Med Board Biochem MCQ-Answer Key

BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 1. Amino acids: A. have more than one a-carbon atom. B. cannot participate in covalent bond formation. C. only ever have two pKs. D. are all chiral, except for glycine. E. occur in nature exclusively in the optically active D-form. 2. The pI of a protein is the: A. pK value of the functional groups attached to the a-carbon. B. pH value at which it has no charge. C. pH value at which the protein is generally most soluble. D. pH value at which its net charge is zero. E. net pK value of all the ionizable side chains and R-groups. 3. Select the TRUE statement. A. Secondary structure of a polypeptide is principally responsible for determining its molecular weight. B. Tertiary structure of a polypeptide is principally responsible for most of the alpha helical and beta-pleated sheet motifs it displays. C. Primary structure of a polypeptide results from methionines being oxidized to disulfide bonds. D. Polypeptide domain units are formed by phosphorylation of serines and threonines. E. The quaternary structure of a protein implies that more than one polypeptide chain composes that protein. 4. An enzyme in liver which is part of both the glycolytic and gluconeogenic pathways is: A. glucose 6-phosphatase. B. PEP carboxykinase. C. fructose 1,6-bisphosphatase. D. glucokinase. E. glyceraldehyde 3-phosphate dehydrogenase. 5. Fructose 2,6-bisphosphate: A. is required for gluconeogenesis. B. synthesis is stimulated by insulin. C. is increased by cyclic AMP. D. inhibits phosphofructokinase. E. stimulates fructose 1,6-bisphosphatase. 6. Which of the following statements regarding Michaelis-Menten kinetics is TRUE? A. The Km is the dissociation constant of the enzyme-substrate complex. B. The Km is the concentration of the substrate at Vmax. C. The Km is measured at high substrate concentration. D. The Km is the substrate concentration where half of the enzyme is in the form of enzymesubstrate complex. 7. Your patient is a 25 year old male who was admitted to the hospital in a state of starvation. He had been homeless for several months and become depressed and had not eaten for 4 days. You start him on a high carbohydrate diet as an attempt to spare protein and restore normal blood sugar regulation. Which of the following enzymes is most likely to increase in concentration in his liver? A. Glucose 6-phosphatase. B. Glucokinase. C. Pyruvate kinase.

D. Succinate dehydrogenase. E. Hexokinase.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 8. The standard free energy change for a metabolic pathway: A. is positive for spontaneous pathways. B. is inversely proportional to the rate of the overall pathway. C. is lower in the presence of the pathway enzymes. D. is the sum of all the individual standard free energy values. E. depends on the free energy of the rate limiting reaction. 9. The activity of pyruvate dehydrogenase (PDH) decreases: A. as the concentration of acetyl CoA increases. B. as blood insulin increases. C. as the concentration of pyruvate increases. D. as the concentration of NADH decreases. E. when the phospho-enzyme is converted to its dephosphorylated form. 10. Which enzyme would be impaired in a biotin deficiency? A. fructose 1,6-bisphosphatase. B. pyruvate kinase. C. PEP carboxykinase. D. pyruvate carboxylase. E. malate dehydrogenase 11. Which of the following is the correct sequence of carriers in the electron transport chain? A. NADH/CoQ reductase ® cytochrome c ® CoQ ® cytochrome reductase ® cytochrome oxidase. B. CoQ ® cytochrome reductase ® cytochrome oxidase ® cytochrome c ® NADH/CoQ reductase. C. NADH/CoQ reductase ® CoQ ® cytochrome reductase ® cytochrome c ® cytochrome oxidase. D. NADH/CoQ reductase ® CoQ ® cytochrome c ® cytochrome oxidase ® cytochrome reductase. E. NADH/CoQ reductase ® cytochrome reductase ® cytochrome c ® CoQ ® cytochrome oxidase. 12. The rate of glycolysis is increased by: A. insulin. B. ATP. C. citrate.

