormone only B. Epinephrine only C. Both epinephrine and thyroid hormone D. Neither epinephrine nor thyroid hormone
A. Thyroid hormone only Peptide hormones are water soluble and circulate largely in the free form (ie, unbound to proteins), whereas steroid hormones are lipophilic and are predominantly bound to proteins in the circulation. Because it is an amino-acid derived hormone that behaves like a steroid hormone, thyroid hormone circulates bound to a transport protein.
Why was a mild oxidizing agent added during the experiments? A. To stabilize folded proteins by formation of disulfide bonds B. To stimulate denatured proteins to fold after the formation of disulfide bonds C. To stabilize folded protein by breaking disulfide bonds D. To stimulate denatured proteins to fold after breaking disulfide bonds
A. To stabilize folded proteins by formation of disulfide bonds Disulfide bonds are formed by the oxidation of two nearby thiol (--SH) groups. Disulfide bonds form a covalent linkage that strongly stabilizes local protein structure.
According to the Henderson-Hasselbalch equation, the pH range over which the EPN motif would go from being approximately 99% protonated to approximately 1% protonated is equal to: A. glutamate's R-group pKa plus or minus 2 pH units B. proline's R-group pKa plus or minus 2 pH units C. asparagine's R group pKa plus or minus 2 pH units D. the average of glutamate's amino-group pKa and asparagine's carboxyl group pKa, plus or minus 2 pH units
A. glutamate's R-group pKa plus or minus 2 pH units pH = pKa(Glu) + log ([deprotonated Glu]/[protonated Glu]) Because the logarithm of 99 (corresponding to 1% protonation) is approximately 2 and the logarithm of 1/99 (corresponding to 99% protonation) is approximately -2, the correct range is glutamate's R-group pKa, plus or minus 2 pH units
Enzyme A catalyzes the conversion of Substrate S to product P. When enzyme A is phosphorylated, its kcat value changes from 10 s^-1 to 5 s^-1 and its Km value changes from 100 micrometer to 20 micrometer. If equal concentrations of each enzyme form are used then compared to the unphosphorylated enzyme A, the phosphorylated form: A. has a higher catalytic efficiency and yields a faster reaction when [S] < 20 micrometer B. has a higher turnover number and yields a faster reaction rate under saturating conditions C. has a lower affinity for S and yields a slower reaction rate at all [S] D. is allosterically inhibited and yields a lower reaction rate at all [S].
A. has a higher catalytic efficiency and yields a faster reaction rate when [S] < 20 micrometer The question indicates that enzyme A undergoes a decrease in both kcat and Km upon phosphorylation. However, Km decreases by a greater factor than kcat, so the kcat/Km ratio increases. Therefore, the phosphorylated form of the enzyme has a higher catalytic efficiency than the unphosphorylated form, and the phosphorylated form yields a faster reaction rate at low concentrations (eg, below 20 micrometer)
When body surface area is affected by a burn, capillaries leak fluid containing serum proteins such as albumin. A burn patient is treated with continuous intravenous infusions of albumin during the healing process. Compared to a burn patient control (no albumin infusions), the treated patient's capillary oncotic pressure will most likely be: A. increased B. decreased C. the same D. increased, but fluid leakage will also increase over time
A. increased If such a burn patient is treated with continuous intravenous infusions of albumin during the healing process, the capillary solute concentration will increase, which will ultimately increase the capillary oncotic pressure. This pressure will promote water movement into the capillaries via osmosis. Compared to a control patient who did not receive albumin infusions, the treated patient will likely display increased capillary oncotic pressure due to a higher albumin (ie, solute) concentration in the plasma
2,4-Dinitrophenol (2,4-DNP) is a chemical that has historically been used for weight loss due to its ability to inhibit ATP synthesis. 2,4-DNP is a proton ionophore, a molecule that inserts into membranes, allowing for protons to passively move from one side to the other. When measuring OCR, scientists may add an ionophore like 2,4-DNP as a control, expecting to see: A. increased oxygen consumption as a result of increased activity of the electron transport chain B. increased oxygen consumption as a result of decreased activity of the electron transport chain C. decreased oxygen consumption as a result of increased activity of the electron transport chain. D. decreased oxygen consumption as a result of decreased activity of the electron transport chain.
A. increased oxygen consumption as a result of increased activity of the electron transport chain In this question, 2,4-DNP provides an alternative path to dissipate the proton gradient in addition to ATP synthase. This weakens the proton-motive force and also removes a product of the electron-transport chain: pumped protons. Via Le Chatelier's principle, this causes a rightward shift to restore equilibrium. The result is increased pumping of protons to the intermembrane space (increased ETC activity) and increased consumption of the reactants, including oxygen (increased OCR) which is the final electron acceptor.
The peptide bonds maintaining the amino acid sequence were left intact, despite the presence of denaturants. This is because the hydrolysis of peptide bonds: A. is thermodynamically favorable but kinetically unfavorable. B. is kinetically favorable but thermodynamically unfavorable. C. requires water molecules, which were not supplied. D. requires energy input from GTP, which was not supplied.
A. is thermodynamically favorable but kinetically unfavorable Because peptide bond hydrolysis is favorable but does not occur without enzymes, it is thermodynamically favorable but kinetically unfavorable
ACTC is a gene coding for cardiac actin. Patients exhibiting a specific mutation in this gene, called the E99K mutation, demonstrate a form of cardiac hypertrophy (cell enlargement) thought to be caused by increased sensitivity of the contractile apparatus to calcium. Given this, patients with the E99K mutation most likely demonstrate increased binding of: A. myosin to actin B. actin to troponin C. calcium to tropomyosin D. ATP to calcium
A. myosin to actin In this question, ACTC is a gene encoding a protein comprising of cardiac actin filaments. Patients with a specific ACTC mutation (E99K) demonstrate a form of cardiac hypertrophy (cell enlargement) thought to be caused by increased sensitivity of the contractile apparatus to calcium. Because of this, a lower intracellular concentration of calcium will be able to bind troponin and cause the conformational change required for the binding of myosin to actin and the subsequent contraction cycle. Therefore, patients with this mutation likely demonstrate increased binding of myosin to actin.
One function of the bulbourethral glands is to: A. secrete a mucus that is thick and alkaline B. facilitate sperm maturation C. transfer mature sperm to the urethra D. produce the largest portion of seminal fluid
A. secrete a mucus that is thick and alkaline Bulbourethral (Cowper's) glands- Glands that secrete thick, alkaline mucus to lubricate the tip of the penis. The alkalinity of the mucus neutralizes acids in the urine to protect the sperm from the acidic environment of the urethra.
Although some water is lost through sweat glands at the skin surface, the skin is relatively impermeable to water loss due to the cells of the: A. stratum corneum B. stratum basale C. dermis D. hypodermis
A. stratum corneum The most superficial layer of the epidermis, the stratum corneum, is composed of many layers of keratinocytes that have been pushed up from the deepest layers and flattened in the process. These flattened keratinocytes create a barrier to invasion by external pathogens and help prevent water and salt loss through the skin surface. Therefore, the skin is relatively impermeable to water loss largely due to the cells of the stratum corneum.
The cysteine-MPBS reaction is a redox reaction involving the nucleophilic attack on MPBS by a deprotonated cysteine side chain. If the reaction were attempted at pH 7.0, approximately what percent of cysteine side chains would be in the deprotonated, anionic form? (Note: assume that the cysteine side chains all have pKa of 8.0) A. 0% B. 10% C. 50% D. 75%
B. 10% Henderson-Hasselbalch equation- 7.0 = 8.0 + log [A-]/[HA] -1.0 = log [A-]/[HA] [A-]/[HA] = 10^-1.0 [A-]/[HA] = 1/10 = 10%
Compared to the control solution, monomeric mutant a-synuclein proteins decreased the total number of living cells and the number of living cells expressing PGP9.5 (Figure 2) by factors of approximately: A. 1.6 and 4, respectively. B. 2 and 1.6, respectively. C. 2 and 3, respectively. D. 3 and 4, respectively.
