Chapter 13 Principles of Bioenergetics
Multiple Choice Questions
1. Bioenergetics and thermodynamics
If the G’° of the reaction A → B is –40 kJ/mol, under standard conditions the reaction:
A) is at equilibrium.
B) will never reach equilibrium.
C) will not occur spontaneously.
D) will proceed at a rapid rate.
E) will proceed spontaneously from A to B.
2. Bioenergetics and thermodynamics
For the reaction A → B, G’° = –60 kJ/mol. The reaction is started with 10 mmol of A; no B is
initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A. Which
is the most likely explanation?
A) A and B have reached equilibrium concentrations.
B) An enzyme has shifted the equilibrium toward A.
C) B formation is kinetically slow; equilibrium has not been reached by 24 hours.
D) Formation of B is thermodynamically unfavorable.
E) The result described is impossible, given the fact that G’° is –60 kJ/mol.
3. Bioenergetics and thermodynamics
When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25 °C with
phosphoglycerate mutase until equilibrium is reached, the final mixture contains six times as much 2–
phosphoglycerate as 3-phosphoglycerate. Which one of the following statements is most nearly
correct, when applied to the reaction as written? (R = 8.315 J/mol·K; T = 298 K)
3-Phosphoglycerate → 2-phosphoglycerate
A) G’° is –4.44 kJ/mol.
B) G’° is zero.
C) G’°is +12.7 kJ/mol.
D) G’°is incalculably large and positive.
E) G’° cannot be calculated from the information given.
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4. Bioenergetics and thermodynamics
When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme
phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until
equilibrium is reached, the final mixture contains twice as much glucose 6-phosphate as fructose 6-
phosphate. Which one of the following statements is best applied to this reaction outlined below?
(R = 8.315 J/mol·K; T = 298 K)
Glucose 6-phosphate → fructose 6-phosphate
A) G’° is incalculably large and negative.
B) G’° is –1.72 kJ/mol.
C) G’° is zero.
D) G’° is +1.72 kJ/mol.
E) G’° is incalculably large and positive.
5. Bioenergetics and thermodynamics
Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6-phosphatase is 99% complete at
equilibrium (i.e., only 1% of the substrate remains). Which of the following statements is most nearly
correct? (R = 8.315 J/mol·K; T = 298 K)
A) G’° is –11 kJ/mol.
B) G’° is –5 kJ/mol.
C) G’° is 0 kJ/mol.
D) G’° is +11 kJ/mol.
E) G’° cannot be determined from the information given.
6. Bioenergetics and thermodynamics
The reaction A + B → C has a G’° of –20 kJ/mol at 25° C. Starting under standard conditions, one
can predict that:
A) at equilibrium, the concentration of B will exceed the concentration of A.
B) at equilibrium, the concentration of C will be less than the concentration of A.
C) at equilibrium, the concentration of C will be much greater than the concentration of A or B.
D) C will rapidly break down to A + B.
E) when A and B are mixed, the reaction will proceed rapidly toward formation of C.
7. Bioenergetics and thermodynamics
Which of the following compounds has the largest negative value for the standard free-energy change
(G’°) upon hydrolysis?
A) Acetic anhydride
B) Glucose 6-phosphate
C) Glutamine
D) Glycerol 3-phosphate
E) Lactose
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8. Bioenergetics and thermodynamics
For the following reaction, G’° = +29.7 kJ/mol.
L-Malate + NAD+ → oxaloacetate + NADH + H+
The reaction as written:
A) can never occur in a cell.
B) can occur in a cell only if it is coupled to another reaction for which G’° is positive.
C) can occur only in a cell in which NADH is converted to NAD+ by electron transport.
D) cannot occur because of its large activation energy.
E) may occur in cells at some concentrations of substrate and product.
9. Bioenergetics and thermodynamics
For the reaction A → B, the Keq‘ is 104. If a reaction mixture originally contains 1 mmol of A and no
B, which one of the following must be true?
A) At equilibrium, there will be far more B than A.
B) The rate of the reaction is very slow.
C) The reaction requires coupling to an exergonic reaction in order to proceed.
D) The reaction will proceed toward B at a very high rate.
E) G’° for the reaction will be large and positive.
10. Bioenergetics and thermodynamics
For the reaction A → B, the Keq‘ is 10-6. If a reaction mixture originally contains 1 mmol of A and 1
mmol of B, which one of the following must be true?
