Question

ytoplasmic malate is a substrate for the malic enzyme in the following reaction malate + NAD+ ⟶ pyruvate + CO2 + NADH + H+ Use Malate as the sole energy source. Assume a fully functional TCA cycle and Electron Transport Chain. How many ATP could be produced by each Malate? Show work.

Answer 1

Okay, remember that the ETC takes NADH and FADH as fuel for ATP production, and TCA cycle takes acetyl-CoA as fuel. Pyruvate needs the intermediate reaction to be transformed into acetyl-CoA, this reaction produces another molecule of NADH.

Okay, we already have 2 NADH from the malic enzyme reaction and from the intermediate reaction.

The TCA cycle forms 3 NADH, 1 FADH and 1 GTP per acetyl CoA molecule.

For the ETC, we have 2 NADH from the first two reactions, then 3 NADH from TCA cycle and 1 FADH. This chain is going to yield 3 ATP per NADH molecule and 2 ATP per FADH molecule, that is 3(5) = 15 and 1(2) = 2. The five NADH molecules produce 15 ATP and the FADH produces 2 ATP.

The final energy yield is then 17 ATP molecules and 1 GTP molecule, that is per malate molecule.