D. NADH. E. glucose 6-phosphate.

13. ATP is considered to be the universal source of energy for endergonic reactions but is not the storage form of energy under physiological conditions. Why? A. The actual free energy of hydrolysis of ATP is only -11 to -12 kcal. B. ATP is not located in the cytoplasm where most endergonic reactions occur. C. The half-life of ATP is too short. D. The synthesis rate for ATP is not efficient. 14. The viability of red blood cells is critically dependent on glycolysis as a source of energy. Glycolysis will cease if: A. the concentration of cAMP is decreased. B. phosphofructokinase is activated. C. mitochondria are not present in the cell. D. NADH is not oxidized. E. the concentration of AMP is increased.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 15. The first half of glycolysis involves which of the following? A. ATP synthesis at the substrate level. B. The incorporation of Pi into a triose phosphate. C. The reduction of NAD+ to NADH. D. The formation of 1,3-bisphosphoglycerate. E. Formation of triose phosphates from a hexose diphosphate. 16. Which statement is CORRECT? A. Enzymes are small molecules that are heat stable. B. Enzymes affect rates of reactions in the forward and reverse direction. C. Enzymes will determine whether a reaction will take place. D. Enzymes are permanently altered following the conversion of substrate to product. 17. Which of the following is present in the liver, but is absent in muscle? A. pyruvate carboxylase. B. glycogen synthetase. C. lactate dehydrogenase.

D. pyruvate dehydrogenase. E. glucose 6-phosphatase.

18. When are the concentrations of the conjugate acid and conjugate base equal? A. When the pH equals the pK. B. When the pH is 10X the pK. C. When the pH is 0.1X the pK. D. When the pH is 7.0. E. When the [H+] is equal to the [OH-]. 19. Patients with hemoglobin S are more resistant to malaria because: A. the protozoa causing malaria is not able to enter the erythrocytes due to an alteration of the membrane of the erythrocyte. B. the smaller size and the elongated shape of the erythrocyte prevents the protozoa from infecting other cells. C. the half-life of the erythrocyte is decreased in cells containing hemoglobin S resulting in a decrease level of the protozoa. D. hemoglobin S has a higher capacity to bind oxygen which inhibits the action of the protozoa. 20. What is the value of D Go' for the pathway A B C D? Reaction D Go' B A +5 kcal/mol C A +5 kcal/mol C D -15 kcal/mol A. +10 B. +5 C. -10 D. -15 E. -20 21. In aerobic glycolysis, NADH in the cytoplasm: A. is recycled by lactate dehydrogenase to produce NAD+ for glycolysis. B. reduces dihydroxyacetone phosphate to glycerol phosphate. C. reduces malate to oxaloacetate for transport into the mitochondrial matrix. D. can be transported into the mitochondrion by an NADH/NAD+ antiporter. E. acts as a negative allosteric effector for phosphofructokinase.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 22. Competitive inhibitors are commonly used in chemotherapy because: A. the inhibitors decrease the total amount of substrate. B. the inhibitors alter the enzymes when they bind and decrease the Vmax of the reaction C. the inhibitor resembles the structure of the product and inhibit the reaction by negative feedback. D. the inhibitor binds only to the active site and increases the Km. 23. The tricarboxylic acid cycle is initiated by the condensation of acetyl-CoA and: A. malate. B. citrate. C. pyruvate.

