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MedBiochem Exam 2, 1996
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MedBiochem Exam 2, 1996
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Page 1 of 27
For each of the following questions, choose the one best
answer.
(Answer key at bottom of page.)
Biochemistry
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1. Which of the following is the correct sequence of carriers in the electron
transport chain?
A. NADH/CoQ reductase à cytochrome c à CoQ à cytochrome reductase
cytochrome oxidase
B. CoQ à cytochrome reductase à cytochrome oxidase à cytochrome c
NADH/CoQ reductase
C. NADH/CoQ reductase à cytochrome reductase à cytochrome c à
cytochrome oxidase
D. NADH/CoQ reductase à CoQ à cytochrome c à cytochrome oxidase
cytochrome reductase
E. NADH/CoQ reductase à CoQ à cytochrome reductase à cytochrome c
cytochrome oxidase.
2. Found in the cytoplasm:
A. pyruvate dehydrogenase complex
B. α -ketoglutarate dehydrogenase complex
C. Both
D. Neither
3. Activated by high concentrations of acetyl CoA:
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A. pyruvate dehydrogenase complex
B. α -ketoglutarate dehydrogenase complex
C. Both
D. Neither
4. Glucose 1-phosphate can be converted to fructose 6-phosphate in the
following two reactions. What is the value of ∆ Go’ for the overall conversion?
Glucose 1-phosphate ß à glucose 6-phosphate ∆ Go’ = -1.7 kcal/mol
Glucose 6-phosphate ß à fructose 6-phosphate ∆ Go’ = -0.4 kcal/mol
A. -2.1 kcal/mol
B. -1.3 kcal/mol
C. -0.0 kcal/mol
D. +1.3 kcal/mol
E. +2.1 kcal/mol
5. Which of the following vitamins is a component of coenzyme A (CoA)?
A. riboflavin
B. thiamine
C. biotin
D. pantothenic acid
E. vitamin A
6. Concerning the synthesis of purine nucleotides and its regulation, which of
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the following statements is INCORRECT:
A. GMP inhibits its own synthesis from IMP.
B. AMP inhibits its own synthesis from IMP.
C. GMP and AMP inhibit the formation of IMP from ribose 5-phosphate.
D. PRPP is required for the synthesis of IMP.
E. Orotate is combined with PRPP to form IMP.
7. Which of the following contains an α -1,6- bond?
(A through D are structures for various glycosidic linkages. Correct answer
showed branch point in glycogen.)
8. Which of the following is or contains maltose?
(A through D showed same set of figures as #7. Included sucrose, lactose, and,
of course, maltose.)
9. Which of the following is or contains a pentose?
(A through D showed methyl-ribose, a glycoside, along with glucose, and
fructose containing structures. The methyl-ribose was the correct answer.)
10. Which of the following statements about ketone bodies is INCORRECT?
A. They are formed in liver mitochondria from 3-hydroxy-3-methyl glutaryl
CoA.
B. They are oxidized in the heart in a set of reactions that requires succinyl
CoA.
C. They include acetoacetate and 3-hydroxybutyrate.
D. They give rise to the net synthesis of oxaloacetate in skeletal muscle.
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E. They occur during periods of elevated usage of fatty acids for energy.
11. Which of the following does NOT regulate biochemical reactions?
A. Regulation of enzyme amounts.
B. Regulation of access of substrates to certain compartments.
C. Alteration of ∆ Go’ by raising or lowering reactant concentrations.
D. Regulation of the catalytic activities of enzymes.
E. Alteration of the amounts of allosteric modifiers (regulator molecules).
12. Gluconeogenesis:
A. is favored when insulin concentrations are high.
B. occurs in the liver during muscle activity.
C. allows skeletal muscle to produce glucose for export to the blood for use by
the central nervous system and the brain.
D. is stimulated by high levels of glucose 6-phosphate.
E. uses acetyl CoA as a substrate.
13. The steps in glycolysis between glyceraldehyde 3-phosphate and 3phosphoglycerate involve each of the following EXCEPT:
A. ATP synthesis at the substrate level.
B. the utilization of Pi.
C. the reduction of NAD+ to NADH
D. the formation of 1,3-bisphosphoglycerate.
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E. catalysis by pyruvate kinase.