B. 2 and 1.6, respectively. Number of living cells after control solution treatment/Number of living cells after monomeric mutant a-synanuclein treatment = 300/150 = 2 Number of living cells expressing PGP9.5 after control solution treatment/Number of living cells expressing PGP9.5 after monomeric mutant a-synuclein treatment = 200/125 = 1.6
Assuming that 2 kg of skeletal muscle are exposed to conditions that cause the cleavage of 100 mmol of glucose monomers per kilogram of muscle (some of which are phosphorylated by the cleavage event), and that 90% of these monomers are released from glycogen by glycogen phosphorylase, what is the total amount of unphosphorylated glucose released into the cytosol by this process? A. 10 mmol B. 20 mmol C. 90 mmol D. 180 mmol
B. 20 mmol Total release of glucosyl monomers = release per kilogram muscle x kilograms of muscle Total release of glucosyl monomers = 100 mmol glucosyl monomers/kg muscle x 2 kg muscle = 200 mmol glucosyl monomers Total glucose release = total glycosyl monomer release x 10% Total glucose release = 200 mmol glucosyl monomers released x 0.10 = 20 mmol
Centrifugation of blood with an anticoagulant agent separates the blood components into layers by density. The least dense layer is the plasma. The plasma layer is most likely to include which component? A. Platelets B. Albumin C. Hemoglobin D. Neutrophils
B. Albumin Because albumin cannot easily cross capillary pores due to its size, it is an important solute for maintaining capillary oncotic pressure. The oncotic pressure maintained by solutes such as albumin causes a pulling force for water entry into capillaries via osmosis. The pressure is balanced by the pushing force of blood against capillary walls (hydrostatic pressure) which helps keep fluid in the vasculature
Researchers hypothesize that the hormone adiponectin significantly increases the activity of sebaceous glands in humans. Which of the following observations in patients deficient in adiponectin would best support this hypothesis? A. Decreased production of bile by the liver B. Decreased production of oils by the skin C. Decreased production of mucus by the trachea D. Decreased production of acid by the stomach
B. Decreased production of oils by the skin Sebaceous glands secrete sebum, an oil containing (hydrophobic) substance that helps prevent water loss from the skin and hair. Sebum also contains certain substances that inhibit the survival of pathogens, contributing to innate immunity
Which of the following conclusions is best supported by the information given in the passage? A. Differentiated cells contain less total mRNA content than stem cells B. Division and differentiation of enteroblasts to enterocytes involves a shift from catabolic to anabolic lipid metabolism C. Stem cells preferentially utilize glycolysis over fatty acid oxidation for energy production. D. As cells differentiate, miRNA-277 inhibition of some target genes is opposed by increased histone acetylation of other target genes
B. Division and differentiation of enteroblasts to enterocytes involves a shift from catabolic to anabolic lipid metabolism The passage states that proliferating stem cells increase miRNA-277 production, leading to a decrease in fatty acid oxidation and therefore to a decrease in fatty acid catabolism. Because the fatty acids are not being broken down to release energy, this indicates that a shift toward anabolic lipid metabolism has occurred and fatty acids are most likely needed for material purposes like membrane biosynthesis
Based on the passage, the inclusion of which amino acid is most likely responsible for the changing localization (soluble lumenal to integral membrane) of APOL1 upon pH manipulation? A. Isoleucine B. Glutamate C. Histidine D. Lysine
B. Glutamate Glutamate is an acidic amino acid that changes protonation state at different pH levels. At neutral pH, the glutamate side chain is negatively charged, and therefore highly soluble. When the pH drops, glutamate becomes protonated, which neutralizes its charge and makes it less water-soluble under acidic conditions. Therefore, the inclusion of glutamate is most likely responsible for the changing localization of APOL1.
If the unique properties of each amino acid in the EPN motif are necessary for carbohydrate binding, which of the following amino acids would best substitute for the asparagine residue? A. Phenylalanine B. Glutamine C. Aspartate D. Lysine
B. Glutamine Among the 20 most common amino acids in proline, asparagine is one of the two with polar, amide-containing R groups. The other such amino acid is glutamine; therefore, glutamine would best replace asparagine in a similar motif
The glucagon-induced entry of glucose derived from liver glycogen into the bloodstream for transport to other tissues involves close interaction among which enzymes? A. Glycogen phosphorylase, debranching enzyme, glycogen synthase B. Glycogen phosphorylase, debranching enzyme, phosphoglucomutase, glucose-6-phosphatase C. Debranching enzyme, phosphoglucomutase, glycogen synthase D. Debranching enzyme, phosphoglucomutase, phosphofructokinase, glucose-6-phosphatase
B. Glycogen phosphorylase, debranching enzyme, phosphoglucomutase, glucose-6-phosphatase The questions asks for the enzymes that closely interact to allow entry of glucose derived from liver glycogen into the bloodstream for transport other tissues. For this to occur, glycogen debranching enzyme and phosphorylase must act together to release G1P, which is subsequently converted to G6P and glucose by the actions of phosphoglucomutase and glucose-6-phosphatase, respectively.
Glucose can be synthesized from several molecules present in the body. Which statement best explains how glucose can be generated from both proteins and triglycerides in cells? A. The gluconeogenic precursor pyruvate is synthesized from amino acids in proteins or from fatty acids in triglycerides B. Hydrolysis reactions release the gluconeogenic precursors glycerol (from triglycerides) and amino acids (from proteins) C. Acetyl-CoA, a gluconeogenic precursor, can be synthesized from both amino acids and fatty acids. D. Phosphogluconate and acetyl-CoA are precursors that can enter the gluconeogenic pathway
B. Hydrolysis reactions release the gluconeogenic precursors glycerol (from triglycerides) and amino acids (from proteins). During proteolysis, amino acids are released from proteins by hydrolysis reactions. Similarly, triglyceride breakdown by lipases releases the glycerol backbone through hydrolysis. Therefore, glucose can be synthesized from glycerol and amino acids, which are gluconeogenic precursors derived from triglycerides and proteins, respectively.
Based on the passage, the functional RNase A recovered after the removal of denaturants and subsequent treatment with oxidizing agent displays which levels of protein structure? I. Primary II. Secondary III. Tertiary IV. Quaternary A. III only B. I, II, and III only C. II, III, and IV only D. I, II, III, and IV
B. I, II, and III only Quaternary structure exists only for multimeric proteins. The passage states that RNase A is a monomeric protein. Therefore, functional RNase A enzymes do not consist of the multiple polypeptide chains required for quaternary structure.
Which of the following catabolic pathways directly produce both ATP (or GTP) and NADH? I. Fatty acid oxidation II. Glycolysis III. The Krebs Cycle IV. The electron transport chain A. I and II only B. II and III only C. I, II, and III only D. II, III, and IV only
B. II and III only
In addition to sweating, increased temperatures will trigger: I. contraction of arrector pili muscles II. vasodilation of surface capillaries III. contraction of surface capillary smooth muscle A. I only B. II only C. I and III only D. II and III only
B. II only The other main response to increased temperatures is vasodilation of surface capillaries to release heat from the body to the environment.
