FIRST INTRASESSIONAL EXAMINATION C MEDICAL 1997 Page 1

1. Which of the following statements about spontaneity is correct?
1. All reactions with D GEN < 0 will be spontaneous.
2. All reactions which have D H < 0 will be spontaneous.
3. All reactions for which D G is not equal to zero will be spontaneous.
4. All reactions for which have D G < 0 will be spontaneous.
5. All reactions for which have D S < 0 will be spontaneous.
2. For the reaction

A º B + C

D GEN = -2.00 kcal/mol. What is D G at 25EC if the concentration of each of the three reacting species is 1 M? (NOTE: 2.3 X 1.987 X 298 = 1.36; log 1.36 = 0.13)

1. -3.36 kcal/mol
2. -2.13 kcal/mol
3. -2.00 kcal/mol
4. +2.00 kcal/mol
5. +2.13 kcal/mol
3. An important characteristic of living systems is that
1. They are always at equilibrium.
2. They are perturbed from equilibrium only when experiencing stress.
3. They are never at equilibrium.
4. They are at equilibrium only when metabolic activity is low.
5. The laws of thermodynamics do not apply.
4. All the following statements about ATP are correct EXCEPT
1. ATP has two phosphoanhydride bonds.
2. ATP has one phosphate ester bond.
3. ATP has a D GEN of hydrolysis.
4. ATP is usually complexed with Mg²⁺.
5. ATP has three high energy bonds.
5. All the following compounds are high energy compounds EXCEPT
1. acetyl coenzyme A
2. creatine phosphate
3. glucose-6-phosphate
4. phosphoenolpyruvate
5. ADP
6. The large negative value for D GEN of hydrolysis of phosphoenolpyruvate is primarily due to
1. hydrolysis of a phosphoanhydride bond
2. hydrolysis of a phosphate ester bond
3. the combined effect of hydrolysis and subsequent conversion of the keto form of pyruvate to the enol form
4. the combined effect of hydrolysis and subsequent conversion of the enol form of pyruvate to the keto form
5. hydrolysis of a thiol ester bond
7. For glucokinase, K_m = 10 mM, while for hexokinase, K_m < 0.1 mM. These data are consistent with which of the following statements?
1. Hexokinase acts only at low blood glucose levels.
2. Glucokinase acts only at high blood glucose levels.
3. Glucokinase plays a major role in glucose metabolism only at low levels of blood glucose.
4. Hexokinase acts only at high levels of blood glucose.
5. Glucokinase can effectively remove enzyme-bound glucose from hexokinase.
8. The enzyme catalyzing the reaction that commits glucose to glycolysis is
1. hexokinase.
2. phosphoglucoisomerase.
3. phosphofructokinase-1.
4. aldolase.
5. phosphotriose isomerase.
9. All of the following are true of phosphofructokinase-1 EXCEPT?
1. Phosphofructokinase-1 is an allosteric enzyme.
2. Citrate increases the activity of phosphofructokinase-1.
3. AMP increases the activity of phosphofructokinase-1.
4. Phosphofructokinase-1 is subject to regulation by covalent modification.
5. Glucagon indirectly lowers the activity of phosphofructokinase-1.
10. Substrate-level phosphorylation occurs in glycolysis in the reaction catalyzed by
1. hexokinase
2. phosphofructokinase-1
3. phosphoglycerate kinase
4. glyceraldehyde-3-phosphate dehydrogenase
5. aldolase
11. Binding of glucagon to its receptor leads to adenylate cyclase-catalyzed synthesis of c-AMP, which activates protein kinase A. This leads to:
1. Dephosphorylation of PFK-2/F-2,6-bisphosphatase, hydrolysis of F-2,6-BP, and decrease in glycolytic activity
2. Dephosphorylation of PFK-2/F-2,6-bisphosphatase, hydrolysis of F-2,6-BP, and increase in glycolytic activity
3. Phosphorylation of PFK-2/F-2,6-bisphosphatase, synthesis of F-2,6-BP, and decrease in glycolytic activity
4. Phosphorylatlon of PFK-2/F-2,6-bisphosphatase, hydrolysis of F-2,6-BP, and decrease in glycolytic activity
5. Phosphorylatlon of PFK-2/F-2,6-bisphosphatase, hydrolysis of F-2,6-BP, and increase in glycolytic activity
12. In anaerobic glycolysis from glucose to lactate, how many net moles of ATP and how many net moles of NADH are produced for each mole of glucose?

