Expansion
Electrons pass down the chain, pumping protons that drive ATP synthase
Expansion
On the inner mitochondrial membrane:
- NADH donates electrons at complex I, FADH2 at complex II
- Electrons pass through complexes I, III and IV via ubiquinone and cytochrome c
- Energy released pumps protons into the intermembrane space, creating an electrochemical gradient
- Protons flow back through ATP synthase (complex V), driving ATP synthesis: chemiosmosis
- Oxygen is the final electron acceptor, forming water
Yield: about 2.5 ATP per NADH and 1.5 per FADH2, so about 26 ATP per glucose.
Poisons localise neatly:
- Complex I: rotenone
- Complex III: antimycin
- Complex IV: cyanide, carbon monoxide, hydrogen sulphide
- ATP synthase: oligomycin
- Uncouplers (dinitrophenol, and physiologically thermogenin in brown fat): allow protons to leak back, so energy is released as heat rather than ATP
Cyanide poisoning gives a characteristically high venous oxygen saturation with severe lactic acidosis, since tissues cannot extract oxygen.