Chapter 14 Test Bank
Chapter 14 Test Bank
Chapter 14 Test Bank
A) aerobic metabolism.
B) anabolic metabolism.
C) a net reductive process.
D) fermentation.
E) oxidative phosphorylation.
2. Glycolysis
Page: 523 Difficulty: 1 Ans: C
The anaerobic conversion of 1 mol of glucose to 2 mol of lactate by fermentation is accompanied by a
net gain of:
A) 1 mol of ATP.
B) 1 mol of NADH.
C) 2 mol of ATP.
D) 2 mol of NADH.
E) none of the above.
5. Glycolysis
Page: 524 Difficulty: 2 Ans: E
The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway
results in a net formation of:
7. Glycolysis
Page: 525 Difficulty: 2 Ans: B
Which of the following statements is not true concerning glycolysis in anaerobic muscle?
8. Glycolysis
Page: 525 Difficulty: 2 Ans: E
When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts
anaerobically because:
9. Glycolysis
Page: 525 Difficulty: 1 Ans: E
Glycolysis in the erythrocyte produces pyruvate that is further metabolized to:
A) CO2.
B) ethanol.
C) glucose.
D) hemoglobin.
E) lactate.
10. Glycolysis
Page: 526 Difficulty: 2 Ans: A
When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme
phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose
6-phosphate. Which one of the following statements is most nearly correct, when applied to the
reaction below (R = 8.315 J/mol·K and T = 298 K)?
11. Glycolysis
Page: 528 Difficulty: 2 Ans: D
In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy
change (∆G'°) of 23.8 kJ/mol. Under what conditions (encountered in a normal cell) will the free-
energy change (∆G) be negative, enabling the reaction to proceed to the right?
A) If the concentrations of the two products are high relative to that of fructose 1,6-bisphosphate.
B) The reaction will not go to the right spontaneously under any conditions because the ∆G'° is
positive.
C) Under standard conditions, enough energy is released to drive the reaction to the right.
D) When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of
products.
E) When there is a high concentration of products relative to the concentration of fructose 1,6-
bisphosphate.
12. Glycolysis
Page: 529 Difficulty: 3 Ans: E
Glucose labeled with 14C in C-1 and C-6 gives rise in glycolysis to pyruvate labeled in:
A) A and C.
B) all three carbons.
C) its carbonyl carbon.
D) its carboxyl carbon.
E) its methyl carbon.
13. Glycolysis
Page: 529 Difficulty: 2 Ans: E
If glucose labeled with 14C at C-1 (the aldehyde carbon) were metabolized in the liver, the first
radioactive pyruvate formed would be labeled in:
A) ADP
B) ATP
C) FAD/FADH2
D) Glyceraldehyde 3-phosphate
E) NAD+/NADH
18. Glycolysis
Pages: 529-531 Difficulty: 2 Ans: C
The steps of glycolysis between glyceraldehyde 3-phosphate and 3-phosphoglycerate involve all of
the following except:
A) ATP synthesis.
B) catalysis by phosphoglycerate kinase.
C) oxidation of NADH to NAD+.
D) the formation of 1,3-bisphosphoglycerate.
E) utilization of Pi.
19. Glycolysis
Page: 530 Difficulty: 2 Ans: A
The first reaction in glycolysis that results in the formation of an energy-rich compound (i.e., a
compound whose hydrolysis has a highly negative ∆G'°) is catalyzed by:
20. Glycolysis
Page: 530 Difficulty: 1 Ans: D
Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate
dehydrogenase?
A) ATP
2+
B) Cu
C) heme
+
D) NAD
+
E) NADP
21. Glycolysis
Page: 532 Difficulty: 2 Ans: A
Inorganic fluoride inhibits enolase. In an anaerobic system that is metabolizing glucose as a
substrate, which of the following compounds would you expect to increase in concentration following
the addition of fluoride?
A) 2-phosphoglycerate
B) Glucose
C) Glyoxylate
D) Phosphoenolpyruvate
E) Pyruvate
A) glucokinase.
B) glucose-6-phosphatase
C) glycogen phosphorylase.
D) glycogen synthase.
