Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose
Phosphate Pathway
Multiple Choice Questions
1. Glycolysis
Glycolysis is the name given to a metabolic pathway occurring in many different cell types. It
consists of 11 enzymatic steps that convert glucose to lactic acid. Glycolysis is an example of:
A) aerobic metabolism.
B) anabolic metabolism.
C) a net reductive process.
D) fermentation.
E) oxidative phosphorylation.
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:
A) 1 mol of NAD+ and 2 mol of ATP.
B) 1 mol of NADH and 1 mol of ATP.
C) 2 mol of NAD+ and 4 mol of ATP.
D) 2 mol of NADH and 2 mol of ATP.
E) 2 mol of NADH and 4 mol of ATP.
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)?
Glucose 6-phosphate ↔ fructose 6-phosphate
A) G'° is +1.7 kJ/mol.
B) G'° is –1.7 kJ/mol.
C) G'° is incalculably large and negative.
D) G'° is incalculably large and positive.
E) G'° is zero.
4. Glycolysis
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?
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
158
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.
5. Glycolysis
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.
6. Glycolysis
If glucose labeled with 14C at C-2 were metabolized in the liver, the first radioactive pyruvate formed
would be labeled in:
A) all three carbons.
B) both A and C.
C) its carbonyl carbon.
D) its carboxyl carbon.
E) its methyl carbon.
Which of the following reactions in glycolysis requires ATP as a substrate?
A) Hexokinase
B) Glyceraldehyde-3-phosphate dehydrogenase
C) Pyruvate kinase
D) Aldolase
E) Phosphoglycerate kinase
8. Glycolysis
Which of the following reactions in glycolysis produces ATP as a product?
A) Hexokinase
B) Glyceraldehyde-3-phosphate dehydrogenase
C) Pyruvate kinase
D) Aldolase
E) Phosphofructokinase-1
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
159
Which of the following reactions in glycolysis is an aldose to ketose isomerization?
A) Enolase
B) Phosphoglycerate mutase
C) Phosphohexose isomerase
D) Aldolase
E) Glyceraldehyde-3-phosphate dehydrogenase
Which of the following reactions in glycolysis is a ketose to aldose isomerization?
A) Hexokinase
B) Phosphoglycerate mutase
C) Enolase
D) Aldolase
E) Triose phosphate isomerase
11. Glycolysis
Which of the following reactions in glycolysis utilizes a covalent enzyme intermediate?
A) Phosphofructokinase-1
B) Hexokinase
C) Phosphohexose isomerase
D) Aldolase
E) Triose phosphate isomerase
12. Glycolysis
Which of the following reactions in glycolysis utilizes a covalent enzyme intermediate?
A) Phosphofructokinase-1
B) Glyceraldehyde-3-phosphate dehydrogenase
C) Phosphohexose isomerase
D) Enolase
E) Triose phosphate isomerase
13. Glycolysis
The compound [18F]2-fluoro-2-deoxyglucose is:
A) an intermediate in glycolysis
B) a positive regulator of glycolysis
C) a potent anti-cancer agent
D) an antibiotic
E) an imaging agent used to detect tumors
14. Glycolysis
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
160
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.
15. Glycolysis
The first reaction in glycolysis that results in the formation of an energy-rich compound is catalyzed
by:
A) glyceraldehyde 3-phosphate dehydrogenase.
B) hexokinase.
C) phosphofructokinase-1.
D) phosphoglycerate kinase.
E) triose phosphate isomerase.
16. Glycolysis
Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate
dehydrogenase?
A) ATP
B) Cu2+
C) heme
D) NAD+
E) NADP+
17. Glycolysis
In the phosphoglycerate mutase reaction, the side chain of which amino acid in the enzyme is
transiently phosphorylated as part of the reaction?
