Chapter 20

In problem 18 at the end of Chapter \(19,\) you might have calculated the number of molecules of oxaloacetate in a typical mitochondrion. What about protons? A typical mitochondrion can be thought of as a cylinder \(1 \mu \mathrm{m}\) in diameter and \(2 \mu \mathrm{m}\) in length. If the \(\mathrm{pH}\) in the matrix is \(7.8,\) how many protons are contained in the mitochondrial matrix?

Considering that all other dehydrogenases of glycolysis and the TCA cycle use NADH as the electron donor, why does succinate dehydrogenase, a component of the TCA cycle and the electron transfer chain, use FAD as the electron acceptor from succinate, rather than \(\mathrm{NAD}^{+}\) ? Note that there are two justifications for the choice of FAD here-one based on energetics and one based on the mechanism of electron transfer for FAD versus \(\mathrm{NAD}^{+}\).

Based on your reading on the \(\mathrm{F}_{1} \mathrm{F}_{0}\) -ATPase, what would you conclude about the mechanism of ATP synthesis: a. The reaction proceeds by nucleophilic substitution via the \(S_{N} 2\) mechanism. b. The reaction proceeds by nucleophilic substitution via the \(\mathrm{S}_{\mathrm{N}} 1\) mechanism. c. The reaction proceeds by electrophilic substitution via the \(\mathrm{E} 1\) mechanism. d. The reaction proceeds by electrophilic substitution via the \(\mathrm{E} 2\) mechanism.

Imagine that you are working with isolated mitochondria and you manage to double the ratio of protons outside to protons inside. In order to maintain the overall \(\Delta G\) at its original value (whatever it is), how would you have to change the mitochondria membrane potential?