D. oxaloacetate. E. HCO3-.

24. Gluconeogenesis: A. is favored when insulin concentrations are high. B. occurs in the liver. C. allows skeletal muscle to produce free glucose. D. is stimulated by high levels of fructose 2,6-bisphosphate. E. uses acetyl CoA as a substrate. 25. Which of the following statements is TRUE? Enzyme catalysis of a chemical reaction: A. increases the energy of the transition state. B. decreases the change in free energy of the reaction. C. increases the change in free energy of the reaction. D. decreases the change in the free energy of activation. 26. The activity of which enzyme would be expected to increase as the level of insulin increases? A. Pyruvate dehydrogenase. B. Hexokinase. C. Glucose 6-phosphatase. D. Fructose 1,6-bisphosphatase. E. PEP carboxykinase. 27. Your patient has muscular weakness and degeneration of the optic nerve. Your tentative diagnosis is Leber's hereditary optic neuropathy. If this is the correct diagnosis, which of the following pathways will contain the defect? A. Tricarboxylic acid cycle. B. Electron transport. C. Glycolysis. D. Gluconeogenesis. E. Pyruvate dehydrogenase multienzyme complex. 28. Which of the following statements about enzyme substrate complexes is TRUE? A. At high substrate concentration the rate of the reaction is first order. B. The enzyme concentration is higher than the substrate concentration under physiological conditions. C. Alteration in the conformation of the enzyme may occur when substrate binds. D. Increase in enzyme concentration does not affect the rate of the reaction. 29. Which of the following is a physiological mechanism for regulating the catalytic activity of enzymes? A. Increasing the synthesis of the substrate. B. Covalent modification of tryptophan residues. C. Phosphorylation of histidine residues in the active site of the enzyme.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 D. Conformational alteration in the enzyme by binding regulatory proteins. 30. The synthesis of phosphoenolpyruvate from pyruvate: A. is the last step in glycolysis. B. is localized only in the cytosol. C. never occurs since the pyruvate kinase reaction is irreversible. D. consumes GTP. E. requires pyruvate kinase. 31. Which statement about non-competitive inhibitors is TRUE? A. Non-competitive inhibitors are not effective at high substrate concentrations B. Non-competitive inhibitors affect the Km of the reaction. C. Non-competitive inhibitors do not bind to the active site of the enzyme. D. Non-competitive inhibitors do not decrease the free energy of activation. 32. You are the team physician for your local women's soccer team. Some of your new recruits have been disabled due to injury for the past four months and are about to start a conditioning program. Since their aerobic fitness is crucial to the stamina needed for the game of soccer, you put them on a progressive interval running program. As their aerobic fitness increases, which of the following enzymes in their skeletal muscle do you expect to mirror that increase? A. Lactate dehydrogenase. B. PEP carboxykinase. C. Transaminase. D. Hexokinase. E. Succinate dehydrogenase. 33. The peptide bond: A. of a polypeptide chain is involved in the strong covalent bonds of the primary structure, as well as the weak, noncovalent hydrogen bonding interactions of any secondary structure. B. results from the condensation reaction between the alpha carboxyl group of one amino acid with the alpha amino group of a second amino acid. C. is the fundamental linking unit of amino acids that results in the primary structure of a polypeptide chain. D. results from condensation of any R-groups or side chains of different amino acids with each other. E. results in a somewhat rigid and planar structure. 34. Proteins are more likely to precipitate: A. at their pI value. B. at non-physiological salt levels. C. above their pI value. D. under the influence of agents that denature polypeptides by disruption of weak, non-covalent bonds that are essential for tertiary structure. E. under the influence of extremes of high temperatures. 35. Glycoproteins contain sugar residues covalently bonded to: A. lysine. B. threonine. C. leucine. D. asparagine. E. cysteine.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00

36. A patient complained of painful cramps in her legs during exercise. Her patient history also revealed that she experienced easy fatigability. Which of the following are consistent with these observations? A. The patient is diabetic. B. The patient is missing the enzyme glucose-6-phosphatase C. The patient may have a defective debranching enzyme. D. The patient may have a defective muscle phosphorylase. E. The patient had no liver glycogen. 37. When the arterial blood pH is 7.23, the plasma bicarbonate concentration is 10 meq/liter, and the PCO2 is 25 mm of Hg, (normal ranges: pH 7.35-7.45;HCO3- 21-28;PCO2 35-45) the acidbase disturbance is: A. Uncompensated respiratory acidosis B. Uncompensated metabolic acidosis C. Partially compensated metabolic acidosis D. Compensated metabolic acidosis E. Partially compensated respiratory acidosis 38. Concerning cholesterol biosynthesis: A. Two squalene units are required. B. The rate of synthesis is controlled by the rate of production of HMG-CoA. C. Oxygen is incorporated into the molecule at the C-17 position. D. NADPH is required for the formation of HMG-CoA. E. HMG-CoA reductase is stimulated by insulin. 39. Facilited diffusion: A. requires energy in the form of ATP. B. can transport a solute against a concentration gradient. C. is not subject to competitive inhibition. D. displays no specificity. E. displays saturation kinetics. 40. Pernicious anemia is caused by: A. a deficiency of dietary vitamin B12 B. a deficiency of dietary folic acid C. an excess production of HCl by the parietal cells of the stomach. D. a deficiency of intrinsic factor. 41. How does the cell maintain a higher level of K+ than of Na+? A. The Na+ leaks out into the surrounding extracellular fluid. B. K+ is bound to sites inside the cell. C. The body contains less total Na+ than K+, so Na+ is found at a low concentration inside the cell. D. Na+ is actively transported out of the cell and K+ actively transported into the cell. E. Much of the Na+ outside the cell is bound to protein, so that no Na+ gradient exists across the cell membrane. 42. In the biosynthesis of purines the first purine derivative formed is: A. inosine. B. inosine monophosphate. C. guanosine monophosphate. D. adenosine monophosphate.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 E. xanthosine monophosphate. 43. An amino acid which is both ketogenic and glucogenic is: A. tyrosine. B. alanine. C. leucine.

