1. 1. Energyflow. What is the direction of each of the following reactions when the
reactants are initially present in equimolar amounts? Use the data given in the
2. A proper inference. What information do the ∆G° data given in Table 13.6
provide about the relative rates of hydrolysis of pyrophosphateand acetyl
2. 3. A potent donor. Consider the following reaction:
(a) Calculate ∆G° and K eq at 25°C for this reaction, by using the data given in
(b) What is the equilibrium ratio of pyruvate to phosphoenolpyruvate if the ratio of
ATP to ADP is 10?
4. Isomeric equilibrium. Calculate ∆G° for the isomerization of glucose 6-
phosphateto glucose 1-phosphate. What is the equilibrium ratio of glucose 6-
phosphateto glucose 1-phosphate at 25°C?
5. Activated acetate. The formation of acetyl CoA from acetate is an ATP-driven
(a) Calculate ∆G° for this reaction by using data given in this chapter.
(b) The PPi formed in the preceding reaction is rapidly hydrolyzed in vivo because
of the ubiquity of inorganic pyrophosphatase. The ∆G° for the hydrolysis of PPi is
-4.6 kcal mol-1. Calculate the ∆G° for the overall reaction.
What effect does the hydrolysis of PPi have on the formation of acetyl CoA?
6. Acid strength. The pK of an acid is a measure of its proton-group-transfer
(a) Derive a relation between ∆G° and pK.
(b) What is the ∆G° for the ionization of acetic acid, which has a pK of 4.8?
7. Raison d'être. The muscles of some invertebrates are rich in argininephosphate
(phosphoarginine). Proposea function for this amino acid derivative.
3. 8. Recurring motif. What is the structural feature common to ATP, FAD, NAD+,
9. Ergogenichelp or hindrance? Creatine is a popular, but untested, dietary
(a) What is the biochemical rationale for the use of creatine?
(b) What type of exercise would most benefit from creatine supplementation?
10. Standardconditions versus real life. The enzyme aldolase catalyzes the
following reaction in the glycolytic pathway:
G° for the reaction is +5.7 kcal mol- G in the cell is -0.3
kcal mol-1. Calculate the ratio of reactants to products under equilibrium and
intracellular conditions. Using your results, explain how the reaction can be
endergonic under standard conditions and exergonic under intracellular conditions.
11. Not all alike. The concentrations of ATP, ADP, and Pi differ with cell type.
Consequently, the release of free energy with the hydrolysis of ATP will vary with
G for the hydrolysis of ATP
in muscle, liver, and brain cells. In which cell type is the free energy of ATP
4. 12. Runningdownhill. Glycolysis is a series of 10 linked reactions that convert one
molecule of glucose into two molecules of pyruvate with the concomitant synthesis
of two mole G° for this set of reactions is -8.5
kcal mol-1 (-35.6 kJ mol- G is -18.3 kcal mol-1 (-76.6 kJ mol-
1). Explain why the free-energy release is so much greater under intracellular
conditions than under standard conditions.
Chapter Integration Problem
13. Activated sulfate. Fibrinogen contains tyrosine-O-sulfate. Proposean activated
form of sulfate that could react in vivo with the aromatic hydroxyl group of a
tyrosine residue in a protein to form tyrosine-O-sulfate.
14. Opposites attract G for the hydrolysis
of ATP varies as a function of the Mg2+ concentration (pMg = log 1/[Mg2+]).
G of hydrolysis for ATP?
(b) How can you explain this effect?
1. Reactions in parts a and c, to the left; reactions in parts b and d, to the right.
2. None whatsoever.
5. 3. G° = +7.5 kcal mol-1 (+31.4 kJ mol-1) and K eq = 3.2 × 10-6. (b) 3.28 ×
4. G° = -1.7 kcal mol-1 (-7.1 kJ mol-1). The equilibrium ratio is 17.8.
5. G° = +7.5 kcal mol-1
(+31.4 kJ mol- G° = -10.9 kcal mol-1 (-45.6 kJ mol-1).
G° = -3.4 kcal mol-1 (-14.2 kJ mol-1).
G° = -8.0 kcal mol-1 (-33.4 kJ mol-1).
6. (a) The pK is defined as pK = -log10 K G° is the standard free energy
change at pH 7. G° = -RT ln K = -2.303 log10 K = -2.303 (pK - 7) kcal
mol-1 since [H+] = 10-7 M.
G° = -2.303 (4.8 - 7) = -5.1 kcal mol-1 (-21.3 kJ mol-1).
7. Arginine phosphatein invertebrate muscle, like creatine phosphatein vertebrate
muscle, serves as a reservoir of highpotential phosphorylgroups. Arginine
phosphatemaintains a high level of ATP in muscular exertion.
8. An ADP unit.
9. (a) The rationale behind creatine supplementation is that it would be converted
into creatine phosphate and thus serves as a rapid means of replenishing ATP after
(b) If it is beneficial, it would affect activities that depend on short bursts of
activity; any sustained activity would require ATP generation by fuel metabolism,
which, as Figure 14.7 shows, requires more time.
10. G° = -RT ln [product]/[reactants]. Substituting
+5.7 kcal mol- G° and solving for [products]/[reactants] yields 7 × 10-5.
In other words, the forward reaction does not take place to a significant extent.
G is 0.3 kcal mol-1. If one uses the equation
G G° + RT ln [product]/[reactants] and solves for [products]/[reactants],
the ratio is 3.7 × 10-5. Thus, a reaction that is endergonic under standard
6. conditions can be converted into an exergonic reaction by maintaining the
[products]/[reactants]ratio below the equilibrium value. This conversion is usually
attained by using the products in another coupled reaction as soonas they are
11. Liver: -10.8 kcal mol-1 (-45.2 kJ mol-1); muscle: -11.5 kcal mol-1 (-47.8 kJ
mol-1); brain: -11.6 kcal mol-1(-48.4 kJ mol-1).
12. G G° + RT ln [products/reactants]. Altering the ratio of
G to vary. In glycolysis, the concentrations of
G greater than that of
13. The activated form of sulfate in most organisms is 3 -phosphoadenosine5 -
14. G of hydrolysis rises. Note that
pMg is a logarithmic plot, and so each number on the x-axis represents a 10-fold
change in [Mg2+].
(b) Mg2+ would bind to the phosphates of ATP and help to mitigate charge
repulsion. As the [Mg2+] falls, charge stabilization of ATP would be less, leading
G on hydrolysis.