The bioinformatic study described in the passage relies on the level of protein structure stabilized by: I. electrostatic interactions II. hydrogen bonds III. hydrophobic interactions IV. peptide bonds A. II only B. IV only C. III and IV only D. I, II, III, and IV
B. IV only The passage states that bioinformatics methods based on the APOL1 primary sequence were used to predict transmembrane regions. The primary sequence refers to the protein's primary structure, which is stabilized by covalent bonds such as the peptide bonds between individual amino acids
Hemodialysis is a procedure that filters blood for a patient whose kidneys are unable to do so. This procedure removes relatively large amounts of solutes and water from the patient's bloodstream in a short period of time. If a patient is undergoing hemodialysis, in which net direction would fluid flow across capillary walls near the end of the procedure? A. Into the capillaries, because the procedure decreased capillary solute concentration B. Into the capillaries, because the procedure reduced capillary hydrostatic pressure C. Into the interstitial fluid, because interstitial fluid osmolarity is increased D. Into the interstitial fluid, because overall blood volume is reduced
B. Into the capillaries, because the procedure reduced capillary hydrostatic pressure As hemodialysis occurs and blood is filtered, the removal of solutes and fluid from the patient's body by the dialysis machine reduces blood volume, which would in turn decrease CHP. Therefore, the net direction of fluid flow near the end of the procedure is into the capillaries because of reduced capillary hydrostatic pressure
Certain organisms can use ATP hydrolysis to help maintain their body temperature in cold conditions. Given that cleaving chemical bonds is always endothermic, which of the following explains why ATP hydrolysis is an exothermic reaction? A. The activation energy of hydrolysis is low and provides the energy needed to cleave the phosphoester bond B. More energy is released by the new bonds that form then is consumed by the initial bonds that break during hydrolysis C. The adjacent negative charged in the phosphate groups allow bond cleavage to produce thermal energy instead of consuming it D. The number of product molecules is greater than the number of reactant molecules
B. More energy is released by the new bonds that form than is consumed by the initial bonds that break during hydrolysis
The fatty acid B-oxidation pathway involves all the following molecules EXCEPT: A. FADH2 B. NADPH C. acetoacetyl-CoA D. B-hydroxyacyl-CoA
B. NADPH NADPH is produced during the pentose phosphate pathway and is used during fatty acid biosynthesis but is not involved in B-oxidation
One strategy to sensitize cancers to a particular treatment is to co-administer a second drug that brings the metabolic profile of a resistant phenotype closer to that of a sensitive one. Based on the passage, inhibition of which of the following enzymes or enzyme complexes is most likely to sensitize an otherwise resistant cell line to venetoclax? A. a-Ketoglutarate dehydrogenase B. Succinate dehydrogenase C. Malate dehydrogenase D. Pyruvate dehydrogenase
B. Succinate dehydrogenase A reasonable strategy to increase sensitivity is to inhibit Complex I or II. Complex II of the ETC is a multifunctional enzyme that also functions in the TCA cycle, where it is known as succinate dehydrogenase. Complex II oxidizes succinate to fumarate, generating an FADH2. The high-energy electrons from FADH2, are then deposited into other carriers for further transport. Therefore, inhibition of succinate dehydrogenase (Complex II) will likely increase venetoclax sensitivity.
In another study of human skin, it was found that the average number of pilosebaceous units (PSUs) was approximately 0.30 units per square millimeter. Which of the following statements best describes the relative densities of sweat glands and PSUs in an area of skin? A. Sweat glands are one-third as dense as PSUs B. Sweat glands are three times as dense as PSUs C. Sweat glands are one-fourth as dense as PSUs D. Sweat glands are four times as dense as PSUs
B. Sweat glands are three times as dense as PSUs Relative densities of sweat glands and PSUs = 0.945 glands/mm2/0.3 PSUs/mm^2 = 3 sweat glands/1 PSU = 3
Which statement best explains the effects of Graves' disease? A. The autoantibody acts as a hormone, and positive feedback control occurs on the autoantibody B. The autoantibody acts as a hormone, and affected individuals experience overproduction of thyroid hormones C. TSH receptors are stimulated by thyroid hormones D. Affected individuals experience decreased thyroid hormone production
B. The autoantibody acts as a hormone, and affected individuals experience overproduction of thyroid hormones The question states that individuals with Graves' disease show an increase in metabolism, which is a function of thyroid hormones. Therefore, production of thyroid hormones must be increased in these individuals.
What were the purposes of the experiment with MPB without streptavidin and of the experiment with MPBS and detergent? A. They served as a positive and negative control, respectively. B. They served as a negative and positive control, respectively. C. Both served as positive controls. D. Both served as negative controls.
B. They served as a negative and positive control, respectively. MPB without streptavidin is only 530 Da, approximately 1% of the size of APOL1. It is not expected to cause a significant size change on a western blot, regardless of whether it reacts with APOL1; therefore, MPB without streptavidin serves as a negative control. Negative controls help rule out the possibility that the cysteine mutations themselves (or some other confounding variable) cause a size change (ie, false positive). Detergents disrupt the stability of the cell membrane and allow MPBS to cross through and react with both extracellular and intracellular cysteines. Consequently, a size change is always expected regardless of cellular localization; therefore, MPBS with detergent acts as a positive control. This positive control helps prevent false negatives by ensuring that intracellular cysteines are reactive, and that a negative result is only due to localization
Which of the following statements best explains the data shown in Figure 1? A. Reflex arc overstimulation in muscle fibers was significantly reduced following treatment of rats with 60 mg/kg MDL B. Treatment with 120 mg/kg MDL significantly reduced reflexive muscle twitches 2 hours after treatment C. Reflex arc activity differed significantly among all post-injection time points in rats treated with 60 mg/kg MDL D. Treatment with 120 mg/kg MDL was sufficient to permanently recover normal reflex arc activity in rats with SCl.
B. Treatment with 120 mg/kg MDL significantly reduced reflexive muscle twitches 2 hours after treatment Figure 1 shows that 2 hours after 120 mg/kg MDL treatment, muscle twitching in SCl rats was significantly reduced compared to twitching in SCl rats treated with the DMSO control (ie, the confidence interval error bars do not overlap). However, 7 hours after this MDL injection, muscle twitches increased again (ie, to numbers significantly higher than those in rats without SCl), indicating that 120 mg/kg MDL was not sufficient to permanently recover normal reflex arc activity.