ATP NADH

A) 0 2

B) 2 0

C) 2 2

D) 4 0

E) 4 2

13. All of the following statements about the pyruvate dehydrogenase complex are correct EXCEPT?
1. Pyruvate dehydrogenase is inhibited by acetyl CoA and NADH.
2. Pyruvate dehydrogenase is activated by dephosphorylation and inactivated by phosphorylation.
3. The reaction catalyzed by the pyruvate dehydrogenase complex requires TPP, NAD⁺, FAD and 2,3 bisphosphoglycerate.
4. The products of the reaction catalyzed by the pyruvate dehydrogenase complex are acetyl CoA, CO₂, and NADH.
5. Genetic pyruvate dehydrogenase deficiency may be treated with dichloroacetate.
14. Oxidation of one molecule of pyruvate by pyruvate dehydrogenase and one turn of the TCA cycle results in net formation of how many molecules of each of the following?

GTP NADH FADH₂ CO₂

A) 1 3 1 2

B) 1 3 2 3

C) 1 4 1 2

D) 2 4 1 3

E) 1 4 1 3

15. NADH is generated in reactions catalyzed by all the following enzymes EXCEPT
1. Pyruvate dehydrogenase complex.
2. Isocitrate dehydrogenase.
3. α-ketoglutarate dehydrogenase complex.
4. Succinate dehydrogenase.
5. Malate dehydrogenase.
16. Citrate synthase is inhibited by all of the following EXCEPT
1. pyruvate
2. ATP
3. NADH
4. succinyl CoA
5. long-chain acyl CoA derivatives
17. All of the following are true of the TCA cycle EXCEPT
1. as a result of anaplerotic reactions, both substrates for the TCA cycle can come from pyruvate.
2. α-ketoglutarate can be regenerated by the action of glutamate dehydrogenase.
3. the committed step is catalyzed by citrate synthase.
4. normal operation of the TCA cycle results in no net yield of oxaloacetate.
5. the TCA cycle is a strictly catabolic pathway.
18. The two molecules of CO₂ produced in one round of the TCA cycle are derived directly from
1. the carboxyl carbons from the acetyl group that entered the cycle in this round
2. the carboxyl groups in oxaloacetate
3. the non-carboxyl groups in oxaloacetate
4. the methyl carbon in the acetyl group that entered the cycle in this round
5. chemically non-identical groups in oxaloacetate
19. The family of cytochromes P-450 are not considered to be isozymes because
1. different P-450's have different substrate specificities.
2. some P-450's are inducible and some are constitutive.
3. some P-450's are microsomal and some mitochondrial.
4. some P-450's require a pyridine nucleotide (NAD(P)H) for activity, and some do not.
5. all P-450's have the same primary sequence.
20. Cytochrome P-450 plays a role in carcinogenesis because
1. it binds CO.
2. it can inactivate therapeutic drugs.
3. it can form a reactive compound from an inert one.
4. one of its products is the hydroxyl radical.
5. some bacteria also contain cytochrome P-450.
21. Liver cytochrome P-450 is the terminal electron acceptor of a microsomal electron transport chain. Which molecule(s) donates electrons directly to the heme iron in this system?
1. FADH₂/FMNH₂
2. NADPH + H⁺
3. NADH + H⁺
4. Iron-sulfur proteins
5. Water
22. The cleavage of xanthine oxidase during ischemia causes
1. ATP degradation to hypoxanthine.
2. Ca⁺⁺ dependent-protease activation.
3. formation of O^$₂^B as a product of the xanthine oxidation reaction
4. loss of membrane integrity
5. massive Ca⁺⁺ influx
23. Which of the following enzymes can catalyze the same reaction as catalase?
1. Cytochrome P-450
2. Glutathione peroxidase
3. Glutathione reductase
4. Peroxidase
5. Superoxide dismutase
24. 0.1 ml of a bacterial culture of 10⁸ cells/ml are plated on a restrictive medium (i.e. only revertants can grow). If the spontaneous mutation rate is 1 in 10⁶, how many colonies, on average, would be seen on a plate?
1. none
2. 1
3. 10
4. 100
5. 1000
25. A compound shown to be a mutagen in the Ames Test may not be a carcinogen in man for any of the following reasons EXCEPT
1. human and bacterial DNA do not undergo mutation by the same mechanism
2. mammalian DNA has additional protective protein.
3. mammalian DNA is in the nucleus.
4. mammals may have a more active DNA repair mechanism.
5. the compound may be rapidly removed by the excretory system.
26.  