A) At equilibrium, there will be still be equal levels of A and B.
B) The rate of the reaction is very slow.
C) At equilibrium, the amount of A will greatly exceed the amount of B.
D) The reaction will proceed toward B at a very high rate.
E) G’° for the reaction will be large and positive.
11. Bioenergetics and thermodynamics
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 spontaneously to the right?
A) Under standard conditions, enough energy is released to drive the reaction to the right.
B) The reaction will not go to the right spontaneously under any conditions because the G’° is
positive.
C) The reaction will proceed spontaneously to the right if there is a high concentration of products
relative to the concentration of fructose 1,6-bisphosphate.
D) The reaction will proceed spontaneously to the right if there is a high concentration of fructose
1,6-bisphosphate relative to the concentration of products.
E) None of the above conditions is sufficient.
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12. Bioenergetics and thermodynamics
During glycolysis, glucose 1-phosphate is converted to fructose 6-phosphate in two successive reactions:
Glucose 1-phosphate → glucose 6-phosphate G’° = –7.1 kJ/mol
Glucose 6-phosphate → fructose 6-phosphate G’° = +1.7 kJ/mol
G’° for the overall reaction is:
A) –8.8 kJ/mol.
B) –7.1 kJ/mol.
C) –5.4 kJ/mol.
D) +5.4 kJ/mol.
E) +8.8 kJ/mol.
13. Bioenergetics and thermodynamics
The standard free-energy changes for the reactions below are given.
Phosphocreatine → creatine + Pi G’° = –43.0 kJ/mol
ATP → ADP + Pi G’° = –30.5 kJ/mol
What is the overall G’° for the following reaction?
Phosphocreatine + ADP → creatine + ATP
A) –73.5 kJ/mol
B) –12.5 kJ/mol
C) +12.5 kJ/mol
D) +73.5 kJ/mol
E) G’° cannot be calculated without Keq‘.
14. Bioenergetics and thermodynamics
The G’° values for the two reactions shown below are given.
Oxaloacetate + acetyl-CoA + H2O ⎯⎯→ citrate + CoASH G’° = –32.2 kJ/mol
citrate
synthase
Oxaloacetate + acetate ⎯⎯→ citrate G’° = –1.9 kJ/mol
citrate lyase
What is the G’° for the hydrolysis of acetyl-CoA?
Acetyl-CoA + H2O ⎯⎯→ acetate + CoASH + H+
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A) -34.1 kJ/mol
B) -32.2 kJ/mol
C) -30.3 kJ/mol
D) +61.9 kJ/mol
E) +34.1 kJ/mol
15. Chemical Logic and Common Biochemical Reactions
Which of the following is not nucleophilic?
A) A proton
B) A carbanion
C) An imidazole
D) A hydroxide
E) A carboxylic acid
16. Chemical Logic and Common Biochemical Reactions
Which of the following is not electrophilic?
A) A proton
B) A sulfhydryl
C) A protonated imine
D) A carbonyl group
E) A phosphoryl group
17. Chemical Logic and Common Biochemical Reactions
Which of the following is not true?
A) The carbon adjacent to a carbonyl can be resonance stabilized to form a carbanion.
B) A carbonyl carbon can be made more electrophilic by a nearby metal ion.
C) The carbon adjacent to an imine can be resonance stabilized to form a carbanion
D) Decarboxylation of an -keto acid goes through a carbocation intermediate.
E) A Claisen ester condensation reaction goes through a carbanion intermediate.
18. Chemical Logic and Common Biochemical Reactions
The reaction ATP → ADP + Pi is an example of a reaction.
A) homolytic cleavage
B) internal rearrangement
C) free radical
D) group transfer
E) oxidation/reduction
19. Chemical Logic and Common Biochemical Reactions
Which of the following is true about oxidation-reduction reactions?
A) They usually proceed through homolytic cleavage.
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B) During oxidation a compound gains electrons.
C) Dehydrogenases typically remove two electrons and two hydrides.
D) There are four commonly accessed oxidation states of carbon.
E) Every oxidation must be accompanied by a reduction.
20. Phosphoryl group transfers and ATP
All of the following contribute to the large, negative, free–energy change upon hydrolysis of “high–
energy” compounds except:
A) electrostatic repulsion in the reactant.
