1. a) Give the net equation of the citric acid cycle under normal aerobic conditions, starting with acetyl CoA.
b) Approximately how many ATP or GTP equivalents will be produced from energy molecules produced during one turn of the citric acid cycle? Assume that 1 NADH produces 2.5 ATPs and 1 FADH2 produces 1.5 ATPs at the end of the electron transport chain and the ATP synthase steps. Show your calculations.
c) What is the purpose of reactions 5 through 8?
d) How many ATP equivalents are produced from the total oxidation of 1 pyruvate?
2. What is the energy source that drives the condensation of oxaloacetate and acetyl-CoA to produce citrate?
3. List the five coenzymes that are required for the oxidative decarboxylation of pyruvate and α-ketoglutarate and give the essential nutrient (vitamin) that is required for each.
4. Give the reaction in the citric acid cycle by which the energy is conserved in the formation of a phosphoanhydride bond by substrate level phosphorylation. Give the name of the enzyme that catalyzes this reaction and give the structures of the reactants and products of this reaction.
5. Why is it necessary that there be a mechanism to replenish oxaloacetate?
6. How does the decarboxylation of α-ketoglutarate resemble that of pyruvate decarboxylation?
7. The ΔG°′ = -21 kJ/mol for the reaction catalyzed by isocitrate dehydrogenase, yet the ΔG°′ = +29.7 kJ/mol for the reaction catalyzed by malate dehydrogenase. Both of these reactions involve the oxidation of a secondary alcohol. Give an explanation as to why the oxidation of isocitrate is so exergonic.
8. How is succinate dehydrogenase unique when compared to the other enzymes in the citric acid cycle?
9. For a single rotation of the Krebs cycle, are the acetyl carbons that enter the citric acid cycle the exact same carbons that leave as CO2?