E) glycogenase.
A) deficiency of galactokinase.
B) deficiency of UDP-glucose.
C) deficiency of UDP-glucose: galactose 1-phosphate uridylyltransferase.
D) excessive ingestion of galactose.
E) inability to digest lactose.
A) Aerobically, oxidative decarboxylation of pyruvate forms acetate that enters the citric acid cycle.
B) In anaerobic muscle, pyruvate is converted to lactate.
C) In yeast growing anaerobically, pyruvate is converted to ethanol.
D) Reduction of pyruvate to lactate regenerates a cofactor essential for glycolysis.
E) Under anaerobic conditions pyruvate does not form because glycolysis does not occur.
A) acetaldehyde.
B) acetate.
C) ethanol.
D) NAD+.
E) pyruvate.
A) aldolase.
B) hexokinase.
C) lactate dehydrogenase.
D) pyruvate decarboxylase.
E) transaldolase.
27. Gluconeogenesis
Page: 543 Difficulty: 2 Ans: A
Which of the following compounds cannot serve as the starting material for the synthesis of glucose
via gluconeogenesis?
A) acetate
B) glycerol
C) lactate
D) oxaloacetate
E) α-ketoglutarate
28. Gluconeogenesis
Page: 544 Difficulty: 2 Ans: A
An enzyme used in both glycolysis and gluconeogenesis is:
A) 3-phosphoglycerate kinase.
B) glucose 6-phosphatase.
C) hexokinase.
D) phosphofructokinase-1.
E) pyruvate kinase.
29. Gluconeogenesis
Page: 544 Difficulty: 2 Ans: B
Which one of the following statements about gluconeogenesis is false?
A) For starting materials, it can use carbon skeletons derived from certain amino acids.
B) It consists entirely of the reactions of glycolysis, operating in the reverse direction.
C) It employs the enzyme glucose 6-phosphatase.
D) It is one of the ways that mammals maintain normal blood glucose levels between meals.
E) It requires metabolic energy (ATP or GTP).
30. Gluconeogenesis
Page: 547 Difficulty: 2 Ans: D
All of the following enzymes involved in the flow of carbon from glucose to lactate (glycolysis) are
also involved in the reversal of this flow (gluconeogenesis) except:
A) 3-phosphoglycerate kinase.
B) aldolase.
C) enolase.
D) phosphofructokinase-1.
E) phosphoglucoisomerase.
31. Gluconeogenesis
Page: 548 Difficulty: 2 Ans: A
In humans, gluconeogenesis:
32. Gluconeogenesis
Page: 548 Difficulty: 2 Ans: C
Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver?
A) alanine
B) glutamate
C) palmitate
D) pyruvate
E) α-ketoglutarate
A) 6-phosphogluconate dehydrogenase
B) Aldolase
C) Glycogen phosphorylase
D) Phosphofructokinase-1
E) Pyruvate kinase
A) C-1.
B) C-3.
C) C-4.
D) C-5.
E) C-6.
A) carbon dioxide.
B) glycogen.
C) phosphoglycerate.
D) pyruvate.
E) ribulose 5-phosphate.
having a genetic disease in which one of the enzymes of glycolysis is severely affected. Why do you
suppose such mutations are seen so rarely?
Ans: The glycolytic pathway is so central to all of cellular metabolism that mutations in glycolytic
enzymes are lethal; embryos with such mutations would not survive.
43. Glycolysis
Page: 522 Difficulty: 2 Ans: C
Define “fermentation” and explain, by describing relevant reactions, how it differs from glycolysis.
Your explanation should include a discussion of the role of NADH in the reaction(s).
Ans: Fermentation is the operation of the glycolytic pathway under anaerobic conditions. Under
aerobic conditions, the pyruvate produced by glycolysis is oxidized to acetyl-CoA, which passes
through the citric acid cycle. NADH produced in the oxidations passes electrons to O2, and is thus
recycled to NAD+ allowing the continuation of the glycolytic reactions. When no O2 is available to
reoxidize the NADH produced by the glyceraldehyde 3-phosphate dehydrogenase reaction, electrons
from NADH must be passed to one of the products of glycolysis, such as pyruvate or acetaldehyde,
forming lactate or ethanol.