D. glutamate. E. histidine.

44. Which one of the following compounds is a COMMON intermediate in ketogenesis and cholesterogenesis? A. mevalonic acid B. acetoacetic acid C. succinyl-CoA

D. HMG-CoA E. malonyl-CoA

45. Hyaluronic acid consists of repeating units of: A. glucose and fructose. B. glucuronic acid and N-acetylglucosamine. C. galactose and N-acetylgalactosamine. D. glucuronic acid and N-acetylgalactosamine. E. glucuronic acid and N-acetylgalactosamine-4-sulfate. 46. Enzyme distribution among tissues varies according to the function of the tissue. Which of the following is absent in muscle, but is present the liver? A. hexokinase. B. glucose 6-phosphatase. C. lactate dehydrogenase.

D. pyruvate dehydrogenase. E. glycogen phosphorylase.

47. The following are true statements about proteins in biological membranes EXCEPT: A. Proteins in membranes can be attached either peripherally or penetrate, even span, the lipid bilayer. B. They are usually asymmetrically distributed on the different sides of the bilayer. C. They are involved in transport processes through the lipid bilayer without changing sides (flip-flop) from one side to the other. D. They are immobile and fixed to the surrounding lipids. E. Integral proteins usually contain a sequence of hydrophobic amino acids arranged as alphahelix or beta-sheets. 48. Chronic alcohol intake will elevate the chylomicrons in blood. Which one of the following is a normal constituent of chylomicrons? A. apoB-100 B. triglycerides C. lipoprotein lipase

D. free fatty acids.

49. Which of the following enzymes would show the greatest increase in serum activity in viral hepatitis? A. creatine kinase B. alkaline phosphatase C. alanine aminotransferase