A) Serine
B) Threonine
C) Tyrosine
D) Histidine
E) Arginine
18. Glycolysis
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
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
161
B) Glucose
C) Glyoxylate
D) Phosphoenolpyruvate
E) Pyruvate
19. Feeder pathways for glycolysis
Glycogen is converted to monosaccharide units by:
A) glucokinase.
B) glucose-6-phosphatase
C) glycogen phosphorylase.
D) glycogen synthase.
E) glycogenase.
20. Feeder pathways for glycolysis
Galactosemia is a genetic error of metabolism associated with:
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.
21. Fates of pyruvate under anaerobic conditions: fermentation
During strenuous exercise, the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase
reaction in skeletal muscle must be reoxidized to NAD+ if glycolysis is to continue. The most
important reaction involved in the reoxidation of NADH is:
A) dihydroxyacetone phosphate → glycerol 3-phosphate.
B) glucose 6-phosphate → fructose 6-phosphate.
C) isocitrate →
-ketoglutarate.
D) oxaloacetate → malate.
E) pyruvate → lactate.
22. Fates of pyruvate under anaerobic conditions: fermentation
In an anaerobic muscle preparation, lactate formed from glucose labeled in C-3 and C-4 would be
labeled in:
A) all three carbon atoms.
B) only the carbon atom carrying the OH.
C) only the carboxyl carbon atom.
D) only the methyl carbon atom.
E) the methyl and carboxyl carbon atoms.
23. Fates of pyruvate under anaerobic conditions: fermentation
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
162
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
24. Fates of pyruvate under anaerobic conditions: fermentation
If glucose labeled with 14C in C-1 were fed to yeast carrying out the ethanol fermentation, where
would the 14C label be in the products?
A) In C-1 of ethanol and CO2
B) In C-1 of ethanol only
C) In C-2 (methyl group) of ethanol only
D) In C-2 of ethanol and CO2
E) In CO2 only
25. Fates of pyruvate under anaerobic conditions: fermentation
In an anaerobic muscle preparation, lactate formed from glucose labeled in C-2 would be labeled in:
A) all three carbon atoms.
B) only the carbon atom carrying the OH.
C) only the carboxyl carbon atom.
D) only the methyl carbon atom.
E) the methyl and carboxyl carbon atoms.
26. Fates of pyruvate under anaerobic conditions: fermentation
Which of these cofactors participates directly in most of the oxidation-reduction reactions in the
fermentation of glucose to lactate?
A) ADP
B) ATP
C) FAD/FADH2
D) Glyceraldehyde 3-phosphate
E) NAD+/NADH
27. Fates of pyruvate under anaerobic conditions: fermentation
In comparison with the resting state, actively contracting human muscle tissue has a:
A) higher concentration of ATP.
B) higher rate of lactate formation.
C) lower consumption of glucose.
D) lower rate of consumption of oxygen
E) lower ratio of NADH to NAD+.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
163
28. Fates of pyruvate under anaerobic conditions: fermentation
Which of the following statements is not true concerning glycolysis in anaerobic muscle?
A) Fructose 1,6-bisphosphatase is one of the enzymes of the pathway.
B) It is an endergonic process.
C) It results in net synthesis of ATP.
D) It results in synthesis of NADH.
E) Its rate is slowed by a high [ATP]/[ADP] ratio.
29. Fates of pyruvate under anaerobic conditions: fermentation
When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts
anaerobically because:
A) glycolysis does not occur to significant extent under aerobic conditions.
B) muscle is metabolically less active under aerobic than anaerobic conditions.
C) the lactic acid generated is rapidly incorporated into lipids under aerobic conditions.
D) under aerobic conditions in muscle, the major energy-yielding pathway is the pentose phosphate
pathway, which does not produce lactate.
E) under aerobic conditions most of the pyruvate generated as a result of glycolysis is oxidized by
the citric acid cycle rather than reduced to lactate.
Which of the following statements is incorrect?
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.
31. Fates of pyruvate under anaerobic conditions: fermentation
The ultimate electron acceptor in the fermentation of glucose to ethanol is:
A) acetaldehyde.