Cell differentiation during embryonic development is hypothesized to be controlled by differences in gene expression due to external and internal factors. Which experimental observation best supports a mechanism of cell differentiation that is due to internal factors? A. A gradient of signaling molecules triggers a cascade, leading to new gene expression in embryonic cells B. Unequal distribution of transcription factors across embryonic cells leads to differential gene expression C. Cell-to-cell contact induces new gene expression in an adjacent cell D. Differences in oxygen levels repress expression of certain genes
B. Unequal distribution of transcription factors across embryonic cells leads to differential gene expression Internal factors do not depend on interactions of cells with each other or with the environment, and result from inherent differences among individual cells. External factors influencing cell differentiation involve interactions with neighboring cells and the environment surrounding the cell Asymmetric distribution of transcription factors to embryonic cells during cell division is a mechanism of cell differentiation due to an internal factor. Other examples of internal factors include epigenetic modifications such as DNA methylation or chromatin remodeling
Scrapie is a transmissible neurodegenerative disease in sheep and goats caused by prions. Given this, a diagnosis of scrapie can most likely be confirmed by: A. PCR B. Western blot C. DNA sequencing D. introduction of specific siRNAs
B. Western blot A diagnosis of scrapie can most likely be confirmed by a procedure that detects specific proteins in the brains of these animals. Western blot, a method used to detect the presence of specific proteins, is a suitable technique to confirm a diagnosis of scrapie
Compared to the response that occurs during absorption of dietary carbohydrates, the response of glycogen particles to glucagon released during postabsorptive conditions is likely to result in: A. an increased incorporation of phosphorylated glucose molecules into glycogen particles B. an increased rate of phosphorylated glucose release from glycogen particles C. a decreased rate of glucose release from the nonreducing ends of glycogen branches D. an increased rate of phosphorylated glucose release from the reducing ends of glycogen branches
B. an increased rate of phosphorylated glucose release from glycogen particles Under these conditions, liver glycogen is broken down in the process of glycogenolysis to provide glucose for use in other tissues. This process is stimulated by the pancreatic hormone glucagon, which binds a receptor to initiate a signaling pathway leading to phosphorylated glucose release
Patients with central diabetes insipidus (CDI) excrete large volumes of urine with low osmolarity. Given this, the nephrons of CDI patients most likely possess: A. loops of Henle that penetrate into the inner region of the medulla B. collecting ducts composed of epithelial cells deficient in functional aquaporins C. large numbers of Na+/K+-ATPases in the cells of the proximal tubules D. highly active urea transporters in the distal portions of the collecting ducts
B. collecting ducts composed of epithelial cells deficient in functional aquaporins Because collecting duct aquaporins reabsorb water into the body, their production of excess dilute urine is likely due to collecting ducts that are deficient in functional aquaporins. The other options would increase water reabsorption, decreasing (not increasing) urine volume.
A protein found in Salmonella bacteria can exist as either a dimer that binds DNA and represses transcription of the gene encoding the protein or as a monomer that does not bind DNA. At lower temperatures (28 degrees Celsius), the bacteria expressed the protein at lower levels than at higher temperatures (37 degrees Celsius). These findings are most likely evidence of: A. disruption of primary but not tertiary structure at 37 degrees Celsius B. disruption of quaternary but not primary structure at 37 degrees Celsius C. alteration of both secondary structure and quaternary structure at 37 degrees Celsius D. alteration of neither secondary nor tertiary structure at 37 degrees Celsius
B. disruption of quaternary but not primary structure at 37 degrees Celsius At lower temperatures, less protein was produced, indicating that transcription was repressed. Thus, lower temperatures most likely prevent dimerization and subsequent repression of transcription. At higher temperatures, dimerization does not occur and transcription increases. Therefore, the experimental results provide the strongest support for the statement that quaternary structure is influenced by temperature and is disrupted at 37 degrees Celsius
Vitamin B12 is absorbed by the region of the digestive system that immediately precedes the cecum. Given this, vitamin B12 absorption most likely takes place in the: A. duodenum B. ileum C. jejunum D. colon
B. ileum Immediately before chyme enters the cecum, it is found in the ileum (final segment) of the small intestine. Therefore, vitamin B12 absorption most likely occurs in the ileum
Insulin molecules are degraded after receptor binding and internalization into target cells. Compared to the fasting state (low glucose uptake by target cells), the insulin degradation rate in a nondiabetic individual shortly after consuming a glucose solution will most likely be: A. approximately the same B. increased C. decreased D. decreased, but higher than in a diabetic individual
B. increased In a nondiabetic individual, drinking a glucose solution increases insulin binding to receptors on target cell plasma membranes, followed by internalization and destruction of the insulin. Therefore, the insulin degradation rate in a nondiabetic individual shortly after consuming a glucose solution will be increased (not approximately the same or decreased) relative to the fasting state
If miR-277 reduces acyl-CoA dehydrogenase mRNA levels to 50% of control levels, which of the following results is most consistent with the expected qPCR result? (Note: Ct is the threshold cycle, the PCR cycle number at which mRNA levels have been amplified to a prespecified final level.) A. miR-277 causes Ct to decrease to half the Ct value of control. B. miR-277 causes Ct to increase by one cycle, relative to control. C. miR-277 causes Ct to increase by two cycles, relative to control. D. miR-277 causes Ct to decrease by an unpredictable amount.
B. miR-277 causes Ct to increase by one cycle, relative to control. The question states that miR-277 causes acyl-CoA dehydrogenase mRNA levels to drop to 50% of control levels. Once enough PCR cycles have passed for the control sample to reach the threshold fluoresence, the miR-277 levels will still be at 50% of the threshold. One more cycle is required to double the miR-277-treated sample's DNA levels to reach 100% of the threshold
Pelvic organ descent and prolapse is a pathology in which abdominopelvic organs move downward and put pressure on lower organs. Pelvic organ descent and prolapse would most likely cause the function of the rectum to be: A. enhanced, resulting in a decreased frequency of solid waste excretion B. reduced, resulting in an increased frequency of solid waste excretion C. enhanced, resulting in an increased quantity of water reabsorbed from the feces D. reduced, resulting in a decreased quantity of water reabsorbed from the feces
B. reduced, resulting in an increased frequency of solid waste excretion The rectum is primarily responsible for storage of feces until its excretion. If pressure is put on the rectum, the storage area will be reduced. Therefore, a patient with pelvic organ descent and prolapse will likely experienced reduced rectal function, resulting in an increased frequency of solid waste excretion
The graph above shows the free energy of the products of each step of glycolysis relative to the free energy of glucose under typical cellular conditions (free energy of glucose is set to zero). Based on the data shown, the total free energy change during the energy investment reactions of glycolysis in which two molecules of glyceraldehyde-3-phosphate are formed, is closest to which of the following? A. -245 kJ/mol B. -95 kJ/mol C. -57 kJ/mol D. -39 kJ/mol
C. -57 kJ/mol The questions asks for the cumulative free energy change during the energy investment reactions of glycolysis, in which glyceraldehyde-3-phosphate is formed (ie, the first five reactions). Correct reading of the graph indicates that the cumulative free energy change after the fifth reaction of glycolysis is about -57 kJ/mol
Which series shows the order in which a human embryo develops? A. Fertilization, blastulation, morula formation, gastrulation, neuralation B. Fertilization, morula formation, blastulation, neurulation, gastrulation C. Fertilization, morula formation, blastulation, gastrulation, neurulation D. Fertilization, neurulation, morula formation, blastulation, gastrulation
C. Fertilization, morula formation, blastulation, gastrulation, neurulation
Which series shows the order by which an antigenic sequence of amino acids is brought in contact with a T-cell receptor by a major histocompatibility complex (MHC)? A. Full-length protein --> MHC I --> MHC II --> T-cell receptor B. Full-length protein --> MHC II --> MHC I --> T-cell receptor C. Full-length protein --> free digested protein fragments --> MHC II --> T-cell receptor D. Full-length protein --> free digested protein fragments --> MHC I --> free digested protein fragments --> T-cell receptor
C. Full-length protein --> free digested protein fragments -> MHC II --> T-cell receptor
In addition to the phosphorylation events described in the passage, glycogen synthase can be reversibly regulayed by glucose-6-phosphate binding to carboxy-terminal arginine residues outside the active site. Given this fact, what type of interaction represents allosteric regulation. A. Phosphorylation, because phosphoryl groups bind covalently B. Phosphorylation, because phosphoryl group binding can be reversed by phosphatases C. Glucose-6-phosphate binding, because it is noncovalent D. Glucose-6-phosphate binding, because it occurs with basic arginine residues
C. Glucose 6-phosphate binding, because it is noncovalent Allosteric modulators bind their targets reversibly via noncovalent interactions at sites outside the active site (ie, allosteric sites), thereby initiating a change in the structure and function of the target protein. Because G6P is a modulator that binds glycogen synthase through reversible, noncovalent interactions outside the active site, it is an example of allosteric regulation of glycogen synthase activity.
