Deck 13: Principles of Bioenergetics

Question 1

For the following reaction, $\Delta$ G'° = +29.7 kJ/mol.
L-Malate + NAD⁺ $\rightarrow$ 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 $\Delta$ 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.

Answer 1

may occur in cells at some concentrations of substrate and product.

Question 2

For the reaction A $\rightarrow$ B, $\Delta$ 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 $\Delta$ G'° is -60 kJ/mol.

Answer 2

B formation is kinetically slow;equilibrium has not been reached by 24 hours.

Question 3

The $\Delta$ G'° values for the two reactions shown below are given.

What is the $\Delta$ G'° for the hydrolysis of acetyl-CoA?
Acetyl-CoA + H₂O $\rightarrow$ acetate + CoASH + H⁺

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

Answer 3

-30.3 kJ/mol

Question 4

Which of the following is true about oxidation-reduction reactions?

A)They usually proceed through homolytic cleavage.
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.

Question 5

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 $\rightarrow$ fructose 6-phosphate

A)( $\Delta$ G'° is incalculably large and negative.)
B)( $\Delta$ G'° is -1.72 kJ/mol.)
C)( $\Delta$ G'° is zero.)
D)( $\Delta$ G'° is +1.72 kJ/mol.)
E)( $\Delta$ G'° is incalculably large and positive.)

Question 6

During glycolysis,glucose 1-phosphate is converted to fructose 6-phosphate in two successive reactions:
Glucose 1-phosphate $\rightarrow$ glucose 6-phosphate $\Delta$ G'° = -7.1 kJ/mol
Glucose 6-phosphate $\rightarrow$ fructose 6-phosphate $\Delta$ G'° = +1.7 kJ/mol
$\Delta$ 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.

Question 7

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

Question 8

Which of the following compounds has the largest negative value for the standard free-energy change ( $\Delta$ G'°)upon hydrolysis?

A)Acetic anhydride
B)Glucose 6-phosphate
C)Glutamine
D)Glycerol 3-phosphate
E)Lactose

Question 9

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 $\alpha$ -keto acid goes through a carbocation intermediate.
E)A Claisen ester condensation reaction goes through a carbanion intermediate.

Question 10

Which of the following is not nucleophilic?

A)A proton
B)A carbanion
C)An imidazole
D)A hydroxide
E)A carboxylic acid

Question 11

For the reaction A $\rightarrow$ B,the K_eq' 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)( $\Delta$ G'° for the reaction will be large and positive.)

Question 12

The standard free-energy changes for the reactions below are given.
Phosphocreatine $\rightarrow$ creatine + P_i $\Delta$ G'° = -43.0 kJ/mol
ATP $\rightarrow$ ADP + P_i $\Delta$ G'° = -30.5 kJ/mol
What is the overall $\Delta$ G'° for the following reaction?
Phosphocreatine + ADP $\rightarrow$ creatine + ATP

A)-73.5 kJ/mol
B)-12.5 kJ/mol
C)+12.5 kJ/mol
D)+73.5 kJ/mol
E)( $\Delta$ G'° cannot be calculated without K_eq'.)

Question 13

The reaction A + B $\rightarrow$ C has a $\Delta$ 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.

Question 14

If the $\Delta$ G'° of the reaction A $\rightarrow$ 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.

Question 15

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.

Question 16

In glycolysis,fructose 1,6-bisphosphate is converted to two products with a standard free-energy change ( $\Delta$ G'°)of 23.8 kJ/mol.Under what conditions encountered in a normal cell will the free-energy change ( $\Delta$ 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 $\Delta$ 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.

Question 17

The reaction ATP $\rightarrow$ ADP + P_i is an example of a reaction.

A)homolytic cleavage
B)internal rearrangement
C)free radical
D)group transfer
E)oxidation/reduction

Question 18

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)( $\Delta$ G'° is -11 kJ/mol.)
B)( $\Delta$ G'° is -5 kJ/mol.)
C)( $\Delta$ G'° is 0 kJ/mol.)
D)( $\Delta$ G'° is +11 kJ/mol.)
E)( $\Delta$ G'° cannot be determined from the information given.)

Question 19

For the reaction A $\rightarrow$ B,the K_eq' 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)( $\Delta$ G'° for the reaction will be large and positive.)

Question 20

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 $\rightarrow$ 2-phosphoglycerate

A)( $\Delta$ G'° is -4.44 kJ/mol.)
B)( $\Delta$ G'° is zero.)
C)( $\Delta$ G'°is +12.7 kJ/mol.)
D)( $\Delta$ G'°is incalculably large and positive.)
E)( $\Delta$ G'° cannot be calculated from the information given.)

Question 21

Bioenergetics and thermodynamics
What is the difference between $\Delta$ G and $\Delta$ G'° of a chemical reaction? Describe,quantitatively,the relationship between them.

Question 22

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)

Question 23

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.

Question 24

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 K_eq' and $\Delta$ G'° for this reaction (in the direction of glucose 6-phosphate formation).(R = 8.315 J/mol·K;T = 298 K)

Question 25

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.

Question 26

The hydrolysis of phosphoenolpyruvate proceeds with a $\Delta$ 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.

Question 27

Explain in quantitative terms the circumstances under which the following reaction can proceed.
Citrate $\rightarrow$ isocitrate $\Delta$ G'° = +13.3 kJ/mol

Question 28

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.