 

The hydrolyzed dipeptide shown here on a TLC plate is either gly-lys or lys-gly. Which of the following is a possible pair of products from dansylation followed by hydrolysis?


1. Didansylated gly, mono-dansylated lys
2. Gly, monodansylated lys
3. Gly, didansylated lys
4. Lys, monodansylated gly
27. Which of the following has the lowest pH?
1. Bleach
2. Coca Cola
3. Lemon Juice
4. Tomato Juice
5. Vinegar
28. An ε-amino group is part of the sidechain of
1. Arg
2. Asn
3. Lys
4. Tyr
5. Trp
29. A carboxyamide group is part of the sidechain of
1. Arg
2. Asp
3. Gln
4. Glu
5. Ile

Use the following sequence for the peptide neurotransmitter β-endorphin to answer questions 30 and 31.

Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe- Lys-Asn-Ala-Ile-Ile-Lys-Asn-Ala-Tyr-Lys-Lys-Gly-Glu

30. At pH 7.5 β-endorphin has an approximate net charge of
1. 3
2. 2
3. 1
4. -1
5. -2
31. Treatment of β-endorphin with cyanogen bromide generates how many peptide fragments?
1. 5
2. 4
3. 3
4. 2
5. 1 (does not cleave)
32. Which are the thrombin cleavage products of the peptide

Met-Gly-Tyr-Met-Phe-Arg-Gly-Asp-Lys-Glu-Trp ?