B) acetate.
C) ethanol.
D) NAD+.
E) pyruvate.
32. Fates of pyruvate under anaerobic conditions: fermentation
In the alcoholic fermentation of glucose by yeast, thiamine pyrophosphate is a coenzyme required by:
A) aldolase.
B) hexokinase.
C) lactate dehydrogenase.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
164
D) pyruvate decarboxylase.
E) transaldolase.
33. Gluconeogenesis
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)
-ketoglutarate
34. Gluconeogenesis
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.
35. Gluconeogenesis
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).
36. Gluconeogenesis
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.
37. Gluconeogenesis
In humans, gluconeogenesis:
A) can result in the conversion of protein into blood glucose.
B) helps to reduce blood glucose after a carbohydrate-rich meal.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
165
C) is activated by the hormone insulin
D) is essential in the conversion of fatty acids to glucose.
E) requires the enzyme hexokinase.
38. Gluconeogenesis
Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver?
A) Alanine
B) Glutamate
C) Palmitate
D) Pyruvate
E)
-ketoglutarate
39. The pentose phosphate pathway of glucose oxidation
Which of the following statements about the pentose phosphate pathway is correct?
A) It generates 36 mol of ATP per mole of glucose consumed.
B) It generates 6 moles of CO2 for each mole of glucose consumed
C) It is a reductive pathway; it consumes NADH.
D) It is present in plants, but not in animals.
E) It provides precursors for the synthesis of nucleotides.
40. The pentose phosphate pathway of glucose oxidation
The metabolic function of the pentose phosphate pathway is to:
A) act as a source of ADP biosynthesis.
B) generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids.
C) participate in oxidation-reduction reactions during the formation of H2O.
D) provide intermediates for the citric acid cycle.
E) synthesize phosphorus pentoxide.
41. The pentose phosphate pathway of glucose oxidation
Which of the following statements about the pentose phosphate pathway is incorrect?
A) It generates CO2 from C-1 of glucose.
B) It involves the conversion of an aldohexose to an aldopentose.
C) It is prominant in lactating mammary gland.
D) It is principally directed toward the generation of NADPH.
E) It requires the participation of molecular oxygen.
42. The pentose phosphate pathway of glucose oxidation
Glucose breakdown in certain mammalian and bacterial cells can occur by mechanisms other than
classic glycolysis. In most of these, glucose 6-phosphate is oxidized to 6-phosphogluconate, which is
then further metabolized by:
A) an aldolase-type split to form glyceric acid and glyceraldehyde 3-phosphate.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
166
B) an aldolase-type split to form glycolic acid and erythrose 4-phosphate.
C) conversion to 1,6-bisphosphogluconate.
D) decarboxylation to produce keto- and aldopentoses.
E) oxidation to a six-carbon dicarboxylic acid.
43. The pentose phosphate pathway of glucose oxidation
Which of the following enzymes acts in the pentose phosphate pathway?
A) 6-Phosphogluconate dehydrogenase
B) Aldolase
C) Glycogen phosphorylase
D) Phosphofructokinase-1
E) Pyruvate kinase
44. The pentose phosphate pathway of glucose oxidation
The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of:
A) 2 mol of pentose, 4 mol of NADPH, and 8 mol of CO2.
B) 3 mol of pentose, 4 mol of NADPH, and 3 mol of CO2.
C) 3 mol of pentose, 6 mol of NADPH, and 3 mol of CO2.
D) 4 mol of pentose, 3 mol of NADPH, and 3 mol of CO2.
E) 4 mol of pentose, 6 mol of NADPH, and 6 mol of CO2.
45. The pentose phosphate pathway of glucose oxidation
Glucose, labeled with 14C in different carbon atoms, is added to a crude extract of a tissue rich in the
enzymes of the pentose phosphate pathway. The most rapid production of 14CO2 will occur when the
glucose is labeled in:
A) C-1.