Question 29

The hydrolysis of ATP has a large negative $\Delta$ 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.

Question 30

The immediate precursors of DNA and RNA synthesis in the cell all contain:

A)3' triphosphates.
B)5' triphosphates.
C)adenine.
D)deoxyribose.
E)ribose.

Question 31

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.

Question 32

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⁺ $\rightarrow$ oxaloacetate + NADH + H⁺.
B)malate + NADH + H⁺ $\rightarrow$ oxaloacetate + NAD⁺.
C)NAD⁺ + NADH + H⁺ $\rightarrow$ malate + oxaloacetate.
D)NAD⁺ + oxaloacetate $\rightarrow$ NADH + H⁺ + malate.
E)oxaloacetate + NADH + H⁺ $\rightarrow$ malate + NAD⁺.

Question 33

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.

Question 34

The expression $\Delta$ G = $\Delta$ G'° + RT ln K_eq' for the actual free-energy change for the reaction A + B $\rightarrow$ C + D is incorrect.Why is it wrong,and what is the correct expression for the real free-energy change of this reaction?

Question 35

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.

Question 36

Consider the reaction: A + B $\rightarrow$ C + D.If the equilibrium constant for this reaction is a large number (say,10,000),what do we know about the standard free-energy change ( $\Delta$ G'°)for the reaction? Describe the relationship between K_eq' and $\Delta$ G'°.

Question 37

The standard free energy change ( $\Delta$ G'°)for ATP hydrolysis is -30.5 kJ/mol.ATP,ADP,and P_i are mixed together at initial concentrations of 1 M of each,then left alone until the reaction ADP + P_i $\rightarrow$ ATP has come to equilibrium.For each species (i.e. ,ATP,ADP,and P_i),indicate whether the concentration will be equal to 1 M,less than 1 M,or greater than 1 M.

Question 38

The standard reduction potentials (E'°)for the following half reactions are given.
Fumarate + 2H⁺ + 2e^- $\rightarrow$ succinate E'° = +0.031 V
FAD + 2H⁺ + 2e^- $\rightarrow$ 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 concentrations.
D)Succinate would become oxidized;FAD would become reduced.
E)Succinate would become oxidized;FADH₂ would be unchanged because it is a cofactor.

Question 39

In glycolysis,the enzyme pyruvate kinase catalyzes this reaction:
Phosphoenolpyruvate + ADP $\rightarrow$ 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 $\rightarrow$ ADP + P_i $\Delta$ G'° = -30.5 kJ/mol
Reaction 2)phosphoenolpyruvate $\rightarrow$ pyruvate + P_i $\Delta$ G'° = -61.9 kJ/mol

Question 40

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 $\Delta$ G'° is positive,K_eq' > 1.
(c) $\Delta$ G and $\Delta$ G'° mean the same thing.
(d)When $\Delta$ G'° = 1.0 kJ/mol,K_eq' = 1.

Question 41

The free energy of hydrolysis of phosphoenolpyruvate is -61.9 kJ/mol.Rationalize this large,negative value for $\Delta$ G'° in chemical terms.

Question 42

Why is the actual free energy ( $\Delta$ G)of hydrolysis of ATP in the cell different from the standard free energy ( $\Delta$ G'°)?

Question 43

If $\Delta$ E'° for an oxidation-reduction reaction is positive,will $\Delta$ G'° be positive or negative? What is the equation that relates $\Delta$ G'° and $\Delta$ E'°?

Question 44

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

Question 45

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 transduction that occur in living organisms and provide one example for each.

Question 46

During transfer of two electrons through the mitochondrial respiratory chain,the overall reaction is:
NADH + 1/2 O₂ + H⁺ $\rightarrow$ NAD⁺ + H₂O
For this reaction,the difference in reduction potentials for the two half-reactions ( $\Delta$ E'°)is +1.14 V.Show how you would calculate the standard free-energy change, $\Delta$ G'°,for the reaction.(The Faraday constant,,is 96.48 kJ/V·mol. )

Question 47

Alcohol dehydrogenase catalyzes the following reversible reaction:
Acetaldehyde + NADH + H⁺ $\rightarrow$ Ethanol + NAD⁺
Use the following information to answer the questions below:

The Faraday constant, ,is 96.48 kJ/V·mol.
(a)Calculate $\Delta$ G'° for the reaction as written.Show your work.
(b)Given your answer to (a),what is the $\Delta$ 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 $\Delta$ G'°.Explain how this could be possible.

Question 48

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.

Question 49

Classify each of the *ed atoms as an electrophile or a nucleophile:

Question 50

What is an oxidation? What is a reduction? Can an oxidation occur without a simultaneous reduction? Why or why not?

Question 51

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.

Question 52

Glycerol 3-phosphate dehydrogenase catalyzes the following reversible reaction:
Glycerol 3-phosphate + NAD⁺ $\rightarrow$ NADH + H⁺ + dihydroxyacetone phosphate
Given the standard reduction potentials below,calculate $\Delta$ G'° for the glycerol 3-phosphate dehydrogenase reaction,proceeding from left to right as shown.Show your work.(The Faraday constant,F,is 96.48 kJ/V·mol. )

Question 53

Lactate dehydrogenase catalyzes the reversible reaction:
Pyruvate + NADH + H⁺ $\rightarrow$ 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 $\Delta$ G'° for this reaction.Show your work.