14. Which enzyme catalyzes the rate limiting step in glycolysis?
A. hexokinase.
B. phosphofructokinase.
C. fructose 1,6-bisphosphatase.
D. pyruvate kinase
E. pyruvate dehydrogenase complex
15. A phosphorylase deficiency:
A. in skeletal muscle leads to excessive amounts of glycogen in the liver.
B. in skeletal muscle leads to inability to perform exercise.
C. in liver leads to storage of glycogen with an unusual branching pattern.
D. in liver is associated with hyperglycemia.
16. Glycerol 3-phosphate for lipid synthesis in adipose tissue is formed in which
of the following reactions?
A. reduction of dihydroxyacetone phosphate
B. phosphorylation of glycerol by glycerol kinase
C. reductive phosphorylation of pyruvate
D. oxidation of glyceraldehyde 3-phosphate
E. dephosphorylation of 1,3-bisphosphoglycerate
17. Bilirubin:
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A. is conjugated with succinyl groups to make it more water soluble.
B. is conjugated with UDP-glucose to aid in its excretion.
C. is formed from biliverdin.
D. is a precursor of heme.
E. is a precursor of porphobilinogen.
18. Fructose 2,6-bisphosphate:
A. is required for gluconeogenesis.
B. synthesis is stimulated by insulin.
C. is formed by the action of fructokinase on fructose 2-phosphate.
D. inhibits PFK.
E. stimulates fructose 1,6-bisphosphatase.
19. The TCA cycle accomplishes each of the following EXCEPT:
A. formation of NADH and FADH2.
B. provision of α -ketoglutarate needed for aminotransferases.
C. provision of oxaloacetate needed for gluconeogenesis.
D. formation of pyruvate from acetyl CoA.
E. formation of GTP.
20. Which of the following statements about Lesch-Nyhan syndrome is
INCORRECT?
A. The disease is caused by a deficiency of hypoxanthine/guanine
phosphoribosyl transferase (HGPRT)
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B. Patients excrete elevated levels of uric acid.
C. Methotrexate treatment overcomes the biochemical defect.
D. Absence of HGPRT leads to excessive purine production.
21. If the ∆ G’ value of the following reaction is -3.0, which of the following
statements is TRUE?
Xß à Y
A. The reaction is irreversible.
B. The ∆ Go’ value can be calculated from the initial concentrations of X and Y.
C. X and Y must be present in equal amounts.
D. The reaction proceeds to the right with the net conversion of X to Y.
E. The reaction is at equilibrium.
22. The rate of glycolysis is increased by
A. insulin.
B. ATP.
C. citrate.
D. NADH.
E. malonyl CoA.
Use the following figure to answer questions 23 and 24 (Figure is unlabeled
TCA cycle with arrows pointing to letters to show reaction products)
23. I am GTP. (identify structure of GTP)
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24. I am FADH2. (identify structure of FADH2)
25. Unsaturated fatty acids:
A. are required in the diet if the double bond is near the carboxyl group.
B. in the diet have double bonds that are nearly always in the trans
configuration.
C. for incorporation into membranes are produced by
fatty acids in the mitochondria.
-oxidation of saturated
D. require the action of cytochrome b5, located outside the mitochondria, for
their synthesis.
E. are produced from saturated fatty acids in a set of reactions that also
produces NADH.
26. Dietary deficiency of which amino acid leads to negative nitrogen balance?
A. aspartic acid
B. glutamic acid
C. alanine
D. phenylalanine
E. All of the above since all amino acids would have to be deficient for negative
balance to occur.