Which of the following conclusions about protein folding is best supported by the information in the passage? A. Proteins are folded properly only when folded co-translationally B. The purified RNase A sample was contaminated with chaperones that assisted in protein refolding C. Higher levels of RNase A protein structure are encoded in the primary structure. D. All denatured proteins can spontaneously refold to a native conformation.
C. Higher levels of RNase A protein structure are encoded in the primary structure The passage states that RNase A was fully denatured until only the amino acid sequence (primary structure) remained intact. Nevertheless, RNase A was able to refold to a functional state (ie, regain higher levels of structure) without an external energy source. Based on this evidence, it can be concluded that the higher levels of RNase A structure are encoded by its primary structure due to the dependency of protein structure levels
A scientist examining action potentials in mature muscle cells identifies certain muscle cells that, upon receiving an action potential, can directly transfer ions to adjacent cells. These cells would most likely include: I. smooth muscle cells II. cardiac muscle cells III. skeletal muscle cells A. I only B. II only C. I and II only D. II and III only
C. I and II only Ions cannot permeate the lipid bilayer of cell membranes directly and therefore require openings (such as gap junctions) to pass between cells. Accordingly, these cells likely include both smooth and cardiac muscle cells, which are the only muscle cell types that possess gap junctions.
During sarcomere contraction, which of the following would shorten in length? A. A band only B. H band only C. I band and H band only D. A band, I band, and H band
C. I band and H band only During sarcomere contraction, the lengths of both the I band and H band shorten as the actin and myosin filaments slide along one another. However, the A band, which corresponds to the length of the myosin filaments in one sarcomere, does not change in length.
Which of the following procedures would mimic the actions of the parasympathetic division of the nervous system? I. Severing certain vagus nerve fibers to reduce the activity of cells involved in stomach acid secretion II. Stimulating certain sacral nerve fibers to cause normal urination patterns as a treatment for loss of bladder control III. Stimulating certain facial nerve fibers supplying the submandibular glands to improve saliva production A. II only B. III only C. II and III only D. I, II, and III
C. II and III only One function of the parasympathetic division is maintaining normal urination patterns when an immediate stressor is not present, while the sympathetic division suppresses urination during stressful situations. The parasympathetic division is also responsible for increasing saliva production, which increases digestive activity, while the sympathetic division suppresses digestion.
Which type(s) of DNA are contained in a plasmid that can be used to transform bacteria in an experiment? DNA that is: I. single-stranded II. linear III. circular A. I only B. II only C. III only D. I and II only
C. III only The question asks for the type of DNA contained in a plasmid used to transform bacteria in an experiment. In both experimental and naturally occurring settings, plasmid DNA is circular, double-stranded, and not part of a chromosome.
Which of the following situations would NOT cause vasoconstriction to occur? A. Loss of blood B. Exposure to cold temperatures C. Increased blood pressure D. Secretion of renin
C. Increased blood pressure In this case, vasocontriction would cause the blood pressure to increase to an even greater extent, taking the individual further from homeostasis. Therefore, an increase in blood pressure would lead to vasodilation, which decreases blood pressure to homeostasis levels
Sustained excess nutrient intake can result in resistance of target cells to insulin. Compared to normal patterns after a meal, which of the following best describes an effect of insulin resistance? A. Liver cells form glycogen at a higher rate B. Liver cells secrete glucagon at a lower rate C. Liver cells produce glucose at a higher rate D. Kidney cells secrete glucose at a lower rate
C. Liver cells produce glucose at a higher rate Liver cells are targeted by insulin to decrease glucose production and increase glycogen formation after a meal. However, if these target cells are resistant to insulin, glucose production will likely occur at a lower rate than normal. Therefore, compared to normal patterns after a meal, insulin resistance is likely to result in higher rates of glucose production by liver cells.
Which of the following conclusions regarding small intestine function in MT mice compared to WT mice is best supported by the information shown in Figure 1? A. MT mice increased their rate of muscle contraction to compensate for reduced movement of food through the small intestine tract B. MT mice exhibited decreased rates of sarcomere contractions in muscle surrounding the small intestine C. MT mice exhibited reduced coordination of nonstriated muscle contractions in the small intestine tract lining D. MT mice more rapidly accumulated waste from the small intestine in the colon
C. MT mice exhibited reduced coordination of nonstriated muscle contractions in the small intestine tract lining Because smooth (nonstriated) muscle contraction (ie, peristalsis) controls the movement of food through the small intestine portions of the GI tract, these data indicate that, compared to WT mice, MT mice likely exhibited reduced coordination of nonstriated muscle contractions in the small intestine tract lining.
Do the results presented in Table 1 support the hypothesis that the osmoregulatory function of the skin is impaired in aged individuals? A. Yes; the average secretory duct length was significantly shorter in the aged group compared to the young group. B. Yes; the average sweat gland density was significantly lower in the aged group compared to the young group. C. No; average sweat gland volume did not differ significantly between the two experimental groups, suggesting that similar amounts of water and solutes are released by individuals in the two groups D. No; average secretory duct depth did not differ significantly between the two experimental groups, suggesting that osmoregulation by the skin is not impacted by age
C. No; average sweat gland volume did not differ significantly between the two experimental groups, suggesting that similar amounts of water and solutes are released by individuals in the two groups
The researchers hypothesized that glycogenin is required for normal glycogenesis in all body tissues. Do the results produced in Figure 1 support this hypothesis? A. Yes; glycogen concentrations were normal or above normal in both liver and heart when glycogenin was present B. Yes; glycogen concentrations were abnormally high in hearts of heterozygous mice with reduced glycogenin expression C. No; glycogen concentrations were normal in the livers of all mice D. No; glycogen concentrations were correlated with glycogenin gene expression in both liver and heart
C. No; glycogen concentrations were normal in the livers of all mice If glycogenin is required for normal glycogenesis in all body tissues, mice lacking glycogenin should have abnormal tissue glycogen concentrations. Although heart glycogen concentrations were abnormal in heart tissue from both the GN(+/-) and GN(-/-) mice, consistent with the researcher's hypothesis, liver glycogen concentrations were normal in liver tissue of mice lacking glycogenin. Therefore, the hypothesis that glycogenin is required for normal glycogenesis in all body tissues is not supported by the results.