1. Met-Gly-Tyr, Met-Phe, Arg-Gly-Asp-Lys-Glu-Trp
2. Met-Gly-Tyr-Met-Phe-Arg, Gly-Asp-Lys-Glu-Trp
3. Met-Gly-Tyr-Met-Phe-Arg, Gly-Asp-Lys, Glu-Trp
4. Met, Gly-Tyr-Met, Phe-Arg-Gly-Asp-Lys-Glu-Trp
5. Thrombin cannot cleave this peptide.
33. Each of the following amino acid residue types may become post-translationally glycosylated EXCEPT
1. Asn
2. Hyl
3. Leu
4. Ser
5. Thr
34. Which of the following amino acid point mutations would be considered the most conservative in the evolution of the primary sequence of a protein?
1. His to Pro
2. Ile to Val
3. Glu to Gln
4. Ala to Ser
5. Lys to Leu
35. All of the following statements are true of the α-helix EXCEPT it
1. contains 3.0 residues per turn.
2. is the component secondary structure of the EF-hand.
3. is stabilized by H-bonds parallel to the helical axis.
4. often forms the transmembrane segment of membrane associated proteins.
5. usually has a right-handed sense in proteins.
36. The reduction of disulfide bonds in proteins may be accomplished by treatment with which of the following?
1. Guanidine-HCl (6M).
2. HCl (6N).
3. 2-mercaptoethanol.
4. Performic acid.
5. Urea (8M).
37. Complete denaturation of protein structure generally may be accomplished with which of the following?
1. Ammonium nitrate
2. Cyanogen bromide
3. Dinitrofluorobenzene (8M)
4. 2-mercaptoethanol
5. Urea (8M)
38. Peptide sequencing via the Edman degradation procedure employs
1. dansyl chloride.
2. dinitrofluorobenzene.
3. fluorescamine.
4. ninhydrin.
5. phenyl isothiocyanate.
39. Point mutation within an epithelial transmembrane receptor protein has been strongly implicated in which of the following diseases?
1. Cystic fibrosis
2. Ehlers-Danlos syndrome
3. Marfan's syndrome
4. Diabetes
5. Premature emphysema
40. Which of the following proteins contains calcium binding EF-hand motifs?
1. Hemoglobin
2. Insulin
3. α-keratin
4. HIV-1 protease
5. Troponin C
41. Reduced lysyl amino oxidase activity within an individual would likely result in
1. diminished crosslinking of collagen.
2. increased production of allysine derivatives in procollagen.
3. increased Schiff base formation in procollagen.
4. reduced collagen polypeptide synthesis.
5. reduced hydroxylation of lysine in procollagen
42. During collagen synthesis events that occur extracellularly include all of the following EXCEPT
1. alignment of collagen molecules into macrofibers.
2. cleavage of amino and carboxyl terminal peptides.
3. covalent crosslinking of molecules.
4. creation of allysyl residues.
5. hydroxylation of prolyl residues.
43. All of the following exhibit coiled-coil structure EXCEPT
1. fibrinogen.
2. α-keratin.
3. leucine zipper proteins.
4. procollagen.
5. tropomyosin.
44. All of the following are true of immunoglobulin molecules EXCEPT
1. glycosylation within the F_c region can occur.
2. heavy chain identity determines the immunoglobulin class.
3. hypervariable sequences of the F_ab fragments determine antigenic specificity.
4. papain treatment completely separates light and heavy chains
5. pepsin treatment leaves a bivalent fragment.
45. The major immunoglobulin class present in plasma is
1. IgG.
2. IgA.
3. IgM.
4. IgD.
5. IgE.
46. Carbon dioxide is bound to hemoglobin by
1. binding at the cleft between the beta subunits of adult hemoglobin.
2. carboxylation of glutamic acid residues.
3. formation of carbamino groups on N-terminal α-amino groups.
4. interaction between the heme iron and a histidine of the globin chain.
5. reaction with the carboxyethyl groups of the heme.
47. The Bohr Effect associated with increased oxygen delivery to tissues when pH decreases is best explained by
1. carbon dioxide binding to hemoglobin and decreasing oxygen affinity.
2. increased hemoglobin affinity for O₂ resulting in polycythemia.
3. oxyhemoglobin having a lower pK_a for the side chain of an amino acid residue than deoxyhemoglobin.
4. the high affinity of CO for the oxygen binding site.
5. the uptake of chloride ions by the red blood cell under high CO₂ tension.

Use the following figure showing globin chain production during human development to answer question 48.

48. (Figure not available)
49. The curve that best describes the synthesis of the γ-globin (gamma) chain during development.
1. A
2. B
3. C
4. D
5. E
50. Chronic hypoxia at high altitude would produce one of the following compensatory changes in the oxygen transport system.
1. A greater deoxygenation of hemoglobin would occur at the capillaries.
2. Decreased red cell sickling in sickle cell disease.
3. Erythrocytic 2,3-bisphosphoglycerate would decrease.
4. Myoglobin concentration would decrease in skeletal muscle.
5. The blood hematocrit would decrease.
51. Anemias could be caused by all of the following conditions EXCEPT
1. α- and β-thalassemia.
2. conversion of hemoglobin to methemoglobin.
3. dietary iron deficiency.
4. increased circulating erythropoeitin.
5. the Asickling@ of HbS at low oxygen tension.
52. β-Thalassemia in homozygous individuals is characterized by
1. a defect in α-globin production and a mild anemia with resistance to lethal forms of malaria.
2. death in utero (Hydrops fetalis).
3. high circulating levels of methemoglobin.
4. polymerization of hemoglobin induced at low oxygen tension.
5. the precipitation of highly insoluble monomeric α-globin in red blood cells.
53. All of the following are true concerning 2,3-bisphosphoglycerate (2,3-BPG) EXCEPT
1. Significant amounts of 2,3-BPG is produced only within the red blood cell.
2. Increases in 2,3-BPG could occur in response to hypoxia in body tissues.
3. Sickling of erythrocytes in HbS disease would be promoted by increased intracellular levels.
4. 2,3-BPG is derived from 1,3-BPG, an intermediate of glycolysis.
5. 2,3-BPG binds to hemoglobin A₁ causing a decrease in its P₅₀.
54. The ammonia secreted in urine during chronic acidosis is derived most directly from
1. arginine.
2. aspartate.
3. glutamate.
4. glutamine.
5. glycine.
55. A patient with chronic obstructive lung disease had a blood pH of 7.2; PCO₂ , 70 mm Hg; [HCO₃^-], 29.8 meq. L^-1. The condition of the patient is best described as