27. Which carrier contains cytochrome a3 and binds to oxygen?
A. cytochrome c
B. cytochrome oxidase
C. cytochrome reductase
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D. cytochrome b5
E. NADH/CoQ reductase
28. Which of the following does NOT contain thiamine pyrophosphate?
A. lactate dehydrogenase
B. transketolase
C. pyruvate dehydrogenase
D. α -ketoglutarate dehydrogenase
E. All of the above contain thiamine pyrophosphate.
29. Aminotransferase reactions require which of the following cofactors?
A. vitamin C
B. pyridoxal phosphate (vitamin B6)
C. biotin (vitamin H)
D. riboflavin (vitamin B2)
E. thiamin (vitamin B1)
30. Which of the following statements about the pentose phosphate pathway is
INCORRECT?
A. Pentoses can be formed both oxidatively and non-oxidatively.
B. This pathway is important to fatty acid synthesis because it produces
reducing equivalents.
C. Fructose 6-phosphate can be used to make ribose 5-phosphate.
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D. Glyceraldehyde 3-phosphate can be used to make ribose 5-phosphate.
E. NADH is formed by the action of glucose 6-phosphate dehydrogenase.
31. Which of the following is the first substance during purine biosynthesis to
have a fully formed purine ring?
A. AMP
B. GMP
C. IMP
D. CMP
E. UMP
32. The synthesis of phosphoenolpyruvate from pyruvate:
A. requires pyruvate kinase.
B. requires the participation of both the cytosol and the mitochondria.
C. is the last step in glycolysis.
D. requires the formation of GTP.
E. never occurs because the pyruvate kinase reaction is irreversible.
33. An anomeric carbon is:
A. always carbon number 1.
B. never attached through a glycosidic bond.
C. always attached to two oxygen atoms when in a sugar is drawn in a ring
structure.
D. never involved in branching.
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E. found in triacylglycerol molecules.
34. Glycogen:
A. phosphorolysis occurs from the reducing end.
B. is less branched than amylose.
C. synthesis is stimulated by insulin.
D. degradation is stimulated by high concentrations of glucose 6-phosphate.
E. degradation requires the branching enzyme.
35. Epinephrine:
A. activates glycogen synthesis in muscle.
B. works via a GMP-dependent protein kinase.
C. stimulates the phosphorylation of pyruvate dehydrogenase.
D. receptors activate glycogen synthesis in the liver more readily than do
glucagon receptors.
E. inhibits (inactivates) the protein phosphatase that dephosphorylates glycogen
synthase.
36. Aerobic glycolysis
A. is characterized by the depletion of acetyl CoA.
B. is associated with accumulation of lactate in the blood stream during
exercise.
C. is favored over anaerobic glycolysis in muscles at rest.
D. does not require the presence of mitochondria.
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E. occurs only in the liver.
37. Which list of fatty acids shows them in order of decreasing melting points.
A. a saturated fatty acid with 20 carbons, stearate, oleate, linoleate, linolenate
B. a saturated fatty acid with 20 carbons, linolenate, linoleate, oleate, stearate
C. oleate, linoleate, linolenate, a saturated fatty acid with 20 carbons, stearate
D. linolenate, linoleate, oleate, a saturated fatty acid with 20 carbons, stearate
E. linolenate, linoleate, oleate, stearate, a saturated fatty acid with 20 carbons
38. Which of the following statements about energy storage is INCORRECT?
A. Triacylglyerols are stored in an anhydrous form.
B. Glycogen is more highly reduced than triacylglycerols.
C. Liver glycogen can be used to produce glucose for the blood.
D. Alanine, aspartic acid and glutamic acid can be converted to glucose.
E. Muscle proteins are broken down to amino acids whose amino groups are
ultimately converted to urea and whose corresponding α -keto acids can be used
for energy.
39. Which of the following vitamins is required in the hydroxylation of
collagen?
A. vitamin A
B. vitamin C
C. vitamin D
D. biotin
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E. vitamin B6 (pyridoxal phosphate)
40. Uncoupling agents like dinitrophenol uncouple ATP synthesis from
respiration by:
A. dissipation of the proton gradient.
B. inhibiting cytochrome reductase.
C. binding to the copper in cytochrome oxidase.
D. dissociating the F1 subunits from the F0 subunits of ATP synthase.
E. blocking ATP/ADP exchange.
41. Which of the following statements about glucose 6-phosphate dehydrogenase
is INCORRECT?
