Pyruvate Dehydrogenase (PDH)

1. Fill in the table to summarize the functions of the enzymes and coenzymes in PDH. E₁ requires only one coenzyme. E₂ and E₃ each require two coenzymes.
Write P or C in the enzyme column to indicate whether the coenzyme listed is a prosthetic group (P) or a co-substrate (C)

2. Allosteric regulation of PDH is determined by the following ratios:
NADH,    AcCoA , and   ATP .
  NAD⁺    CoA-SH          AMP
a. For each ratio, which molecule inhibits?
b. Which ratio primarily reflects energy supply for the cell?
c. Which ratio primarily indicates oxygen supply for the cell?
d. Which two ratios indicate the rate of citric acid cycle function?

3. Contrast covalent regulation of PDH with covalent regulation of PFK-2/FBPase-2 by filling in the table below.

4. What is the advantage to a cell of covalently modifying PDH?

5. What is the net energy yield per glucose of glycolysis + modifying 2 pyruvates by PDH?

6. Fermentation uses pyruvate as the final e⁻ acceptor to recycle the NADH produced during glycolysis. Why isn't AcCoA used instead of pyruvate?

7. Add pyruvate, its intermediates, and its products to the diagram below. You should have 3 intermediates, 2 products from pyruvate, and 1 additional product.

Citric Acid Cycle

1. Which reactions of the citric acid cycle involve a condensation reaction and an isomerization reaction?
Draw the substrate(s) and product(s) of each reaction and name any coenzyme that is required.

2. Which reactions of the citric acid cycle involve oxidative decarboxylation?
Draw the substrate and product of each of these reactions. Which coenzyme is required?

3. How does α-ketoglutarate dehydrogenase resemble pyruvate dehydrogenase?
a. Draw both substrates and emphasize their similarities.
b. Do the same with the products.
c. What would you have to change in your answer to question 7 for PDH in order to
        show the reaction catalyzed by α-ketoglutarate dehydrogenase?

4. Which reaction of the citric acid cycle involves substrate level phosphorylation?
a. Write the overall reaction and name the enzyme.
b. The reaction occurs in 3 steps. Write the steps of the reaction.

5. Which reactions of the citric acid cycle involve the following sequence of reactions:
oxidation, hydration, oxidation?
Draw the four molecules involved in the reaction sequence and name any coenzyme that is required.

6. Oxaloacetate + 2 H⁺ + 2 e⁻ → malate                E°′ = − 0.166 V
NAD⁺ + 2 H⁺ + 2 e⁻ → NADH + H⁺               E°′ = − 0.320 V
a. Write the coupled whole reaction.    b. Calculate ΔE°′.
c. Using the equation ΔG°′ = − n F ΔE°′, calculate ΔG°′. F = 96480 J/V-mole

7. The molecules below are shown in the order in which they occur in the citric acid cycle. Identify the molecules shown and draw the structures of the three missing molecules.

8. What is the net energy per glucose degraded by glycolysis, PDH, and the citric acid cycle? Your answer should be in numbers of ATP (including GTP), NADH, and FADH₂ .

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