{PCO₂ x 0.0301 = [H₂CO₃, mM]; PCO₂ = 40 mm (normal);

[HCO₃^-] (normal) = 24 meq L^-1}

1. Metabolic acidosis, completely compensated.
2. Respiratory acidosis, completely compensated.
3. Respiratory acidosis, partially compensated.
4. Respiratory alkalosis, compensated.
5. Metabolic alkalosis, completely compensated.
56. If the pK_a of an amino group in the microenvironment of a protein is 8.4, what is the ratio of the conjugate base to the conjugate acid at pH 7.4?
1. 1:100
2. 100:1
3. 10:1
4. 1:10
5. 1:1000
57. All of the following pairings concerning blood components are correct EXCEPT
1. The major iron-containing protein of the body - hemoglobin.
2. The major carbon dioxide transporter - hemoglobin.
3. The major oxygen transporter - hemoglobin.
4. The major physiological buffer - HCO₃^-/CO₂ system.
5. The major source of plasma osmolarity - Na⁺, HCO₃^-, Cl^-.
58. A high anion gap would be present in all of the following acidotic conditions EXCEPT
1. diabetic ketoacidosis.
2. diarrhea
3. ingestion of a weak organic acid.
4. ingestion of toxins : methanol, ethylene glycol
5. lactic acidosis.
59. The dietary guideline of the American Institute for Cancer Research that recommends a reduction in the intake of dietary fat is specifically aimed at reducing the risk of cancer of the
1. breast and colon.
2. liver and mouth.
3. mouth and larynx.
4. stomach and esophagus
60. The new Recommended Dietary Allowances (RDA=s) will differ from previous RDA=s in that they will
1. be based on avoidance of deficiency disease.
2. make recommendations for pregnant and lactating women.
3. place emphasis on the beneficial effects of nutrients that will optimize health.
4. reflect different requirements for different age groups.
5. take gender into consideration when establishing the recommendations for nutrient intake.
61. What is the percentage of calories that come from fat in the food that bears the label below? (Figure not available)
1. 4
2. 6
3. 9
4. 30
5. 35
62. Which of the items in column one is a correct match for the item in column two?

 

Column One	Column Two
A. Extrinsic pathway requires	Prekallikrein
B. Intrinsic pathway requires	Tissue factor
C. Protein C's substrates	Factors Xa and XIIa
D. Gla-peptides from prothrombin stimulate	de novo synthesis of other Gla-containing factors
E. Thrombin's substrate	Plasminogen

 