A. It is required for the release of glucose into the blood stream during
gluconeogenesis.
B. It is deficient in red blood cells exhibiting primaquine sensitivity.
C. It is found in the cytoplasm.
D. It is required to maintain glutathione in the reduced form.
E. It catalyzes the first step in the oxidative branch of the pentose phosphate
pathway.
42. Citrate:
A. stimulates glycolysis.
B. inhibits fatty acid synthesis.
C. provides carbon dioxide for incorporation into fatty acids.
D. transports acetyl CoA from the mitochondria to the cytosol for fatty acid
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biosynthesis.
E. transports reducing power from the cytosol to the mitochondria for fatty
acid biosynthesis.
43. Insulin:
A. activates acetyl CoA carboxylase.
B. causes the phosphorylation of acetyl CoA carboxylase.
C. stimulates lipolysis.
D. inhibits the formation of malonyl CoA.
E. inhibits fatty acid synthesis in adipose cells.
44. Which of the following inhibitors binds to and blocks electron flow at
cytochrome reductase?
A. carbon monoxide
B. antimycin a
C. atractyloside
D. oligomycin
E. amytal
45. In aminotransferase reactions, which of the following serves as the acceptor
of nitrogen from amino acids?
A. glutamine
B. glutamic acid
C. α -ketoglutaric acid
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D. oxaloacetic acid
E. aspartic acid
46. Which of the following may NOT serve as a precursor of phosphatidyl
choline or one of its components?
A. CDP-choline
B. phosphatidic acid
C. sphingosine
D. S-adenosyl methionine
E. phosphatidyl ethanolamine
47. Which if the following statements about glutamic acid is INCORRECT?:
A. Glutamic acid is formed during aminotransferase reactions from most amino
acids.
B. Glutamic acid is converted to α -ketoglutaric acid by the action of glutamic
acid dehydrogenase.
C. Glutamic acid is a source of free ammonium ion for urea production.
D. Glutamic acid is a source of amino nitrogen for the synthesis of alanine from
pyruvic acid.
E. Glutamic acid is a source of the amino nitrogen in urea because it reacts with
citrulline to form arginoglutamic acid.
48. _____________ high energy phosphate linkages are utilized and
_____________ high energy phosphate linkages are formed at the substrate
level in glycolysis of one glucose molecule.
A. 2, 0
B. 2, 2
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C. 2, 4
D. 4, 2
E. 0, 2
49. Which of the following is NOT a precursor of cholesterol?
A. malonyl CoA
B. mevalonic acid
C. 3-hydroxy-3-methylglutaryl CoA
D. isoprene units
E. squalene
50. Urea is formed:
A. in liver mitochondria.
B. in skeletal muscle where excess amino acids are stored and metabolized.
C. by hydrolysis of the ureido group of the amino acid histidine.
D. by uricotelic animals.
E. only on Friday.
51. Chronic alcohol consumption:
A. leads to decreased NADH production in the cytosol and mitochondria.
B. leads to hyperglycemia because alcohol is converted to glucose at a high rate.
C. leads to increased rates of inactivation of certain drugs in the alcohol
state.
D. leads to decreased smooth endoplasmic reticulum production in the liver.
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E. leads to decreased chylomicron production by the liver.
52. Which of the following statements about CoQ (ubiquinol) is INCORRCT?
A. It is localized to the inner mitochondrial membrane.
B. It is a mobile carrier between cytochrome reductase and cytochrome oxidase.
C. It is reversibly oxidized and reduced during electron transport.
D. It is a lipid-soluble molecule.
E. The oxidized form is reduced by NADH/CoQ reductase and the reduced
form is oxidized by cytochrome reductase.
53. Which amino acid donates a one-carbon unit carried on tetrahydrofolic
acid?
A. glycine
B. serine
C. phenylalanine
D. leucine
E. lysine
54. Each of the following cofactors is required in the action of α -ketoglutarate
dehydrogenase EXCEPT which one?