44. Glycolysis
Page: 523 Difficulty: 1 Ans: C
In glycolysis there are two reactions that require one ATP each and two reactions that produce one
ATP each. This being the case, how can fermentation of glucose to lactate lead to the net production
of two ATP molecules per glucose?
Ans: The two reactions that produce ATP in glycolysis (those catalyzed by phosphoglycerate kinase
and pyruvate kinase) involve three-carbon compounds, whereas the two reactions that consume ATP
occur at the level of hexoses. In glycolysis, each hexose yields two trioses, each of which undergoes
the reactions that yield ATP. The ATP yield for triose reactions therefore must be doubled for
stoichiometric comparison with the ATPs consumed in hexose phosphorylation. Two ATP molecules
are consumed and four are produced for each glucose that passes through the pathway, resulting in a
net yield of two ATP per glucose.
45. Glycolysis
Page: 523 Difficulty: 2 Ans: C
Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans, and
explain the circumstances that favor each.
Ans: Under aerobic conditions, pyruvate is oxidized to acetyl-CoA and passes through the citric acid
cycle. Under anaerobic conditions, pyruvate is reduced to lactate to recycle NADH to NAD+,
allowing the continuation of glycolysis.
46. Glycolysis
Page: 523 Difficulty: 2
Show how NADH is recycled to NAD+ under aerobic conditions and under anaerobic conditions.
Why is it important to recycle NADH produced during glycolysis to NAD+?
Ans: Cells contain a limited supply of NAD+ and NADH. The oxidation of glyceraldehyde 3-
phosphate requires NAD+ as as electron acceptor—it converts NAD+ to NADH. Unless this NADH
is recycled to NAD+, oxidative metabolism in this cell will cease for lack of an electron acceptor.
Under aerobic conditions, NADH passes electrons to O2; under anaerobic conditions, NADH reduces
Ans: During vigorous exercise, the cardiovascular system cannot deliver O2 to the muscle tissue fast
enough to maintain aerobic conditions. As glycolysis proceeds under anaerobic conditions, NAD+ is
converted to NADH (during the glyceraldehyde 3-phosphate dehydrogenase reaction), but the muscle
tissue has no O2 to which NADH can pass electrons. To recycle NADH to NAD+, which is essential
for continuing glycolysis, electrons from NADH are used to reduce pyruvate to lactate.
Ans: (a) At rest, plenty of O2 is being delivered to the muscle, and pyruvate formed during glycolysis
is oxidized to acetyl-CoA by the pyruvate dehydrogenase complex. Acetyl groups then enter the
citric acid cycle and are oxidized to CO2 (b) Under the conditions of all-out exertion, skeletal muscle
cannot be supplied with enough O2 to keep metabolism completely aerobic; under these conditions,
muscle tissue must function anaerobically. Pyruvate is reduced to lactate to recycle NADH, formed
by glycolysis, to NAD+, so that glycolysis can continue.
Ans: Lactate dehydrogenase allows cells to pass electrons from NADH to pyruvate, thus regenerating
NAD+ for continued glycolysis under anaerobic conditions. The lack of this enzyme would cause no
significant problems at rest because aerobic red muscle tissue would function well. During strenuous
exercise, however, the absence of lactate dehydrogenase would severely reduce the ability of muscle
to perform anaerobically.
50. Glycolysis
Page: 524 Difficulty: 2
There are two reactions in glycolysis in which an aldose is isomerized to a ketose. For one of these
reactions draw the structures of the aldose and the ketose. For both reactions the ∆G'° is positive.
Briefly explain how the reactions are able to proceed without the input of additional energy.
Ans: The two reactions are those catalyzed by phosphohexose isomerase and triose phosphate
isomerase:
Although both of these reactions have standard free-energy changes (∆G'°) that are positive, they can
occur within cells because the products are immediately removed by the next step in the pathway.
The result is a very low steady-state concentration of the products, making the actual free-energy
changes (∆G) negative:
∆G = ∆G'° + RT ln ([products]/[substrates])
51. Glycolysis
Page: 524 Difficulty: 3
Describe the part of the glycolytic pathway from fructose 6-phosphate to glyceraldehyde 3-phosphate.
