Electron transport chain

An electron transport chain is a series of membrane-associated carriers that pass electrons through redox reactions, conserving released energy by pumping protons or driving other energy-dependent processes.

Redox reaction: A chemical reaction in which electrons move from one substance to another. Each carrier passes electrons by alternating between oxidized and reduced states.
Oxidative phosphorylation: ATP production coupled to electron transport and the proton gradient it generates. The mitochondrial chain is the electron-transfer part of this broader ATP-producing process.
ATP synthase: A membrane enzyme that uses an ion gradient to synthesize ATP from ADP and phosphate. It converts the proton gradient generated by respiratory electron transport into ATP.
Mitochondrial electron transport chain: The series of respiratory complexes and mobile carriers in the mitochondrial inner membrane. It is the familiar eukaryotic example, but not the only kind of electron transport chain.
Proton-motive force: The electrochemical gradient of protons across a membrane, combining differences in concentration and electrical charge. Proton pumping stores the energy released by electron transfer as a usable gradient.
Electron carrier: A molecule or protein that accepts and donates electrons during chemical reactions. Chains are assembled from carriers whose redox states change in sequence.
Cellular respiration: The set of metabolic pathways by which cells extract energy from fuels and conserve it in ATP. Electron transport typically completes aerobic respiration by supporting most ATP synthesis.
Photosystem II: A light-absorbing protein complex that extracts electrons from water in oxygenic photosynthesis. It initiates photosynthetic electron flow by replacing lost electrons with those from water.
Chemiosmosis: The use of an ion gradient across a membrane to drive cellular processes, especially ATP synthesis. It explains how the proton gradient made by the chain can power ATP production.
Flavin adenine dinucleotide: A redox-active coenzyme that accepts electrons and protons in reactions such as succinate oxidation. Its reduced form feeds electrons into the mitochondrial chain through Complex II.

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