What is the approximate ATP yield per NADH and per FADH2 in oxidative phosphorylation, and how many protons are pumped per NADH?

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Multiple Choice

What is the approximate ATP yield per NADH and per FADH2 in oxidative phosphorylation, and how many protons are pumped per NADH?

In oxidative phosphorylation, the amount of ATP produced depends on how many protons are pumped across the inner mitochondrial membrane and how many protons are needed to make one ATP. NADH donates its electrons to Complex I, which pumps about 4 protons. The electrons then move through Complex III (about 4 more protons) and Complex IV (about 2 more), giving a total of roughly 10 protons pumped per NADH. FADH2 enters at Complex II, which does not pump protons, so only Complex III and Complex IV contribute (about 4 plus 2 protons), totaling around 6 protons per FADH2. The ATP synthase typically uses about 4 protons to make one ATP (roughly 3 for the rotor’s phosphorylation steps plus 1 for transporting phosphate), so the ATP yield from NADH is about 10 protons / 4 protons per ATP ≈ 2.5 ATP, and from FADH2 is about 6 protons / 4 protons per ATP ≈ 1.5 ATP. Thus, the best answer is: NADH ≈ 2.5 ATP; FADH2 ≈ 1.5 ATP; ~10 protons pumped per NADH.

In oxidative phosphorylation, the amount of ATP produced depends on how many protons are pumped across the inner mitochondrial membrane and how many protons are needed to make one ATP. NADH donates its electrons to Complex I, which pumps about 4 protons. The electrons then move through Complex III (about 4 more protons) and Complex IV (about 2 more), giving a total of roughly 10 protons pumped per NADH. FADH2 enters at Complex II, which does not pump protons, so only Complex III and Complex IV contribute (about 4 plus 2 protons), totaling around 6 protons per FADH2.

The ATP synthase typically uses about 4 protons to make one ATP (roughly 3 for the rotor’s phosphorylation steps plus 1 for transporting phosphate), so the ATP yield from NADH is about 10 protons / 4 protons per ATP ≈ 2.5 ATP, and from FADH2 is about 6 protons / 4 protons per ATP ≈ 1.5 ATP.

Thus, the best answer is: NADH ≈ 2.5 ATP; FADH2 ≈ 1.5 ATP; ~10 protons pumped per NADH.

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