Show structures of intermediates, enzyme names, and indicate where any cofactors participate.
Ans: This part of the pathway involves the reactions catalyzed by phosphofructokinase-1, aldolase,
and triose phosphate isomerase. (See the figures from pp. 533-534.)
52. Glycolysis
Page: 524 Difficulty: 2
Describe the glycolytic pathway from fructose 1,6-bisphosphate to 1,3-bisphospho-glycerate,
showing structures of intermediates and names of enzymes. Indicate where any cofactors participate.
Ans: The answer should show the reactions catalyzed by aldolase, triose phosphate isomerase, and
glyceraldehyde 3-phosphate dehydrogenase. (See figures from pp. 533-536.)
A. Lactate
B. Acetaldehyde
C. Acetyl-CoA
D. FAD
E. Glucose 6-phosphate
F. Fructose 1-phosphate
G. Pyruvate
H. Lipoic acid
I. Thiamine pyrophosphate
J. Dihydroxyacetone phosphate
Ans: B, G, I, J
Ans: G; P; G + P; G; G
55. Glycolysis
Page: 526 Difficulty: 2
In the conversion of glucose to pyruvate via glycolysis, all of the following enzymes participate.
Indicate the order in which they function by numbering them.
1 hexokinase
_4__ triose phosphate isomerase
_2__ phosphohexose isomerase
_6__ enolase
_5__ glyceraldehyde 3-phosphate dehydrogenase
_7__ pyruvate kinase
_3__ phosphofructokinase-1
56. Glycolysis
Page: 526 Difficulty: 2 Ans: C
The conversion of glucose into glucose 6-phosphate, which must occur in the breakdown of glucose,
is thermodynamically unfavorable (endergonic). How do cells overcome this problem?
Ans: Cells often drive a thermodynamically unfavorable reaction in the forward direction by coupling
it to a highly exergonic reaction through a common intermediate. In this example, to make glucose 6-
phosphate formation thermodynamically favorable, cells transfer phosphoryl groups from ATP to
glucose. ATP “hydrolysis” is highly exergonic, making the overall reaction exergonic. (Numerical
solution below not required.)
Glucose + Pi → glucose 6-phosphate + H2O ∆G'° = +13.8 kJ/mol
ATP + H2O → ADP + Pi ∆G'° = –30.5 kJ/mol
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
Sum: ATP + glucose → ADP + glucose 6-phosphate ∆G'° = –16.7 kJ/mol
See p. 498; see also Chapter 14.
57. Glycolysis
Page: 528 Difficulty: 3
The conversion of glyceraldehyde 3-phosphate to dihydroxyacetone phosphate is catalyzed by triose
phosphate isomerase. The standard free-energy change (∆G'°) for this reaction is –7.5 kJ/mol. Draw
the two structures. Define the equilibrium constant for the reaction and calculate it using only the
data given here. Be sure to show your work. (R = 8.315 J/mol·K; T = 298 K)
ln Keq' = ∆G'º
RT
Keq' = 20.6
58. Glycolysis
Page: 529 Difficulty: 3
When glucose is oxidized via glycolysis, the carbon atom that bears the phosphate in the 3-
phosphoglycerate formed may have originally been either C-1 or C-6 of the original glucose.
Describe this pathway in just enough detail to explain this fact.
Ans: The 3-phosphoglycerate derived from glucose by glycolysis is formed from glyceraldehyde 3-
phosphate. The action of aldolase on fructose 1,6-bisphosphate produces dihydroxyacetone
phosphate (derived from C-1, C-2, and C-3 of glucose) and glyceraldehyde 3-phosphate (derived
from C-4, C-5, and C-6 of glucose). When triose phosphate isomerase then converts
dihydroxyacetone phosphate to glyceraldehyde 3-phosphate, C-3 of glyceraldehyde 3-phosphate will
contain both C-1 and C-6 from glucose. (See Fig. 15-4, p. 535.)
