Chapter 10, Problem 10.6PS

QUANTITATIVE The Calculating Cell Biologist. Use Table 10-2 as the basis for the calculations needed to answer the following questions.

1. (a) Without doing any calculations initially, predict whether isocitrate can pass electrons exergonically to NAD⁺ under standard conditions. Why do you predict that?
2. (b) What is the $\Delta {E^{\prime }}_0$ for the oxidation of isocitrate by NAD⁺ under standard conditions? Does this calculation support the prediction you made in part a? Explain your answer.
3. (c) Calculate the $\Delta G{°}^{\prime }$ for the oxidation of isocitrate by NAD⁺ under standard conditions. In what way is this calculation relevant to aerobic energy metabolism?
4. (d) Repeat parts a–c for the oxidation of lactate to pyruvate by NAD⁺. In what way is this calculation relevant to aerobic energy metabolism?
5. (e) Now repeat parts a–c for the oxidation of succinate to fumarate with NAD⁺ as the electron acceptor. You should find that the $\Delta G{°}^{\prime }$ is highly positive. What does this tell us about the likelihood that NAD⁺ could serve as the electron acceptor for the succinate dehydrogenase reaction of the citric acid cycle?
6. (f) Finally, repeat parts a–c for the oxidation of succinate to fumarate with coenzyme Q as the electron acceptor. Why does it make sense to regard coenzyme Q as the electron acceptor when succinate dehydrogenase is shown in Figure 10-9 with FAD as the immediate electron acceptor?