If glucose-6-phosphate is used for NADPH synthesis more than for NADH synthesis inside a cell, which of the following metabolic processes is most active in the cell? A. Reduction of glucose metabolites in the cytosol to produce ATP B. Reduction of antioxidant NADP+ molecules C. Production of five-carbon sugar phosphates in the cytosol D. Oxidation of glucose metabolites inside mitochondria to produce CO2
C. Production of five-carbon sugar phosphates in the cytosol Greater use of glucose-6-phosphate for NADPH synthesis than for NADH synthesis indicates that production of pentose sugar phosphates is the most active metabolic process among those listed
Which of the following correctly describes what happens when DNA polymerase adds a deoxyribonucleotide triphosphate (dNTP) to a growing DNA strand? A. The hydroxyl group at the 5' end of the growing strand attacks the 3' a-phosphate of the dNTP B. The phosphate group at the 5' end of the growing strand attacks the 3' hydroxyl group of the dNTP C. The hydroxyl group at the 3' end of the growing strand attacks the 5' a-phosphate of the dNTP D. The phosphate group at the 3' end of the growing strand attacks the 5' hydroxyl group of the dNTP
C. The hydroxyl group at the 3' end of the growing strand attacks the 5' a-phosphate of the dNTP
The cleavage of fructose 1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroacetone phosphate is thermodynamically unfavorable, with a delta G of +23.8 kJ/mol. However, in most cells the reaction readily proceeds to the right. Which of the following best explains this observation? A. This reaction is coupled to the hydrolysis of ATP in vivo. B. This is a multistep reaction with an exergonic elementary step C. The products quickly participate in other reactions D. The enzyme that catalyzes this reaction lowers the activation energy to shift equilibrium
C. The products quickly participate in other reactions Changing concentrations of products or reactants can shift reactions in the forward or reverse direction and the delta G value will change to reflect the new equilibrium
Malonyl-CoA is an intermediate in fatty acid synthesis and an inhibitor of long-chain fatty acid transport to the mitochondria. Given this information, which of the following experimental results would provide evidence that a certain drug causes cells to carry out increased beta oxidation? A. Adding malonyl-CoA to drug-treated cells causes an increase in the level of cytosolic acetyl-CoA compared to cells without malonyl-CoA treatment B. Adding malonyl-CoA to drug-treated cells causes a decrease in the level of mitochondrial acetyl-CoA compared to cells without malonyl-CoA treatment C. Treating cells with the drug results in a decreased concentration of cytosolic malonyl-CoA compared to untreated cells D. Treating cells with the drug results in an increased concentration of cytosolic malonyl-CoA compared to untreated cells
C. Treating cells with the drug results in a decreased concentration of cytosolic malonyl-CoA compared to untreated cells If treatment with a drug led to lower levels of cytosolic malonyl-CoA, beta oxidation could increase as more fatty acids enter the mitochondria. Therefore, the observation that treatment with a drug results in a decreased concentration of cytosolic malonyl-CoA would be one piece of evidence to suggest that the drug causes increased beta oxidation
In a different experiment, the scientists found that transferring contents from the colons of WT mice into the colons of MT mice decreased the severity of PD symptoms that developed in MT mice over time. The best explanation for this observation is that: A. healthy bacterial species from WT mice transferred to the colons of MT mice could express large amounts of wild-type a-synuclein protein and restore ENS and CNS function B. many antimicrobial compounds in the GI tracts of WT mice significantly decreased GI bacteria numbers in MT mice, enhancing neuron function. C. WT mice contained specific amounts and types of GI bacterial species that could colonize the intestines of MT mice and improve ENS and CNS function D. the GI tracts of WT mice contained only mostly bacterial species with genetic similarities, increasing bacterial genetic diversity and neuron function in MT mice.
C. WT mice contained specific amounts and types of GI bacterial species that could colonize the intestines of MT mice and improve ENS and CNS function Because the colon contents of WT mice could contain a portion of their gastrointestinal (GI) bacterial species, this procedure most likely supplied MT mice with gut flora from healthy WT mice. Therefore, the best explanation for decreased severity of Parkinson's symptoms in MT mice is that WT mice contained specific amounts and types of GI bacteria that could colonize the intestines of MT mice and improve ENS and CNS function
In a certain bacterial lectins that are similar to the one that was tested, carbohydrate binding is mediated by an X-P-X motif, in which X refers to amino acids that replace E and N in the EPN motif. The best explanation for proline's presence in both motifs is that: A. proline's side chain charge facilitates ionic interactions with carbohydrates B. proline's side chain provides flexibility in the positioning of its neighboring amino acids C. a secondary amino group is required for favorable positioning of the neighboring amino acids D. aliphatic amino acids with larger side chains are more hydrophobic, which prevents carbohydrate binding
C. a secondary amino group is required for favorable positioning of the neighboring amino acids Proline is unique among the 20 amino acids commonly found in proteins in that it is the only one that possesses a secondary amino (imino) group. Therefore, the best explanation for proline's presence in both motifs is that a secondary amino acid is necessary for optimal positioning of its neighboring amino acids.
Cells of the innate immune system and cells of the adaptive immune system differ in that only the latter: A. mount an immediate response against pathogens B. are produced by bone marrow stem cells. C. bind only one type of antigen D. express antigen-presenting proteins on their cell surface.
C. bind only one type of antigen Cells of the innate immune system rapidly and nonspecifically mount immune responses against foreign antigens. Innate immune cells can respond to many types of foreign antigens and cellular stress signals to mount immediate responses against invading pathogens. In contrast, cells of the adaptive immune system recognize and bind only one type of foreign antigen, mounting specialized immune responses against invading pathogens.
Based on the passage, miR-277 most likely also targets: A. pyruvate dehydrogenase B. acetyl-CoA carboxylase C. carnitine palmitoyltransferase I D. B-ketoacyl-ACP synthase
C. carnitine palmitoyltransferase I The passage states that miR-277 targets fatty acid oxidation enzymes, including acyl-CoA dehydrogenase and acetyl-CoA acyltransferase. CPTI, the enzyme that brings the fatty acid across the outer mitochondrial membrane, is considered the rate-limiting enzyme of fatty acid oxidation. Therefore, miR-277, which targets mRNA of enzymes of fatty acid oxidation, likely targets CPTI as well
When present in exocrine gland cells, specific chloride channels reabsorb chloride ions from fluids in the exocrine gland lumen. Individuals with cystic fibrosis, an inherited disorder involving mucus buildup in certain tissues, exhibit decreased function of these chloride channels. An individual with cystic fibrosis in a hot environment is likely to demonstrate: A. high plasma chloride ion levels B. low osmolarity of fluid in sweat gland lumens C. high chloride ion concentrations in secreted sweat D. low numbers of chloride channels in exocrine glands
C. high chloride ion concentrations in secreted sweat This individual's sweat will contain a high concentration of chloride ions because few chloride ions will be reabsorbed by the dysfunctional chloride channels in sweat gland cells. Therefore, in a hot environment, an individual with cystic fibrosis will demonstrate high chloride ion concentrations in secreted sweat
The amount of antibiotic given to a patient with elevated kidney function who has a bacterial infection, compared to the amount given to patient with normal kidney function, should be: A. the same B. decreased C. increased D. increased, but the antibiotic will have a greater effect
C. increased Due to increased CrCl in a patient with elevated kidney function, substances are cleared from the kidney at a faster rate than they are in a healthy (ie, normal kidney function) patient. Therefore, compared to a healthy patient, a patient with elevated kidney function requires an increased (not decreased) amount of antibiotic for it to have the same effect
The skeletal muscles collectively contain more than twice as much glucose stored in glycogen as is found in the liver. Compared with the liver, the amount of glucose released into the blood from muscles is likely: A. greater from glycogenolysis, but less from gluconeogenesis B. the same from glycogenolysis, but more from gluconeogenesis C. less from both glycogenolysis and gluconeogenesis D. the same from both glycogenolysis and gluconeogenesis
C. less from both glycogenolysis and gluconeogenesis Because skeletal muscle lacks significant levels of glucose-6-phosphatase, it is poorly equipped to convert glucose-6-phosphate (G6P) derived from glycogenolysis or gluconeogenesis into glucose for release into the blood. Although a small proportion of the glucose residues released during skeletal muscle glycogenolysis are free (ie, unphosphorylated) glucose, these glucose molecules will likely be trapped inside the cell as G6P due to the activity of hexokinase. Therefore, glucose release into the blood from muscle glycogenolysis and gluconeogenesis (if any occurs) is much less than from the two processes in the liver.