B) low activation energy of forward reaction.
C) stabilization of products by extra resonance forms.
D) stabilization of products by ionization.
E) stabilization of products by solvation.
21. Phosphoryl group transfers and ATP
The hydrolysis of ATP has a large negative G’°; nevertheless it is stable in solution due to:
A) entropy stabilization.
B) ionization of the phosphates.
C) resonance stabilization.
D) the hydrolysis reaction being endergonic.
E) the hydrolysis reaction having a large activation energy.
22. Phosphoryl group transfers and ATP
The hydrolysis of phosphoenolpyruvate proceeds with a G’° of about –62 kJ/mol. The greatest
contributing factors to this reaction are the destabilization of the reactants by electostatic repulsion
and stabilization of the product pyruvate by:
A) electrostatic attraction.
B) ionization.
C) polarization.
D) resonance.
E) tautomerization.
23. Phosphoryl group transfers and ATP
Which one of the following compounds does not have a large negative free energy of hydrolysis?
A) 1,3-bis phosphoglycerate
B) 3-phosphoglycerate
C) ADP
D) Phosphoenolpyruvate
E) Thioesters (e.g. acetyl-CoA)
24. Phosphoryl group transfers and ATP
The immediate precursors of DNA and RNA synthesis in the cell all contain:
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A) 3′ triphosphates.
B) 5′ triphosphates.
C) adenine.
D) deoxyribose.
E) ribose.
25. Phosphoryl group transfers and ATP
Muscle contraction involves the conversion of:
A) chemical energy to kinetic energy.
B) chemical energy to potential energy.
C) kinetic energy to chemical energy.
D) potential energy to chemical energy.
E) potential energy to kinetic energy.
26. Biological oxidation-reduction reactions
Biological oxidation-reduction reactions always involve:
A) direct participation of oxygen.
B) formation of water.
C) mitochondria.
D) transfer of electron(s).
E) transfer of hydrogens.
27. Biological oxidation-reduction reactions
Biological oxidation-reduction reactions never involve:
A) transfer of e– from one molecule to another.
B) formation of free e–.
C) transfer of H+ (or H3O+) from one molecule to another.
D) formation of free H+ (or H3O+).
E) none of the above.
28. Biological oxidation-reduction reactions
The standard reduction potentials (E’°) for the following half reactions are given.
Fumarate + 2H+ + 2e– → succinate E’° = +0.031 V
FAD + 2H+ + 2e– → FADH2 E’° = –0.219 V
If you mixed succinate, fumarate, FAD, and FADH2 together, all at l M concentrations and in the
presence of succinate dehydrogenase, which of the following would happen initially?
A) Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced.
B) Fumarate would become reduced; FADH2 would become oxidized.
C) No reaction would occur because all reactants and products are already at their standard
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concentrations.
D) Succinate would become oxidized; FAD would become reduced.
E) Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor.
29. Biological oxidation-reduction reactions
E’° of the NAD+/NADH half reaction is –0.32 V. The E’° of the oxaloacetate/malate half reaction is
–0.175 V. When the concentrations of NAD+, NADH, oxaloacetate, and malate are all 10–5 M, the
“spontaneous” reaction is:
A) malate + NAD+ → oxaloacetate + NADH + H+.
B) malate + NADH + H+ → oxaloacetate + NAD+.
C) NAD+ + NADH + H+ → malate + oxaloacetate.
D) NAD+ + oxaloacetate → NADH + H+ + malate.
E) oxaloacetate + NADH + H+ → malate + NAD+.
30. Biological oxidation-reduction reactions
The structure of NAD+ does not include:
A) a flavin nucleotide.
B) a pyrophosphate bond.
C) an adenine nucleotide.
D) nicotinamide.
E) two ribose residues.
31. Biological oxidation-reduction reactions
Which of the following is not true for the nicotinamide cofactors?
A) The oxidized form is positively charged.
B) The reduced form has a large extinction coefficient at 340 nm.
C) The oxidized form provides reducing equivalents to other molecules.
D) Oxidation-reduction reactions with nicotinamides usually involve hydride transfer.
E) Enzymes transfer hydrides stereospecifically to one or the other side of the nicotinamide ring.
Short Answer Questions
32. Bioenergetics and thermodynamics
Pages: 506–307 Difficulty: 2
Explain the relationships among the change in the degree of order, the change in entropy, and the
change in free energy that occur during a chemical reaction.
