Electron Transport Chain (ETC) & Oxidative Phosphorylation
| Cellular Location: | Inner Mitochondrial Membrane (Impermeable to ions) |
| Proton Pumping Sites: | Complex I (4H+), Complex III (4H+), Complex IV (2H+) |
| ATP Synthase Mechanics: | Complex V (F0 subunit spans membrane; F1 subunit catalyzes ATP) |
| Final Electron Acceptor: | Oxygen (O2) (Reduced to H2O at Complex IV) |
High-Yield Core Realities:
- Complex II Entry Trap: FADH2 enters exclusively via Succinate Dehydrogenase (Complex II). Complex II pumps zero protons, which is why FADH2 yields less ATP (~1.5) than NADH (~2.5).
- Mobile Electron Carriers: Coenzyme Q (Ubiquinone) is lipid-soluble and shuttles electrons from Complexes I and II to III. Cytochrome c is water-soluble (peripheral membrane protein) and shuttles them from III to IV.
- ETC Inhibitors (Block Electron Flow):• Complex I: Rotenone, Amobarbital (Amytal), Piericidin A.
• Complex III: Antimycin A.
• Complex IV: Cyanide (CN-), Carbon Monoxide (CO), Azide. (Bind ferric/ferrous iron in cytochrome a3).
- Uncouplers (Dissipate Proton Gradient): 2,4-Dinitrophenol (DNP), Aspirin (salicylate overdose), and endogenous Thermogenin (UCP1) in brown fat. They leak H+ back into the matrix, stopping ATP synthesis while increasing O2 consumption and generating heat.
- Complex V Inhibitor: Oligomycin binds the F0 subunit directly, closing the proton channel and completely halting oxidative phosphorylation.