NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately
reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Why is more ATP made per molecule of NADH than per molecule of FADH2?
NADH and FADH2 are both electron carriers of the electron transport chain. NADH gives up its electrons starting from Complex I, which has a higher energy level compared to other complexes. Energy is given off to pump protons across the membrane by the time electrons are transferred to ComplexIII. More electrons are pumped across the membrane as electrons move to Complex IV. Because NADH commenced giving up its electrons from Complex I (higher energy level complex), more protons are pumped across the membrane gradient, which enables ATP synthase with more power to produce 3ATP molecules per NADH molecule.
On the other hand, 2 molecules of ATP are generated by FADH2 because it starts by giving up its electrons to ComplexII. It missed a chance to pump protons across the membrane when it passed Complex I. By the time the electrons reach Complex IV, less protons have been pumped. The lesser the protons to power ATP synthase, the lesser the ATP molecules produced.