D. 5' nucleotidase E. acid phosphatase

50. Which of the phospholipids is deficient in the lungs of patients with ARDS (acute respiratory

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 A. ADP syndrome)? distress D. ATP A. magnesium B. phosphatidylcholine. ions E. calcium ions B. inorganic C. phosphatidylinositol. phosphate C. phosphatidic acid. D. cardiolipin. 55. As regards receptors coupled to Gs (stimulatory G protein) and cAMP, which of the E. sphingomyelin. following is FALSE? A. Binding of a hormone to its receptor activates an enzyme which catalyzes 51. displacement the Increased excretion of GDP ofwith urobilinogen GTP on the in the alpha urine Gs is subunit. most commonly the result of A. The B. hemolysis. Gs alpha subunit dissociates from the beta/gamma subunits and activates adenylate B. erythropoetic porphyria. cyclase. C. Adenylate liver disease cyclase such as catalyzes viral hepatitis. the conversion of ATP to cAMP. D. cAMP iron deficiency. activates cAMP dependent protein kinase by binding to the regulatory subunits which E. bile dissociation causes duct obstruction. of the regulatory subunits from the catalytic subunits. E. The catalytic subunit of cAMP dependent protein kinase phosphorylates proteins on serine. 52. Which of the following statements about the pentose phosphate pathway is INCORRECT? A. Pentoses 56. The onlycan apoprotein be formed in LDL both oxidatively is: and non-oxidatively. B. This pathway is important to fatty acid synthesis because it produces reducing equivalents. C. Fructose A. Apo A 6-phosphate can be used to make ribose D. 5-phosphate. Apo D D. Apo B. Glyceraldehyde B-100 3-phosphate can be used to makeE. ribose Apo 5-phosphate. B-48 E. NADH C. Apo CIIis formed by the action of glucose 6-phosphate dehydrogenase. 57. The 53. For transport "methyl trap" across hypothesis the inner states mitochondrial that in the membrane, absence oflong vitamin chainB12, fattythere acidsisare a block attached in the to: further metabolism of A. coenzyme N5-methylA. tetrahydrofolate (THF) monoglutamate. D. acyl transferase. B. acyl N5,10-methylene transacylase. THF. E. carnitine. C. phosphatidylethanolamine. N10-formyl THF. D. N5,10-methenyl THF. E. dihydrofolate. 58. The activity of lipoprotein lipase is stimulated by: A. APO A 54.APO B. ActinB-48 is released from its interaction with myosin by the addition of: C. APO CII D. APO E E. APO B-100 59. A major contributing factor to cataract formation in diabetes may be the accumulation of sorbitol in the lens. For that to occur, glucose has to interact with: A. hexokinase and phosphoglucose isomerase B. fructose dehydrogenase C. aldose reductase D. hexokinase and glucose 6-phosphate dehydrogenase E. glucose oxidase 60. The sphingolipidoses are a group of diseases involving defective breakdown of ceramides. Which one of the following is characteristic for a ceramide? A. an N-linked fatty acid residue B. a residue of glycerol. C. a phosphorylcholine residue D. three fatty acid residues E. contains a thiol 61. The rate-limiting step in the conversion of cholesterol to bile acids is A. side chain oxidation. B. 12-alpha-hydroxylation. C. 7-alpha-hydroxylation.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 D. 7-beta-hydroxylation. E. conversion to coprostanol. 62. Primaquine sensitivity is a result of a defect in the pentose phosphate pathway. Which of the following is TRUE for the pentose phosphate pathway: A. It is absent in red blood cells. B. Its regulated step is catalyzed by glucose-6-phosphate dehydrogenase. C. It channels all glucose carbons into the production of ribose. D. It can provide the cell with NADH needed in the synthesis of fatty acids. E. One of its functions is to maintain cellular glutathione in the oxidized state. 63. Most urinary ammonium ions are derived by the enzymatic hydrolysis of: A. glutamine. B. glutamic acid. C. histamine. D. 6-amino purine derivatives. E. urea. 64. The rate-limiting enzyme in cholesterol biosynthesis is: A. isopentyl pyrophosphate isomerase. B. mevalonate kinase. C. hydroxymethylglutaryl-CoA reductase. D. dimethylallyl transferase. E. squalene synthase. 65. Which one of the following enzymes is involved in the hydrolysis of triglycerides found in chylomicrons? A. lipoprotein lipase B. fatty acyl CoA transferase C. hormone sensitive lipase D. pancreatic lipase E. cholesterol ester transfer protein 66. A genetic disease characterized by accumulation of excess phenylalanine in the tissues, mental retardation, and excretion of phenylalanine metabolites in the urine is caused by a deficiency in A. phenylalanine transaminase. B. tyrosine transaminase. C. phenylalanine hydroxylase. D. homogentisic acid oxidase. E. phenylalanine decarboxylase. 67. The creatine kinase isoenzyme which is characteristic of heart muscle is: A. the MB isoenzyme. B. the MM isoenzyme. C. the BB isoenzyme.

D. the CK isoenzyme.

68. A patient with a deficiency in the enzyme, thioesterase, is unable to release a fully formed fatty acid from fatty acid synthase. The name for that fatty acid is: A. arachidonic acid B. an omega 3 fatty acid C. octadecanoic acid

D. palmitic acid E. stearic acid

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00

69. Which one of the following factors is NOT essential for the conversion of prothrombin to thrombin in the clot cascade? A. Ca ion B. Factor X C. Phospholipid

D. Factor V E. Factor XIII

70. A DNA deletion occurs 1000 bp upstream of the src protooncogene, causing it to be activated. The sequence deleted is probably a(n): A. promoter. B. operator. C. enhancer.

D. silencer. E. initiator.

71. Which of the following is NOT a possible consequence of a single nucleotide deletion in the coding region of an exon? A. Change in reading frame. B. Diminution of polyadenylation. C. Deletion of the 5' splice site. D. Nothing (i. e., no consequence). E. Loss of the start codon. 72. Which of the following enzymes are NOT used in cDNA cloning? A. RNA polymerase. B. DNA polymerase. C. Reverse transcriptase.