A method for increasing the quantity of aquaporins in the collecting duct cells of the kidney during a certain period would be: A. increasing extracellular sodium ion concentrations B. stimulating aldosterone production C. stimulating antidiuretic hormone production D. increasing blood pressure
C. stimulating antidiuretic hormone production. The hormone responsible for activating a pathway that leads to the insertion of more aquaporins in collecting duct cells is antidiuretic hormone (ADH) or vasopressin. By stimulating ADH production, aquaporin insertion would increase in collecting duct cells, causing an increase in water retained by the body
What is the cardiac output of an individual whose tissues take up 350 mL of O2 per minute and whose arterial-venous difference is 5 mL O2 per 100 mL of blood? A. 0.7 mL/min B. 7 mL/min C. 70 mL/min D. 7000 mL/min
Cardiac output = 70 x 100 mL blood/min = 7,000 mL blood/min
Based on Figure 1, if a single epinephrine molecule binding to its receptor results in 10 active PKA molecules, 20 cAMP molecules, and 100 active glycogen phosphorylase b kinase molecules being produced, the signal amplification induced by PKA phosphorylating its target would be: A. 1/5 B. 1/2 C. 2 D. 10
D. 10 SA = Mafter/Mbefore SA = 100 molecules (of active glycogen phosphorylase b kinase)/10 molecules (of active PKA) = 10 fold amplification
The Michaelis-Menten kinetic parameters were measured for enzyme E with substrate S, yielding a Km value of 2.5 mM and a Vmax of 100 nM/min. If this first experiment were to be repeated with triple the concentration of enzyme, what would be the initial reaction velocity (V0) for this second trial when [S] = 7.50 mM? A. 75 nM/min B. 100 nM/min C. 150 nM/min D. 225 nM/min
D. 225 nM/min V0 = Vmax ( [S]/Km + [S]) = 300 nM/min (7.5/2.5 mM + 7.5 mM)
Which of the following experiments would best test this prediction? A. Fluorescently label the proposed glycosyltransferase, mix it with the substrate protein and donor molecule, then assess whether the proposed glycosyltransferase is retained on a column that binds the carbohydrate B. Mix the substrate protein and donor molecule, with or without the proposed glycosultransferase, then perform a Western blot using an antibody specific to the substrate protein. C. Incubate the donor molecule and substrate protein, with or without the proposed glycosyltransferase, then use mass spectrometry to measure the mass of the donor molecule D. Add a tritium label to the carbohydrate, incubate the donor molecule and substrate protein with or without the proposed glycosyltransferase, then measure tritium levels in the purified substrate protein
D. Add a tritium label to the carbohydrate, incubate the donor molecule and substrate protein with or without the proposed glycosyltransferase, then measure tritium levels in the purified substrate protein To conclude that a given enzyme is a transferase, the chemical group of interest must be observed moving from one molecule to another in the presence, but not the absence, of the enzyme.
Which statement most likely explains the reduction in protein secretion observed in the motor neurons of individuals with PD? A. Aggregated a-synuclein proteins promote higher expression of cytoskeletal proteins in the axons of motor neurons B. Aggregated a-synuclein proteins increase the production of molecules that negatively regulate smooth endoplasmic reticulum function C. Aggregated a-synuclein proteins reduce expression of plasma membrane proteins required for the facilitated diffusion of molecules from motor neurons D. Aggregated a-synuclein proteins impair intracellular vesicle transport between the rough endoplasmic reticulum and the Golgi apparatus in motor neurons
D. Aggregated a-synuclein proteins impair intracellular vesicle transport between the rough endoplasmic reticulum and the Golgi apparatus in motor neurons Because proteins secreted from cells are synthesized in the RER and transported to the Golgi apparatus for packaging, the most likely explanation for this reduced protein secretion is that aggregated a-synuclein proteins impair intracellular vesicle transport between the RER and Golgi apparatus in motor neurons
Which series shows the order in which blood passes through the pulmonary circulation? A. Vein --> Venule --> Capillary --> Arteriole --> Artery B. Venule --> Vein --> Capillary --> Artery --> Arteriole C. Arteriole --> artery --> Capillary --> vein --> venule D. Artery --> arteriole --> capillary --> venule --> vein
D. Artery --> arteriole --> capillary --> venule --> vein
Central retinal vein occlusion (CRVO), a disorder that leads to blindness, is thought to be caused by erythrocytes attaching to the interior lining of the central retinal vein. Erthyrocytes most likely adhere to which structures in patients with CRVO? A. Smooth muscle cells B. Platelets C. Leukocytes D. Endothelial cells
D. Endothelial cells The interiors of all cardiovascular components (heart, blood vessels) are lined with endothelial cells. Therefore, in a patient with CRVO, erythrocytes most likely adhere to the endothelial cells lining the central retinal vein, causing vein occlusion that leads to blindness
A peptide hormone secreted by small intestine endocrine cells and enteric neurons in WT mice was found to increase the release of digestive enzymes and stored bile into the small intestine lumen but did not increase the secretion of digestive enzymes into the stomach. Given this information, which of the following is NOT likely an effect of this hormone on digestive processes? A. Activation of receptors on exocrine cells of the pancreas B. Stimulation of gallbladder contraction C. Increased production of lipid micelles in the small intestine D. Enhanced release of pepsinogen from chief cells
D. Enhanced release of pepsinogen from chief cells Chief cells release the digestive enzyme pepsinogen into the stomach, where its active form (ie, pepsin) aids in protein digestion. However, the question states that the peptide hormone did not increase (ie, enhance) the secretion of digestive enzymes into the stomach. Therefore, enhanced release of pepsinogen from chief cells is not likely effect of this hormone on digestive processes
The release of sweat is partially under the control of which hormone? A. Somatostatin B. Antidiuretic hormone C. Parathyroid hormone D. Epinephrine
D. Epinephrine Epinephrine is a hormone released by the adrenal medulla in response to a stressor. Epinephrine release leads to redirection of blood flow in the body via vasoconstriction and vasodilation, increased heart rate, dilation of bronchioles, and sweat release. These are hallmarks of the "fight-or-flight" response of the sympathetic nervous system. Therefore, the release of sweat is partially under the control of epinephrine.
In the years before having her thyroid gland removed, a temporary decrease in Melissa's circulating thyroid hormone concentrations would have caused a compensatory response. Within the endocrine axis that includes thyroid hormone, which tissue(s) would respond to a temporary reduction in thyroid hormone concentration? A. Hypothalamus only B. Adrenal only C. Pituitary only D. Hypothalamus and pituitary
D. Hypothalamus and pituitary Thyroid hormone production is regulated through the linked activities of the hypothalamus, pituitary, and thyroid gland (ie, the hypothalamic-pituitary-thyroid [HPT] axis).
The consumption of excessive amounts of alcohol can lead to very high levels of acidity in the blood. Which of the following pairs of renal responses would most likely take place following excessive alcohol consumption? I. secretion of H+ II. secretion of HCO3- III. reabsorption of H+ IV. reabsorption of HCO3- A. I and II only B. II and III only C. III and IV only D. I and IV only
D. I and IV only To lower acidity, more H+ ions should be removed from the blood. Accordingly, nephrons would likely respond by secreting H+ in the proximal and distal tubules and the collecting duct to increase blood pH, allowing H+ ions to enter the urine. Additionally, HCO3- ions would be reabsorbed in the proximal and distal tubules and in the collecting duct and transferred back into the bloodstream. This would lead to the accumulation of HCO3- in the blood, which acts as a buffer, binding H+
Which of the following pairs of enzymes are involved in the release of individual monomers from glycogen? I. Phosphoglucomutase II. Glucose-6-phosphatase III. Glycogen phosphorylase IV. Debranching enzyme A. I and II only B. I and III only C. II and IV only D. III and IV only
D. III and IV only Phosphorylase acts upon linear glycogen regions, catalyzing the release of glucose residues from the nonreducing end (ie, the end with a glucose molecule that only participates in one glycosidic bond). Debranching enzyme "linearizes" branched regions of glycogen, repositioning them onto the ends of short linear segments and releasing one glucose residue from the branch in the process
Administration of which hormone is most likely to replicate the effects of miR-277 on fatty acid oxidation in mammalian cells? A. Cortisol B. Epinephrine C. Glucagon D. Insulin
D. Insulin High blood glucose levels generally indicate plentiful food availability; therefore, insulin inhibits fatty acid oxidation and stimulates fatty acid synthesis to store metabolic fuel during periods of food abundance. Because miR-277 acts to inhibit fatty acid oxidation, a hormone that also inhibits fatty acid oxidation is needed to replicate miR-277 activity. Of the options given, insulin is most likely to perform this function.
