Question

Why does NADH have a higher metabolic efficiency than FADH2? My professor said something about NADH being included in the proton pumps? Is that why? How does this connect to the P to O ratio?

Answer 1

NADH produces 3 ATP during the ETC (Electron Transport Chain) with oxidative phosphorylation and FADH₂ produces 2 ATP in the same procedure.

NADH is very good at doner of electrons in redox reactions and its electrons are at a high energy level, Hence it gives up its electron directly to Complex I to form NAD⁺. Complex I is at a higher energy level than the other Complexes. Complex I transfers the electron to Complex III and energy is given off to pump protons across the membrane and a gradientis created. The electron moves again to Complex IV and again pumps more electrons across the membrane. Because NADH started with Complex I, it had more chances to pumps more protons across the gradient, which powers the ATP synthase and gives us 3 ATP per molecule of NADH.

FADH₂ gives up its electron to Complex II, as it is not as good electron doner as NADH. Complex II does not pump proton accross the membrane, so less protons have been pumped by the time Complex IV is formed, hence 2 ATP per molecule of FADH₂ is produced.