1. Triose phosphate isomerase catalyzes this reaction:
dihydroxyacetone phosphate → glyceraldehyde-3-phosphate          ΔG°′ = 7.5 kJ/mol
a. What is K_eq for this reaction?
b. What must the ratio of [glyceraldehyde-3-phosphate]/[dihydroxyacetone-phosphate]
    be in a cell for ΔG to equal 0?
c. What is ΔG°′ for the reverse reaction?

2. ΔG°′ for the reaction catalyzed by hexokinase is − 16.7 kJ/mole.
a. Write the equilibrium expression for hexokinase.
b. What is K_eq for the reaction?
c. What must the [products]/[reactants] ratio be in a cell for ΔG to equal 0?
     What must the ratio be for ΔG to be negative?

3. During glycolysis this reaction has ΔG°′ = 6.3 kJ/mole:
glyceraldehyde-3-phosphate + phosphate → 1,3- bis-phosphoglycerate
The following reaction has ΔG°′ = − 12.5 kJ/mole:
1,3-bis-phosphoglycerate + ADP → ATP + 3-phosphoglycerate,
What is ΔG°′ for the following coupled reaction?
glyceraldehyde-3-phosphate + phosphate + ADP → 3-phosphoglycerate + ATP

4. Think of the reaction catalyzed by phosphoglycerate kinase as a coupled reaction that includes ATP synthesis (ΔG°′ = 30.5 kJ/mol). Based upon the information in question 3, what is ΔG°′ for the reaction 1,3-bis-phosphoglycerate → 3-phosphoglycerate + phosphate?

5. The G protein pathway involves converting GTP to GDP and ATP to cAMP.
a. What enzyme is required, and what is its energy cost, to convert GDP back to GTP?
b. What enzymes are required, and what is the total energy cost for converting cAMP
    to ADP?
Give energy cost in terms of the number of ATP's required, and assume ATP is present.

6. Oxidation of NADH can be coupled to reduction of oxaloacetate (→ malate)
(E°′= − 0.166 V), pyruvate (→ lactate) (E°′= − 0.185 V), or acetaldehyde → ethanol
(E°′= − 0.197 V). The reduction potential for   (NAD⁺ →) NADH = − 0.320 V.
a. Write the whole reaction for each of the coupled reactions.
b. Determine ΔE°′ for each whole reaction.
c. Given that ΔG°′ = − nF ΔE°′, and F = 96480 J/V-mol, which reaction is most favorable?

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