Oxidative phosphorylation
Electrons roll downhill to oxygen; the proton gradient pays for ATP.
Per NADH: 10 H⁺ pumped → ~2.5 ATP · per FADH₂: 6 H⁺ → ~1.5 ATP
This mnemonic, unpacked word by word →
Two coupled machines. Complexes I, III and IV pump protons as electrons fall toward O₂; ATP synthase lets them back in and phosphorylates ADP. Inhibitors stop the flow; uncouplers drain the gradient as heat while O₂ consumption races. That opposite effect on O₂ use is how you tell them apart.
Entry point for matrix NADH, from pyruvate dehydrogenase, the TCA cycle, and glycolysis when the malate-aspartate shuttle delivers it. The glycerol-3-phosphate shuttle bypasses Complex I entirely, which is the 30-vs-32 story. Blocked by rotenone: Roten-ONE inhibits Complex ONE.
The same enzyme as TCA step 6, a side entrance that pumps no protons, like DHAP joining glycolysis. Skipping Complex I’s four protons is why FADH₂ is worth 1.5 ATP, and NADH 2.5. Blocked by malonate: "Karl Malone-ate blocks Complex two."
The Q cycle hands electrons one at a time to cytochrome c, a small mobile protein on the outer face of the inner membrane. Blocked by antimycin A.
The only place the oxygen you breathe is consumed: O₂ is the final electron acceptor. Blocked by cyanide, carbon monoxide and azide, which is why these poisons kill with plenty of O₂ in the blood.
Roughly 4 H⁺ per ATP (3 through the rotor, 1 to import Pᵢ): 10/4 ≈ 2.5 and 6/4 = 1.5. Blocked by oligomycin. Uncouplers, 2,4-DNP, aspirin overdose, thermogenin (UCP1) in brown fat, bypass it entirely: the gradient leaks away as heat, electron transport and O₂ use speed up, and no ATP is made. The whole chain otherwise runs at the pace ADP allows (respiratory control).