33. Bioenergetics and thermodynamics
Pages: 507–508 Difficulty: 2
Consider the reaction: A + B → C + D. If the equilibrium constant for this reaction is a large number
Chapter 13 Principles of Bioenergetics
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(say, 10,000), what do we know about the standard free-energy change (G’°) for the reaction?
Describe the relationship between Keq‘ and G’°.
34. Bioenergetics and thermodynamics
Page: 508 Difficulty: 2
The standard free energy change (G’°) for ATP hydrolysis is –30.5 kJ/mol. ATP, ADP, and Pi are
mixed together at initial concentrations of 1 M of each, then left alone until the reaction ADP + Pi →
ATP has come to equilibrium. For each species (i.e., ATP, ADP, and Pi), indicate whether the
concentration will be equal to 1 M, less than 1 M, or greater than 1 M.
35. Bioenergetics and thermodynamics
Page: 508 Difficulty: 3
If a 0.1 M solution of glucose 1-phosphate is incubated with a catalytic amount of phospho–
glucomutase, the glucose 1-phosphate is transformed to glucose 6-phosphate until equilibrium is
reached. At equilibrium, the concentration of glucose 1-phosphate is 4.5 x 10–3 M and that of glucose
6-phosphate is 8.6 10–2 M. Set up the expressions for the calculation of Keq‘ and G’° for this
reaction (in the direction of glucose 6-phosphate formation). (R = 8.315 J/mol·K; T = 298 K)
36. Bioenergetics and thermodynamics
Page: 508 Difficulty: 2
What is the difference between G and G’° of a chemical reaction? Describe, quantitatively, the
relationship between them.
37. Bioenergetics and thermodynamics
Page: 508 Difficulty: 2
The expression G = G’° + RT ln Keq‘ for the actual free-energy change for the reaction A + B → C
+ D is incorrect. Why is it wrong, and what is the correct expression for the real free-energy change
of this reaction?
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concentrations represent the equilibrium concentrations. In this situation, G = 0.
38. Bioenergetics and thermodynamics
Page: 509 Difficulty: 3
Explain in quantitative terms the circumstances under which the following reaction can proceed.
Citrate → isocitrate G’° = +13.3 kJ/mol
39. Bioenergetics and thermodynamics
Pages: 506–509 Difficulty: 2
Explain why each of the following statements is false.
(a) In a reaction under standard conditions, only the reactants are fixed at 1 M.
(b) When G’° is positive, Keq‘ > 1.
(c) G and G’° mean the same thing.
(d) When G’° = 1.0 kJ/mol, Keq‘ = 1.
40. Bioenergetics and thermodynamics
Pages: 408–511 Difficulty: 3
In glycolysis, the enzyme pyruvate kinase catalyzes this reaction:
Phosphoenolpyruvate + ADP → pyruvate + ATP
Given the information below, show how you would calculate the equilibrium constant for this
reaction. (R = 8.315 J/mol·K; T = 298 K)
Reaction 1) ATP → ADP + Pi G’° = –30.5 kJ/mol
Reaction 2) phosphoenolpyruvate → pyruvate + Pi G’° = –61.9 kJ/mol
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41. Bioenergetics and thermodynamics
Page: 510 Difficulty: 2
Explain what is meant by the statement: “Standard free–energy changes are additive.” Give an
example of the usefulness of this additive property in understanding how cells carry out
thermodynamically unfavorable chemical reactions.
42. Bioenergetics and thermodynamics
Pages: 508–511 Difficulty: 2
Given G’° for each of the following reactions,
1. ATP → ADP + Pi G’° = –30.5 kJ/mol
2. glucose 6-phosphate → glucose + Pi G’° = –13.8 kJ/mol
show how you would calculate the standard free-energy change (G’°) for the reaction:
3. ATP + glucose → glucose 6-phosphate + ADP
43. Chemical Logic and Common Biochemical Reactions
Page: 512 Difficulty: 2
Classify each of the *ed atoms as an electrophile or a nucleophile:
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(a) (b) (c) (d) (e)
H O
N
CH3
CH3
CH3
O
N
*
*
*
*
*
44. Phosphoryl group transfers and ATP
Pages: 517–519 Difficulty: 2
Why is the actual free energy (G) of hydrolysis of ATP in the cell different from the standard free
energy (G’°)?