59. Glycolysis
Page: 529 Difficulty: 3
When glucose labeled with a 14C at C-1 (the aldehyde carbon) passes through glycolysis, the
glyceraldehyde 3-phosphate that is produced from it still contains the radioactive carbon atom. Draw
the structure of glyceraldehyde 3-phosphate, and circle the atom(s) that would be radioactive.
60. Glycolysis
Page: 529 Difficulty: 3
At which point in glycolysis do C-3 and C-4 of glucose become chemically equivalent?
61. Glycolysis
Page: 529 Difficulty: 2
Explain why Pi (inorganic phosphate) is absolutely required for glycolysis to proceed.
Ans: Inorganic phosphate (Pi) is an essential substrate in the reaction catalyzed by glyceraldehyde 3-
phosphate dehydrogenase.
62. Glycolysis
Page: 529 Difficulty: 2
If brewer’s yeast is mixed with pure sugar (glucose) in the absence of phosphate (Pi), no ethanol is
produced. With the addition of a little Pi, ethanol production soon begins. Explain this observation
in 25 words or less.
63. Glycolysis
Page: 530 Difficulty: 2
Draw the structure of 1,3-bisphosphoglycerate. Indicate with an arrow the phosphate ester, and circle
the phosphate group for which the free energy of hydrolysis is very high.
Ans:
64. Glycolysis
Page: 531 Difficulty: 2
Two reactions in glycolysis produce ATP. For each of these, show the name and structure of reactant
and product, indicate which cofactors participate and where, and name the enzymes.
Ans: The two reactions are those catalyzed by phosphoglycerate kinase and pyruvate kinase. (See
reactions on pp. 537 [top] and 539 [bottom].)
Ans: Phosphorolysis yields glucose 1-phosphate, which can be converted into glucose 6-phosphate
without the investment of energy from ATP. Hydrolysis of glycogen yields free glucose, which must
be converted into glucose 6-phosphate (at the expense of ATP) before it can enter glycolysis.
Ans: Muscle glycogen consists of linear polymers of α(1 → 4)-linked D-glucose, with many
branches formed by α(1 → 6) glycosidic linkages to D-glucose. Glycogen phosphorylase in muscle
catalyzes phosphorolytic cleavage of the terminal residue at the nonreducing ends, producing glucose
1-phosphate. When phosphorylase approaches α(1 → 6) branch points, a second enzyme (the
"debranching enzyme") removes the four glucose residues nearest the branch point and reattaches
them in α(1 → 4) linkage at a nonreducing end. Now phosphorylase can continue to degrade the
molecule.
Ans: In lactose intolerance, the enzyme lactase, found in the surface of intestinal epithelial cells in
children, has been lost in adulthood. Without this enzyme, the individual cannot hydrolyze lactose in
the small intestine and take up the resulting monosaccharides; instead, lactose passes into the large
intestine, where it is metabolized by bacteria, producing gastric distress.
68. Gluconeogenesis
Page: 543 Difficulty: 1
What is gluconeogenesis, and what useful purposes does it serve in people?
Ans: Gluconeogenesis is the biosynthesis of glucose from simpler, noncarbohydrate precursors such
as oxaloacetate or pyruvate. During periods of fasting, when carbohydrate reserves have been
exhausted, gluconeogenesis provides glucose for metabolism in tissues (brain, erythrocytes) that
derive their energy primarily from glucose metabolism.
69. Gluconeogenesis
Pages: 544-545 Difficulty: 3
In gluconeogenesis, how do animals convert pyruvate to phosphoenolpyruvate? Show structures,
enzymes, and cofactors.
Ans: Ribose 5-phosphate is produced from glucose by the reactions of the pentose phosphate
pathway. (See Fig. 15-20, p. 558.)
Ans: The pentose phosphate pathway produces pentose phosphates (for nucleotide synthesis) and
NADPH (reducing agent for biosynthetic processes).
Ans: The tissue must be oxidizing glucose primarily by the pentose phosphate pathway, in which C-1
is released (as CO2) earlier than C-6. During glycolysis, C-1 and C-6 become equivalent at the level
of glyceraldehyde 3-phosphate, and C-1 and C-6 are thus released simultaneously (during passage of
acetate through the citric acid cycle).