Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 11

Oxidation of Cytosolic NADH. Insome eukaryotic cells, the NADH generated by glycolysis in the cytosol is reoxidized by the glycerol phosphate shuttle shown in Figure 10-23.
(a)Write balanced reactions for the reduction of dihydroxyace- tone phosphate (DHAP)to glycerol-3-phosphate (glycerol-3-P)by cytosolic NADH and for the oxidation of glycerol-3-P to DHAP by the FAD-linked glycerol-3-P dehydrogenase in the inner membrane of the mitochondrion.
(b)Add the two reactions in part a to obtain a summary reaction for the transfer of electrons from cytosolic NADH to mitochondrial FAD. Calculate
and
for this reaction. Is the inward movement of electrons thermodynamically feasible under standard conditions
(c)Write a balanced reaction for the reoxidation of FADH 2 by coenzyme Q within the inner membrane, assuming that CoQ is reduced to CoQH 2. Calculate
and
for this reaction. Is this transfer thermodynamically feasible under standard conditions
(d)Write a balanced reaction for the transfer of electrons from cytosolic NADH to mitochondrial CoQ, and calculate
and
for this reaction. Is this transfer thermodynamically feasible under standard conditions
(e)Assume that the [NADH]/[NAD + ] ratio in the cytosol is 5.0 and that the [CoQH 2 ]/[CoQ] ratio in the inner membrane is 2.0. What is
for the reaction in part d at 25°C and pH 7.0
(f)Is
for the inward transfer of electrons from NADH to CoQ affected by the ratio of the reduced to the oxidized forms of the enzyme-bound FAD in the inner membrane Why or why not