Question

Why does a single molecule of NADH result in the production of more ATP molecules than a single molecule of FADH₂ via oxidative phosphorylation?

1) NADH donates more electrons to the chain.
2) FADH₂ feeds its electrons into the electron transport chain further along the chain.
3) FADH₂ is less likely than NADH to participate in the electron transport chain.

Answer 1

NADH leads to more ATP production than FADH₂ because it starts donating electrons at the earlier Complex I in the ETC, enabling more protons to be pumped and a larger gradient for ATP synthesis. FADH₂ donates electrons later at Complex II, resulting in fewer ATPs produced.

Step-by-step explanation:

A single molecule of NADH results in the production of more ATP molecules than a single molecule of FADH₂ via oxidative phosphorylation because FADH₂ feeds its electrons into the electron transport chain (ETC) further along the chain. Specifically, NADH transfers electrons starting at Complex I, enabling more protons to be pumped across the mitochondrial membrane, which generates a larger proton gradient for ATP synthesis. In contrast, FADH₂ contributes electrons at Complex II, which pumps fewer protons and thus results in the production of fewer ATP molecules compared to NADH.

During glycolysis and the Krebs Cycle, NADH and FADH₂ are both produced. However, when they are oxidized in the ETC, NADH generates approximately three ATP molecules, whereas FADH₂ yields about two ATP molecules. This difference is due to where the two electron carriers enter the ETC and the subsequent proton pumping capability of each.