D. Restriction endonuclease. E. DNA ligase.

73. Which statement best describes, "junk" DNA? A. Some "junk" DNA may have a function. B. It is never transcribed into RNA. C. It consists of short repeated sequences of DNA. D. Pseudogenes never have introns. E. All pseudogenes contain Alu sequences. 74. Which of the following statements is NOT true of PCR? A. It is useful in the diagnosis of certain genetic disorders. B. It requires stringent laboratory precautions to ensure its validity. C. RT-PCR requires the use of the enzyme reverse transcriptase during cDNA synthesis. D. Use of thermostable DNA polymerases have greatly aided in its usefulness. E. Only one primer is required. 75. Which of the following proteins can introduce positive supercoils into DNA? A. Primosome. B. DNA ligase. C. Helicase. D. Single strand-binding protein. E. XPF protein. 76. A mutation that allows read-through of a stop codon during translation is called a ______ mutation. A. termination.

B. transversion.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 C. amber. D. suppressor.

E. silencer.

77. The gene for albumin is highly expressed in the liver; which of the following is LEAST likely about the chromatin near that gene? A. The albumin gene is in a region of euchromatin in liver. B. The DNA is highly methylated at pCpG sequences in the region. C. Histones are less abundant in the region. D. Histones are acetylated in the region. E. A and C. 78. Which of the following is NOT a general feature of enhancers? A. Distance independence. B. They are found in prokaryotes and eukaryotes. C. Orientation independence. D. The proteins that bind them generally function as dimers. E. B and C. 79. The first three nucleotides of a palindromic restriction endonodease recognition sequence are 5'-AAG-3'. What is the entire six basepair recognition sequence (both strands)? A. 5'-AAG-3' 3'-TTC-5' B. 5'-AAGCTT-3' 3'-TTCGAA-5' C. 5'-AAGCTT-3' 5'-TTCGAA-3' D. 5'-AAGGAA-3' 3'-TTCCTT-5' E. None of the above. 80. You have determined that a strand of DNA is GC-rich. Its complementary strand is: A. AT-rich. B. pyrimidine-rich. C. purine-rich. D. GC-rich. E. cannot determine from the information given. 81. You have incorporated a radioactive "label" into a PCR primer. After 30 cycles of PCR, the radioactivity will be found: A. only in the original target DNA molecules. B. in 50% of the new DNA molecules. C. interspersed between the parent and child strands of both new DNA molecules. D. in 100% of the new DNA molecules. E. A and D. 82. Which of the following statements is FALSE about eukaryotic chromosome structure? A. Centromeres contain alphoid repeats. B. Protein scaffold required for complete compaction. C. High telomerase activity has been associated with some cancers. D. Mitochondrial chromosomes sometimes contain short telomeres. E. Mitochondrial genes sometimes use a different genetic code. 83. Increased plasma insulin can result in: A. increased adipocyte adenylate cyclase activity. B. decreased hepatocyte glucokinase

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 C. decreased hepatocyte glycogen. D. decreased hormone sensitive lipase activity. E. decreased hepatocyte pyruvate dehydrogenase activity. 84. All the following substances are potentially mitogenic EXCEPT: A. Platelet-derived growth factor. B. Insulin. C. Exocrine factors. D. Contact inhibition. E. Steroid hormone. 85. A chronic alcoholic is admitted to your service with a blood pH of 7.2. Which of the following explains this finding? A. Ethanol is an acid that produces acidosis when consumed in large quantities. B. Ethanol is converted into lactic acid that will lower blood pH. C. Ethanol elevates the NADH concentrations in the liver causing an increased conversion of pyruvate to lactate. D. Ethanol decreases the respiratory rate leading to a buildup of CO2 that is converted to carbonic acid. E. Ethanol blocks electron transport causing a buildup of NADH and lactate. 86. Which immune response would be considered an immune system dysfunction? A. Successful vaccination against rabies virus. B. Organ transplant rejection. C. Immune response to influenza virus. D. An autoimmune response. E. Successful vaccination against poliovirus. 87. Glucagon plays a homeostatic role by: A. increasing in response to elevated blood glucose levels and then activating liver glycogen synthetase. B. increasing in response to lowered blood glucose levels and then activating liver glycogen phosphorylase. C. stimulating the release of glucose residues from muscle glycogen during intense exercise. D. activating adenylate cyclase in skeletal muscle cells. E. facilitating glucose uptake into skeletal muscle. 88. All of the following are likely to occur after eating a large amount of carbohydrate EXCEPT: A. the synthesis of triacylglycerol in the liver. B. the synthesis of glycogen in the liver. C. increased pentose phosphate pathway activity in liver. D. release of glycerol from adipose tissue. E. the synthesis and release of VLDL from the liver. 89. Which of the following statements is TRUE about antigen-antibody reactions? A. They are not involved in allergic responses. B. They function to identify antigens for subsequent removal from the body. C. They occur because of the complementarity between epitope and parasite. D. They occur because of complementarity between alpha helices and beta turn structures. E. They only involve proteins. 90. The enzyme in liver that is stimulated first by glucagon is: A. phosphofructokinase B. glycogen synthase C. hormone sensitive lipase