45. Phosphoryl group transfers and ATP
Page: 520 Difficulty: 2
The free energy of hydrolysis of phosphoenolpyruvate is –61.9 kJ/mol. Rationalize this large,
negative value for G’° in chemical terms.
46. Phosphoryl group transfers and ATP
Page: 522 Difficulty: 3
In general, when ATP hydrolysis is coupled to an energy-requiring reaction, the actual reaction often
consists of the transfer of a phosphate group from ATP to another substrate, rather than an actual
hydrolysis of the ATP. Explain.
47. Phosphoryl group transfers and ATP
Pages: 524–526 Difficulty: 2
The first law of thermodynamics states that the amount of energy in the universe is constant, but that
the various forms of energy can be interconverted. Describe four different types of such energy
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transduction that occur in living organisms and provide one example for each.
48. Biological oxidation-reduction reactions
Page: 528 Difficulty: 1
What is an oxidation? What is a reduction? Can an oxidation occur without a simultaneous
reduction? Why or why not?
49. Biological oxidation-reduction reactions
Page: 531 Difficulty: 3
During transfer of two electrons through the mitochondrial respiratory chain, the overall reaction is:
NADH + 1/2 O2 + H+ → NAD+ + H2O
For this reaction, the difference in reduction potentials for the two half-reactions (E’°) is +1.14 V.
Show how you would calculate the standard free-energy change, G’°, for the reaction. (The Faraday
constant, , is 96.48 kJ/V·mol.)
50. Biological oxidation-reduction reactions
Page: 531 Difficulty: 2
If E’° for an oxidation-reduction reaction is positive, will G’° be positive or negative? What is the
equation that relates G’° and E’°?
51. Biological oxidation-reduction reactions
Pages: 531–532 Difficulty: 2
Glycerol 3-phosphate dehydrogenase catalyzes the following reversible reaction:
Glycerol 3-phosphate + NAD+ → NADH + H+ + dihydroxyacetone phosphate
Given the standard reduction potentials below, calculate G’° for the glycerol 3-phosphate
dehydrogenase reaction, proceeding from left to right as shown. Show your work. (The Faraday
constant, , is 96.48 kJ/V·mol.)
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Dihydroxyacetone phosphate + 2e– + 2H+ → glycerol 3-phosphate E’° = –0.29 V
NAD+ + H+ + 2e– → NADH E’° = –0.32 V
52. Biological oxidation-reduction reactions
Page: 531 Difficulty: 1
For each pair of ions or compounds below, indicate which is the more highly reduced species.
(a) Co2+/Co+
(b) Glucose/CO2
(c) Fe3+/Fe2+
(d) Acetate/CO2
(e) Ethanol/acetic acid
(f) Acetic acid/acetaldehyde
53. Biological oxidation-reduction reactions
Pages: 531–532 Difficulty: 3
Lactate dehydrogenase catalyzes the reversible reaction:
Pyruvate + NADH + H+ → Lactate + NAD+
Given the following facts (a) tell in which direction the reaction will tend to go if NAD+, NADH,
pyruvate, and lactate were mixed, all at 1 M concentrations, in the presence of lactate dehydrogenase
at pH 7; (b) calculate G’° for this reaction. Show your work.
NAD+ + H+ + 2e– → NADH E’° = –0.32 V
pyruvate + 2H+ + 2e– → lactate E’° = –0.19 V
The Faraday constant, , is 96.48 kJ/V·mol.
54. Biological oxidation-reduction reactions
Pages: 531–532 Difficulty: 3
Alcohol dehydrogenase catalyzes the following reversible reaction:
Acetaldehyde + NADH + H+ → Ethanol + NAD+
Use the following information to answer the questions below:
Acetaldehyde + 2H+ + 2e– → ethanol E’° = –0.20 V
NAD+ + H+ + 2e– → NADH E’° = –0.32 V
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The Faraday constant, , is 96.48 kJ/V·mol.
(a) Calculate G’° for the reaction as written. Show your work.
(b) Given your answer to (a), what is the G’° for the reaction occurring in the reverse direction?
(c) Which reaction (forward or reverse) will tend to occur spontaneously under standard conditions?
(d) In the cell, the reaction actually proceeds in the direction that has a positive G’°. Explain how
this could be possible.