Question

Net energy gain from malic acid and succinic acid are
Malic acid: 3

Succinic acid: 5.

Justify the mentioned values.

Answer 1

The net gain of energy can be explained by referring the Kreb's cycle where both the compounds are intermediates :

Alpha-Keto Glutaric acid gives succinic acid which further transforms to malic acid giving a molecule of FADH${}_2$ . While malic acid further converts to Oxalo-Acetic Acid giving a high energy bonded molecule NADH + H${}^{+}$. As we know, both the compounds NADH+H${}^{+}$ and FADH${}_2$ after entering to electron transport system gives out 3 ATP and 2 ATP respectively.

Thus after full oxidation of succinic acid, we get 1 FADH${}_2$ and a molecule of NADH+H${}^{+}$ = 5 ATP by ETS and malic acid give 1 NADH+H${}^{+}$ = 3ATP.