B) C-3.
C) C-4.
D) C-5.
E) C-6.
46. The pentose phosphate pathway of glucose oxidation
In a tissue that metabolizes glucose via the pentose phosphate pathway, C-1 of glucose would be
expected to end up principally in:
A) carbon dioxide.
B) glycogen.
C) phosphoglycerate.
D) pyruvate.
E) ribulose 5-phosphate.
Short Answer Questions
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
167
47. Glycolysis
Page: 544 Difficulty: 2
There are a variety of fairly common human genetic diseases in which enzymes required for the
breakdown of fructose, lactose, or sucrose are defective. However, there are very few cases of people
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?
48. Glycolysis
Page: 544 Difficulty: 2
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).
49. Glycolysis
Pages: 544-546 Difficulty: 1
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?
50. Glycolysis
Page: 546 Difficulty: 2
Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans, and
explain the circumstances that favor each.
51. Glycolysis
Page: 546 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+?
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
168
52. Glycolysis
Page: 547 Difficulty: 2
All of the intermediated in the glycolytic pathway are phosphorylated. Give two plausible reasons
why this might be advantageous to the cell.
53. Glycolysis
Pages: 545, 548–551 Difficulty: 3
Describe the glycolytic pathway from glucose to glyceraldehyde 3-phosphate. Show structures of
intermediates, enzyme names, and indicate where any cofactors participate.
54. Glycolysis
Pages: 545, 552–555 Difficulty: 3
Describe the glycolytic pathway from glyceraldehyde 3-phosphate to pyruvate, showing structures of
intermediates and names of enzymes. Indicate where any cofactors participate.
55. Glycolysis
Pages: 549–550 Difficulty: 2
What are the two reactions in glycolysis in which aldose to ketose isomerization is catalyzed by an
enzyme? For both reactions the G'° is positive. Briefly explain how the reactions are able to
proceed without the input of additional energy.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
169
56. Glycolysis
Page: 551 Difficulty: 3
What would be the products of the reaction, if aldolase used glucose-6-phosphate instead of fructose-
1,6-bisphosphate? Based on your answer, can you suggest a possible rationale for why nature chose to
include two extra steps prior to the aldolase step?
57. Glycolysis
Page: 545 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.
hexokinase
___ triose phosphate isomerase
___ phosphohexose isomerase
___ enolase
___ glyceraldehyde 3-phosphate dehydrogenase
___ pyruvate kinase
___ phosphofructokinase-1
Which of the enzymes represents a major regulation point in glycolysis?
Which catalyzes a reaction in which ATP is produced?
Which catalyzes a reaction in which NADH is produced?
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
170
58. Glycolysis
Page: 548 Difficulty: 2
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?
59. Glycolysis
Page: 552 Difficulty: 3
At which point in glycolysis do C-3 and C-4 of glucose become chemically equivalent?
60. Glycolysis
Pages: 551–552 Difficulty: 2
Explain why Pi (inorganic phosphate) is absolutely required for glycolysis to proceed.
61. Glycolysis
Page: 550 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. (R = 8.315 J/mol·K; T = 298 K)
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
171
62. Glycolysis
Page: 552 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.
63. Glycolysis
Page: 552 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.
64. Glycolysis
Pages: 551–552 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.
65. Glycolysis
Page: 550 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:
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
172
66. Glycolysis
Pages: 552–554 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.
67. Feeder pathways for glycolysis
Pages: 545, 560 Difficulty: 3
Yeast can metabolize D-mannose to ethanol and CO2. In addition to the glycolytic enzymes, the only
other enzyme needed is phosphomannose isomerase, which converts mannose 6-phosphate to fructose
6-phosphate. If mannose is converted to ethanol and CO2 by the most direct pathway, which of the
compounds and cofactors in this list are involved?