63. Which of the following statements is correct for enzymes that obey Michaelis-Menten kinetics?
1. Km is defined by (k₂+k₃)/k₁ and is dependent on enzyme concentration.
2. The initial velocity phase of an enzyme reaction occurs when [ES] changes with time.
3. The presence of a competitive inhibitor will affect both the slope and the y-intercept of a Lineweaver Burk plot.
4. The presence of a non-competitive inhibitor will affect only the x-intercept of a Lineweaver-Burk plot.
5. Vmax is defined by k₃[ES] and occurs when [ES] equals [Et].
64. An enzyme that is involved in the regulation of a metabolic pathway will generally show which one of the following properties?
1. a plot of v versus [S] in the presence of an inhibitory ligand (metabolic regulator) will resemble that for negative cooperativity between subunits.
2. a plot of v versus [S] will not vary from that seen normally for Michaelis-Menten kinetics.
3. the amount of substrate required to increase the rate from 10% to 90% of Vmax is very large (approximately an 80-fold change).
4. the enzyme will be responsible for catalyzing the first reversible step in the metabolic pathway.
5. the Hill coefficient is greater than one.
65. The Michaelis-Menten equation in the presence of a competitive inhibitor is v = (VmaxS)/{Km(1+I/Ki) + S}. At a substrate concentration equal to the Km and an inhibitor concentration equal to the Ki, the relative rate (fraction of Vmax) is
1. 0.25
2. 0.33
3. 0.50
4. 0.67
5. 0.75
66. Each of the following statements about isoenzymes (isozymes) is correct EXCEPT:
1. The catalytic constant (k₃ or turnover number) for each isozyme may be different.
2. The chemical composition of each isozyme is the same.
3. The equilibrium constant for the reaction catalyzed by each isozyme is identical.
4. They may be modified post-translationally to different extents in different tissues.
5. They may contain a mixture of subunits coded by different genes.
67. Which of the following mechanisms for regulating enzyme activity is irreversible?
1. Allosteric (binding) interaction of intermediary metabolites.
2. Cleavage of a peptide bond.
3. Phosphorylation of serine residues.
4. Protein-protein interaction.
68. Defects (mutations) in which of the following proteins are most likely to produce classic hemophilia?
1. Factor VIII
2. Factor XI
3. Fibrinogen
4. Protein C
5. Prothrombin

Use the following list of vitamins to answer questions 68 and 69.

 

A. Biotin

B. Cobalamin (Vitamin B₁₂)

C. Folic Acid

D. Thiamin

E. Vitamin K

69. Dicoumarol or warfarin antagonizes its action.
70. Which one functions as a coenzyme primarily involved in the catalytic modification of an amino acid residue in preformed proteins?
71. Which class of enzymes catalyzes the formation of carbon-carbon bonds with the expenditure of energy generally in the form of ATP?
1. Hydrolases
2. Isomerases
3. Ligases
4. Lyases
5. Transferases
72. Serine proteases such as chymotrypsin and trypsin enhance reaction rates by mechanisms that involve
1. acid-base catalysis only.
2. approximation and orientation of substrates.
3. covalent catalysis only.
4. covalent and acid-base catalysis.
5. strain and distortion.
73. An enzyme-catalyzed reaction in the presence of a reversible competitive inhibitor shows which of the following properties?
1. The rate of the reaction approaches Vmax as [S] approaches infinity.
2. The rate of the reaction is unchanged by an increase in [S] concentration.
3. The rate of the reaction continues to decrease in the presence of substrate but at a slower rate as [S] increases.
4. The rate of the reaction continues to decrease and is unchanged by an increase in [S].
74. Zymogens involved in blood coagulation are activated by proteolytic cleavage of specific peptide bonds. The activity of activated hydrolases in blood is stopped by
1. their interaction with specific inhibitors circulating in blood.
2. complete hydrolysis during their circulation in blood.
3. removal in their active enzyme forms by the liver.
4. resynthesis of the cleaved peptide bond to regenerate the zymogen.
75. The active site of enzymes may be characterized by each of the following properties EXCEPT they
1. are clefts or crevices.
2. are formed by amino acids adjacent to each other in the primary sequence.
3. are three dimensional entities.
4. bind substrates by relatively weak forces.
5. occupy a relatively small portion of the molecule.

Choose from the following options to answer questions 75 and 76.

A. Biotin

B. Folic acid

C. Pantothenic acid

D. Pyridoxine

E. Thiamin

76. A component of coenzyme A.
77. Functions in carboxylation reactions.

Choose from the following options to answer questions 77 and 78.

A. Active center

B. Apoenzyme

C. Holoenzyme

D. Molecular activity

E. Specific activity

78. Units of activity per unit weight (mg) of protein.
79. Moles of substrate transformed per unit time per mole of enzyme.