Where in the cell are short and medium chain fatty acids activated and oxidized? A. Cytosol B. Nucleus C. Smooth endoplasmic reticulum D. Mitochondria
D. Mitochondria Fatty acid oxidation and activation to acyl-coenzyme A molecules are carried out by mitochondria
Assume that a patient who was originally infected with a certain strain of bacteria becomes reinfected with the same strain. Of the following cell types, which is LEAST likely to produce memory cells during the initial infection that would rapidly respond to the new infection? A. B cell B. Cytotoxic T cell C. Helper T cell D. Neutrophil
D. Neutrophil Of the various immune cell types, neutrophils are the most numerous. They are innate (ie, nonspecific) immune cells that perform various functions, including the killing of pathogens via phagocytosis and the release of granules (ie, particles) that contain compounds (ie, antimicrobials) toxic to invading pathogens. Neutrophils also destroy pathogens by releasing DNA-containing material called neutrophil extracellular traps, and they release cytokines (chemical signals) that help regulate immune responses. However, unlike B and T cells of the adaptive immune system, innate neutrophils do not produce memory cells.
Which of the following enzyme-catalyzed reactions does NOT involve an oxidoreductase? A. Glucose-6-phosphate + NADP+ --> 6-phosphogluconolactone + NADPH + H+ B. Cystine + NADH + H+ --> 2 cysteine + NAD+ C. 4 Cytochrome Cred + O2 + 4H+ --> 4 Cytochrome Cox + 2 H2O D. Nicotinamide mononucleotide + ATP --> NAD+ + pyrophosphate
D. Nicotinamide mononucleotide + ATP --> NAD+ + pyrophosphate Although this reaction involved NAD+, it does not involve conversion of NAD+ to NADH or vice versa; thus, it is not a redox reaction. Instead, it is a transfer reaction in which an adenosine monophosphate (AMP) group is transferred from ATP to NMN, leaving pyrophosphate (PPi). Therefore, this reaction is catalyzed by a transferase, not an oxidoreductase
During glycogen breakdown, if the average rate that each residue stored in liver glycogen particles is released as phosphorylated glucose is directly proportional to the particle's surface area to volume ratio, which of the following statements describes the expected relative rates of glucose 1-phosphate release from individual liver glycogen a and B particles? A. Release from a particles is 100 times faster than that from B particles B. Release from a particles is 10 times faster than that from B particles C. Release from a particles is the same rate as that from B particles D. Release from a particles is one tenth as fast as that from B particles
D. Release from a particles is one tenth as fast as that from B particles
The GPR143 gene is located on the X chromosome and mutations in this gene can cause ocular albinism (OA), a recessive condition in which pigmentation in the eye is affected. A couple has three children: two of them (a girl and a boy) have OA but a third child (a girl) is not affected. Which of the following conclusions about the inheritance of OA in this family can be drawn? A. The OA allele is carried by both parents B. The disorder will likely be passed to 100% of their sons C. The disorder will likely be passed to 25% of their daughters D. The father has OA
D. The father has OA The question asks what conclusions can be drawn about this disorder's inheritance, given that it is X-linked recessive, and the couple has both a son and daughter with OA and a daughter without OA. For this situation to occur, father must have OA and the mother must be a carrier. Even though the father possesses only one Xa allele, he will have the condition because he does not have a second X chromosome
The Km of an enzyme is always decreased by which class of inhibitor? A. Mixed B. Noncompetitive C. Competitive D. Uncompetitive
D. Uncompetitive Because uncompetitive inhibitors bind ES exclusively, they always cause a decrease in Km.
Researchers have found that the nucleotide composition of structural RNAs (eg, tRNA, rRNA, other RNAs that show intra- and inter-strand hybridization) differs between thermophiles, which thrive at elevated temperatures, and mesophiles, which thrive at moderate temperatures. Compared with the structural RNA of mesophiles, the structural RNA of thermophiles most likely contains a higher proportion of: A. adenine and guanine nucleotides B. adenine and uracil nucleotides C. cytosine and uracil nucleotides D. guanine and cytosine nucleotides
D. guanine and cytosine nucleotides For these structural RNAs, the stability of the RNA double helix is critical. A larger percentage of G=C base-pairs, which involve more hydrogen bonds than either A=T or A=U base pairs, is associated with a larger, more stable Tm; therefore, thermophile structural RNA sequences are more likely to have a higher proportion of guanine and cytosine nucleotide residues to make the RNA duplexes more heat-stable
Clonal selection of B or T cells would require: A. a population of B cells, all of which express identical antigen receptors B. a population of T cells producing a variety of antibodies, which are released into circulation C. immune cells presenting antigens specific for a particular B cell's antigen receptor D. immune cells presenting antigens specific for a particular T cell's antigen receptor
D. immune cells presenting antigens specific for a particular T cell's antigen receptor Clonal selection requires- - A variety of B and T cell clones - Antigen receptors for a specific pathogen - Replication of antigen-responsive clones
A neurotransmitter identified in the spinal cord of rats normally function to bind ligand-gated Cl- channels on motor neurons, facilitating the diffusion of Cl- into the neurons and altering neuron membrane potential. Given this information, rats with downregulated KCC2 function in motor neurons due to SCl would most likely exhibit: A. abnormally rapid active transport of Cl- out of motor neurons upon binding the neurotransmitter B. abnormally rapid diffusion of Cl- into these motor neurons following neurotransmitter release C. reduced ability of the neurotransmitter to promote depolarization of cell membranes in these motor neurons D. reduced ability of the neurotransmitter to promote hyperpolarization of cell membranes in these motor neurons.
D. reduced ability of the neurotransmitter to promote hyperpolarization of cell membranes in these motor neurons. In rats with SCl, reduced KCC2 activity would cause motor neurons to exhibit Cl- concentrations higher inside the cell and lower outside the cell than in wild-type rats due to decreased active transport of Cl- to the extracellular environment. This change would serve to decrease the concentration gradient for Cl-, causing decreased (not abnormally rapid) diffusion of Cl- into motor neurons via ion channels bound by this neurotransmitter
Channel X in trypanosomes was also found to be activated upon pH neutralization of cells treated with APOL 1. This response to pH is lost in the absence of APOL1 treatment. In cells transfected with the nicotinic acetylcholine receptor (nAChR), Channel X remains inactive upon pH modulation but can instead be activated following treatment with acetylcholine. Channel X is best described as a: A. mechanically gated ion channel B. pH-activated channel C. ligand-gated ion channel D. voltage-gated ion channel
D. voltage-gated ion channel Voltage-gated ion channels respond to changes in the membrane potential that have usually been caused by other channels. By responding to other ion channels, voltage-gated channels can propagate an electrical stimulus across the surface of a cell. Because Channel X only activates upon the activation of (and the subsequent resultant depolarization by) either APOL 1 or nAChR, Channel X is most likely a voltage-gated ion channel