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 D. protein kinase A E. isocitrate dehydrogenase 91. Which statement below is TRUE about antibodies? A. Antibodies are normally made against nucleic acids. B. Antibodies all require J-chains. C. Antibodies are lipoproteins. D. Antibodies are cytokines produced by plasma cells. E. All antibodies are composed of heavy chains and light chains. 92. 1,25-dihydroxycholecalciferol (calcitriol): A. is produced by the liver. B. inhibits resorption of calcium ions from bone. C. promotes intestinal synthesis of a calcium binding protein. D. reduces absorption of calcium from the kidney. E. synthesis is reduced by parathyroid hormone. 93. Which of the following is exhibited by diabetics WITHOUT insulin therapy? A. An increase in the rate of VLDL synthesis by the liver. B. An increase in the rate of oxidation of fatty acids by the liver. C. An increase in the rate of protein synthesis in muscle. D. An increase in the conversion of alanine to pyruvate in skeletal muscle. E. An increase in the use of acetone as energy by the brain. 94. Your patient has a genetic defect that blocks the synthesis of androstenedione. Which of the following will also be reduced by this defect? A. progesterone. B. testosterone. C. pregnenolone. D. cortisol. E. aldosterone.

95. Which of the following statements below is FALSE? A. Histocompatibility antigens are cell surface protein structures capable of presenting antigenic fragments to T-cells for specific recognition by T-cells. B. Class switching changes the immunoglobulin class, but not the paratope. C. Antibody paratopes result from the juxtaposition six hypervariable regions, three each from the light chain and the heavy chain variable domains. D. B-cells synthesize heavy chains, light chains and secretory piece. E. The five major immunoglobulin classes are IgM, IgG, IgD, IgE, and IgA. 96. In the fed state: A. glucose is both converted to glycogen and stored in skeletal muscle. B. adipose tissue converts triglycerides to glucose. C. amino acids are transaminated to form ketone bodies. D. glycogen stores in liver are depleted. E. glycogen phosphorylase is in the active form. 97. Which of the following statements is FALSE? A. Immunogens are normally viewed as foreign by the immune system.

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BIOCHEMISTRY Physician Licensure Examination June 3, 2008; 8:00 – 12:00 B. Antigens are almost always high molecular weight lipids or carbohydrates. C. Antigens can be parts of parasites, bacteria or viruses. D. Epitopes of proteins are generally five to six amino acids in size. E. Antigens have small topological features called epitopes. 98. Chronic alcohol consumption: A. leads to decreased NADH production in the cytosol and mitochondria. B. leads to hyperglycemia because alcohol is converted to glucose. C. leads to decreased rates of inactivation of drugs by cytochrome P450. D. leads to decreased concentrations of pyruvate in the liver. E. leads to increased chylomicron production by the liver 99. All of the statements below about T-cells are TRUE, EXCEPT which one? A. The T-cell antigen receptor specifically recognizes the antigen fragment carried by the major histocompatibility complex class I protein. B. The major histocompatibility complex class I protein is recognized by the CD8 (or T8) protein of the cytotoxic T-cell. C. The T-cell antigen receptor is a heterodimeric protein with variable region domains and constant region domains. D. The major histocompatibility complex class II protein is recognized by the CD4 (or T4) protein of the helper T-cell. E. The CD3 complex of the T-cell carries and displays the antigen fragment. 100. Twenty four hours after a meal, the primary source of glucose carbons for the brain is: A. dietary glucose. B. muscle glycogen. C. glycerol from adipose tissue. D. fatty acids. E. skeletal muscle protein.

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