Chemiosmosis

Chemiosmosis is the movement of ions down an electrochemical gradient across a membrane, coupled to cellular work. In cells, proton flow through ATP synthase commonly drives ATP production.

Electrochemical gradient: A difference in ion concentration and electrical potential across a membrane. Its chemical and electrical components together store the energy that drives chemiosmosis.
Mitochondrion: A eukaryotic organelle where oxidative phosphorylation produces much of the cell's ATP. Its inner membrane supports respiratory proton gradients and ATP synthesis.
Peter Mitchell: The British biochemist who proposed the chemiosmotic hypothesis in 1961. His proposal replaced direct chemical coupling as the explanation for oxidative phosphorylation.
Substrate-level phosphorylation: ATP formation by direct transfer of a phosphate group from a metabolic intermediate to ADP. It makes ATP without an ion gradient or membrane-bound ATP synthase.
Proton motive force: The energy stored in a transmembrane proton gradient and voltage difference. It is the electrochemical gradient most commonly harnessed by cellular chemiosmosis.
Chloroplast: A photosynthetic organelle that converts light energy into chemical energy. Its thylakoid membrane uses a proton gradient to drive ATP synthesis.
Chemiosmotic hypothesis: The proposal that electron transport builds a transmembrane proton gradient that drives ATP synthesis. It states the central explanatory claim behind chemiosmosis in energy conversion.
Chemical coupling hypothesis: The historical proposal that high-energy chemical intermediates directly link electron transport to ATP synthesis. It was the principal alternative to Mitchell's gradient-based account of oxidative phosphorylation.
ATP synthase: A membrane protein complex that uses ion flow to synthesize ATP. Protons flowing through this enzyme couple gradient dissipation to ATP production.
Photophosphorylation: ATP synthesis powered by light-driven electron transport and a proton gradient. It demonstrates chemiosmotic coupling in photosynthesis rather than respiration.

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