A. lipoic acid
B. thiamine pyrophosphate
C. biotin
D. NAD+
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E. FAD
55. How many steps in the oxidation of acetyl CoA in one complete cycle of the
TCA cycle yield a pair of reducing equivalents?
A. 1
B. 2
C. 3
D. 4
E. 5
56. Place the following reactions and locations in the correct sequence in fatty
acid oxidation.
a. hydration
b. thiolysis
c. FAD-linked oxidation
d. fatty acid in cytosol
e. fatty acyl CoA in mitochondrion
f. NAD-linked oxidation
g. activation of fatty acid by joining to CoA
h. reaction with carnitine
A. e, h, g, a, f, c, b, d
B. b, a, h, c, e, f, g, d
C. d, g, h, e, c, a, f, b
D. d, g, h, e, f, a, c, b
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E. d, e, h, g, a, c, f, b
57. All of the following provide atoms for purine synthesis EXCEPT which one?
A. aspartate
B. glutamine
C. glycine
D. N10-formyl tetrahydrofolic acid
E. succinyl CoA
58. Which of the following statements about glucokinase is TRUE?
A. Glucokinase has a higher affinity for glucose than hexokinase.
B. Glucokinase is found in the brain.
C. Glucokinase is the major enzyme in the liver responsible for the
phosphorylation of glucose.
D. Glucokinase is inhibited by glucose 6-phosphate.
E. Glucagon stimulates the production of glucokinase.
59. Pyruvate carboxylase:
A. requires acetyl CoA for activity.
B. occurs in the cytosol.
C. catalyzes an irreversible reaction in glycolysis.
D. catalyzes the first step in fatty acid synthesis.
E. produces carbon dioxide.
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60. Which of the following statements about the coupling of reactions is NOT
true?
A. Reactions that share a common intermediate are coupled.
B. When reactions are coupled, some reactions may be exergonic.
C. Reactions can be coupled by way of an ionic gradient across a membrane.
D. Reactions can be coupled if the product of one reaction is the reactant of
another reaction.
E. For reactions to be coupled all of the reactions must have ∆ Go’ values that
are negative.
For each of the following questions, one or more of the answers are correct.
Choose answer:
A. If only 1, 2, and 3 are correct.
B. If only 1 and 3 are correct.
C. If only 2 and 4 are correct.
D. If only 4 is correct.
E. If all are correct.
61. The complete utilization of lactose in the diet for glycogen synthesis in
normal adults requires:
1. galactokinase.
2. lactase.
3. UDP-glucose.
4. an epimerase.
62. Precursors of heme.
1. succinyl CoA
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2. δ -aminolevulinic acid
3. glycine
4. porphobilinogen
63. Reactions occurring in the mitochondria include:
1. pentose phosphate pathway.
2. pyruvate carboxylation.
3. fatty acid synthesis.
4. fatty acid oxidation.
64. In the glycerol 3-phosphate shuttle,
1. electrons are shuttled into the mitochondria and enter the electron transport
chain at NADH/CoQ reductase.
2. dihydroxyacetone phosphate is formed in the mitochondria.
3. NADH is formed.
4. regenerates NAD+ for use in glycolysis.
65. Which of the following is/are consistent with the chemiosmotic mechanism
of ATP production in mitochondria?
1. An intact mitochondrial membrane is required for ATP synthesis.
2. A proton gradient is formed across the inner membrane during electron
transport.
3. A proton gradient is dissipated during ATP synthesis.
4. The carriers of electrons and the ATP synthase are symmetrically distributed
across the inner membrane.
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66. Carbamoyl phosphate synthetase:
1. is found in the mitochondria.
2. is found in the cytosol.
3. is required for pyrimidine biosynthesis.
4. is required for urea synthesis.
67. In which organs is the pentose phosphate pathway active?
1. liver
2. red blood cells
3. adipose tissue
4. skeletal muscle
68. A patient with glucose 6-phosphatase deficiency:
1. would experience hypoglycemia during fasting.
