Bioenergetics

Why this matters

Two of the drugs you will prescribe most often work by redox chemistry: metronidazole is activated only by organisms whose electron carriers sit at a low enough potential, and nitrous oxide oxidises a cobalt atom it should have left alone. Tooth whitening is radical chemistry with a legal concentration limit. And the disease that proves reactive oxygen species are protective rather than merely destructive announces itself as severe periodontitis in a child.

The big picture

Electrons fall from carriers that hold them loosely to oxygen, which holds them tightly. The energy released is not captured as heat but used to push protons across a membrane, and the protons falling back through one rotary enzyme make ATP. Every part of that sentence is measurable, and the whole of metabolism hangs off it.

The 14 cards in this lesson

1. 01What decides whether a reaction runs
2. 02Nothing is stored in a phosphate bond
3. 03Coupling needs a shared intermediate
4. 04Oxidation when no electron obviously moves
5. 05The carriers, and what each is for
6. 06The electron tower
7. 07The one calculation worth doing yourself
8. 08The chain, complex by complex
9. 09Chemiosmosis: protons do the carrying
10. 10The organelle built for the job
11. 11Clinical alert — in the lesson
12. 12Reactive oxygen species and the defences
13. 13The disease that proves radicals are protective
14. 14Clinical alert — in the lesson

You have got it when

You are ready to continue when you can explain why nothing is stored in a phosphate bond, work out the free energy available from NADH using the redox potentials, and say why metronidazole kills anaerobes and leaves your own cells alone.