Electron transport and the ATP ledger
Proton pumping across the four complexes: 4, 0, 4, 2.
| Complex | Name | Pumps | Accepts from | Note |
|---|---|---|---|---|
| I | NADH dehydrogenase | 4 H⁺ | NADH | Entry point for all NADH. Blocked by rotenone. |
| II | Succinate dehydrogenase | 0 H⁺ | FADH₂ | An entry point for electrons, with no proton pumping. This is why FADH₂ yields less ATP than NADH. |
| III | Cytochrome bc₁ complex | 4 H⁺ | QH₂ | Blocked by antimycin A. |
| IV | Cytochrome c oxidase | 2 H⁺ | cytochrome c | Reduces O₂ to water. Blocked by cyanide, carbon monoxide and azide. |
Where the carriers come from, per glucose
| Source | NADH | FADH₂ | Direct | |
|---|---|---|---|---|
| Glycolysis | 2 | 0 | 2 ATP | 2 ATP substrate-level |
| Pyruvate dehydrogenase | 2 | 0 | 0 | None |
| TCA cycle (×2 turns) | 6 | 2 | 2 ATP | 2 GTP |
| Total | 10 | 2 | 4 ATP | 10 × 2.5 + 2 × 1.5 = 28 from the chain, plus 4 direct |
Shuttles: why the total is 30 or 32
| Shuttle | Tissue | Delivers as | Per glucose | Note |
|---|---|---|---|---|
| Malate-aspartate | Liver, heart | NADH | 32 ATP | Cytosolic NADH arrives as NADH, worth 2.5 ATP each. |
| Glycerol-3-phosphate | Muscle, brain | FADH₂ | 30 ATP | Cytosolic NADH arrives as FADH₂, worth 1.5 ATP each. |
The two NADH from glycolysis are cytosolic and cannot cross the inner membrane alone. The shuttle used decides the final number.