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
68. Feeder pathways for glycolysis
Page: 561 Difficulty: 3
Explain why the phosphorolysis of glycogen is more efficient than the hydrolysis of glycogen in
mobilizing glucose for the glycolytic pathway.
69. Feeder pathways for glycolysis
Pages: 560–561 Difficulty: 3
Describe the process of glycogen breakdown in muscle. Include a description of the structure of
glycogen, the nature of the breakdown reaction and the breakdown product, and the required
enzyme(s).
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
173
70. Feeder pathways for glycolysis
Page: 561 Difficulty: 2
Explain the biochemical basis of the human metabolic disorder called lactose intolerance.
71. Fates of pyruvate under anaerobic conditions: fermentation
Page: 565 Difficulty: 1
The yeast used in brewing the alcoholic beverage beer can break down glucose either aerobically or
anaerobically using alcoholic fermentation. Explain why beer is brewed under anaerobic conditions.
72. Fates of pyruvate under anaerobic conditions: fermentation
Page: 564 Difficulty: 2
Explain with words, diagrams, or structures why lactate accumulates in the blood during bursts of
very vigorous exercise (such as a 100-meter dash).
73. Fates of pyruvate under anaerobic conditions: fermentation
Page: 564 Difficulty: 2
Describe the fate of pyruvate, formed by glycolysis in animal skeletal muscle, under two conditions:
(a) at rest, and (b) during an all-out sprint. Show enough detail in your answer to explain why
pyruvate metabolism is different in these two cases.
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
174
74. Fates of pyruvate under anaerobic conditions: fermentation
Page: 564 Difficulty: 2
During strenuous activity, muscle tissue demands large quantities of ATP, compared with resting
muscle. In white skeletal muscle (in contrast with red muscle), ATP is produced almost exclusively
by fermentation of glucose to lactate. If a person had white muscle tissue devoid of the enzyme
lactate dehydrogenase, how would this affect his or her metabolism at rest and during strenuous
exercise?
to perform anaerobically.
75. Gluconeogenesis
Pages: 568–569 Difficulty: 1
What is gluconeogenesis, and what useful purposes does it serve in people?
76. Gluconeogenesis
Pages: 570–571 Difficulty: 2
If you incubate 14C-CO2 with liver extracts capable of performing gluconeogenesis, where does the
radioactive label end up?
77. Gluconeogenesis
Pages: 570–571 Difficulty: 3
In gluconeogenesis, how do animals convert pyruvate to phosphoenolpyruvate? Show structures,
enzymes, and cofactors.
78. The pentose phosphate pathway of glucose oxidation
Page: 575 Difficulty: 2
Rat liver is able to metabolize glucose by both the glycolytic and the pentose phosphate pathways.
Indicate in the blanks if the following are properties of glycolytic (G), pentose phosphate (P), both (G
+ P), or neither (0):
Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway
175
_____ NAD+ is involved.
_____ CO2 is liberated.
_____ Phosphate esters are intermediates.
_____ Glyceraldehyde 3-phosphate is an intermediate.
_____ Fructose 6-phosphate is an intermediate.
79. The pentose phosphate pathway of glucose oxidation
Page: 575 Difficulty: 2
The bacterium E. coli can grow in a medium in which the only carbon source is glucose. How does
this organism obtain ribose 5-phosphate for the synthesis of ATP? (Do not describe ATP synthesis,
just the origin of ribose 5-phosphate.) Show structures and indicate where cofactors participate.
80. The pentose phosphate pathway of glucose oxidation
Page: 575 Difficulty: 1
What are the biological functions of the pentose phosphate pathway?
81. The pentose phosphate pathway of glucose oxidation
Pages: 575–577 Difficulty: 3
An extract of adipose (fat) tissue can metabolize glucose to CO2. When glucose labeled with 14C in
either C-1 or C-6 was added to the extract, 14CO2 was released with the time courses shown below.
What is the major path of glucose oxidation in this extract? Explain how you reached this conclusion.