2. would not experience hypoglycemia because free glucose in the blood can be
derived from gluconeogenesis.
3. has elevated amounts of liver glycogen.
4. could use fructose as an alternative source of blood glucose.
69. NADPH:
1. is formed upon the conversion of malate to pyruvate in the cytosol.
2. is used mostly in reductive biosyntheses.
3. is formed from glucose 6-phosphate in the cytosol.
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4. is oxidized in mitochondria by passing its electrons on to NADH/CoQ
reductase in the electron transport chain.
70. Identify the high energy molecule(s).
1. glycerol 3-phosphate
2. glyceraldehyde 3-phosphate
3. 3-phosphoglycerate
4. phosphoenolpyruvate
71. Which of the following enzymes catalyze(s) a physiologically reversible
reaction.
1. phosphofructokinase
2. pyruvate dehydrogenase complex
3. pyruvate kinase
4. malate dehydrogenase
72. Amino acids in the diet may be converted into:
1. proteins.
2. fatty acids.
3. ketone bodies.
4. glucose.
CHOOSE THE SINGLE MOST APPROPRIATE ANSWER
73. Heavy meromyosin
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A. contains the portion of the myosin molecule that delivers the power stroke in
muscle
contraction.
B. is the tail portion of the myosin molecule.
C. interacts with monomeric G-actin during muscle contraction.
D. contains no enzymatic activity.
E. consists of two peptides.
74. During normal contraction of mammalian striated muscle, the
A. A band shortens with no change in the length of the I band.
B. I band shortens with no change in the length of the A band.
C. I band and A band shorten simultaneously.
D. the thick filaments shorten with no change in the length of thin filaments.
E. the thin filaments shorten with no change in the thick filaments.
75. Which thin filament protein is composed of three non-identical subunits?
A. Troponin
B. F-Actin
C. G-Actin
D. Tropomyosin
76. The sensitivity of the myofibril to calcium ions is most directly related to
A. myosin.
B. tropomyosin.
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C. troponin.
D. actin.
E. actinin.
77. A protein finds its most stable conformation by random sampling of all
possible conformations.
A. True
B. False
78. Which of the following treatments would NOT be expected to result in
unfolding of a typical protein.
A. increase in temperature to 70oC.
B. addition of guanidine hydrochloride to a 5 M concentration
C. decrease of pH from 7 to 2
D. reduction of urea concentration from 7 M to 0.1 M
E. treatment with
-mercaptoethanol and urea
79. Which of the statements about protein disulfide isomerase is INCORRECT
A. It accelerates disulfide interchange during protein folding.
B. It contains cys residues in its active site.
C. It catalyzes the cis-trans isomerization of peptide bonds adjacent to cys
residues.
D. It forms a disulfide bond with the substrate during catalysis.
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80. Which of the following is true?
A.The cis-trans configuration of the peptide bonds of a protein is unimportant
in protein folding.
B. The peptide bonds in proteins are rarely in the trans configuration.
C. Cis-trans transitions for X-pro peptide bonds are much more rapid than for
other peptide bonds.
D. Peptidyl prolyl cis-trans isomerase accelerates cis→ trans transitions but not
trans→ cis transitions.
E. In native proteins, X-pro bonds frequently are found in the cis configuration.
1. E
11. C
21. D
31. C
41. A
51. C
61. E
2. D
12. B
22. A
32. B
42. D
52. B
62. E
3. D
13. E
23. C
33. C
43. A
53. B
63. C
4. A
14. B
24. D
34. C
44. B
54. C
64. D
5. D
15. B
25. D
35. E
45. C
55. D
65. A
6. E
16. A
26. D
36. C
46. C
56. C
66. E
7. C
17. C
27. B
37. A
47. E
57. E
67. A
8. D
18. B
28. A
38. B
48. C
58. C
68. B
9. A
19. D
29. B
39. B
49. A
59. A
69. A
10. D
20. C
30. E
40. A
50. A
60. E
70. D
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Copyright © 1998 Department of Cell Biology & Biochemistry, TTUHSC
Last revised 11/30/99
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