Electron transport chain

An electron transport chain (ETC) is a series of <a href="/facts/Protein_complex/GW11Ee34">protein complexes</a> and other molecules which <a href="/facts/Electron_transfer/BIdASS9R">transfer</a> <a href="/facts/Electron/L0KBo5cW">electrons</a> from <a href="/facts/Electron_donor/7JxwwW43">electron donors</a> to <a href="/facts/Electron_acceptor/sRvhMXqH">electron acceptors</a> via <a href="/facts/Redox/Pyd5RVcj">redox</a> reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of <a href="/facts/Proton/clCjepXP">protons</a> (H+ ions) across a <a href="/facts/Biological_membrane/ljBsfK4r">membrane</a>. Many of the <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> in the electron transport chain are embedded within the <a href="/facts/Membrane/FDlaJe23">membrane</a>.
The flow of electrons through the electron transport chain is an <a href="/facts/Exergonic_process/2kPJobE7">exergonic process</a>. The energy from the redox reactions creates an <a href="/facts/Electrochemical_gradient/IEfjjoIL">electrochemical proton gradient</a> that drives the synthesis of <a href="/facts/Adenosine_triphosphate/nB9bwgcU">adenosine triphosphate</a> (ATP). In <a href="/facts/Cellular_respiration/kb6gpsvL">aerobic respiration</a>, the flow of electrons terminates with molecular <a href="/facts/Oxygen/acyn6o8r">oxygen</a> as the final electron acceptor. In <a href="/facts/Anaerobic_respiration/IMSY03HG">anaerobic respiration</a>, other electron acceptors are used, such as <a href="/facts/Sulfate/yuWVxsUf">sulfate</a>.
In an electron transport chain, the redox reactions are driven by the difference in the <a href="/facts/Gibbs_free_energy/bvenDuzh">Gibbs free energy</a> of reactants and products. The free energy released when a higher-energy electron donor and acceptor convert to lower-energy products, while electrons are transferred from a lower to a higher <a href="/facts/Redox_potential/PqpNUgSl">redox potential</a>, is used by the complexes in the electron transport chain to create an electrochemical gradient of ions. It is this electrochemical gradient that drives the synthesis of ATP via coupling with <a href="/facts/Oxidative_phosphorylation/en2l08P9">oxidative phosphorylation</a> with <a href="/facts/ATP_synthase/5NBMxsVX">ATP synthase</a>.
In <a href="/facts/Eukaryotes/SkwyPLMA">eukaryotic organisms</a>, the electron transport chain, and site of <a href="/facts/Oxidative_phosphorylation/en2l08P9">oxidative phosphorylation</a>, is found on the <a href="/facts/Inner_mitochondrial_membrane/IJIE4o0h">inner mitochondrial membrane</a>. The energy released by reactions of oxygen and reduced compounds such as <a href="/facts/Cytochrome/VF51IeGv">cytochrome</a> c and (indirectly) <a href="/facts/Nicotinamide_adenine_dinucleotide/BHdLW925">NADH</a> and <a href="/facts/Flavin_adenine_dinucleotide/uzADx3ES">FADH2</a> is used by the electron transport chain to pump protons into the <a href="/facts/Intermembrane_space/lEt0NyqY">intermembrane space</a>, generating the <a href="/facts/Electrochemical_gradient/IEfjjoIL">electrochemical gradient</a> over the inner <a href="/facts/Mitochondrial_membrane/ErHqrdJ1">mitochondrial membrane</a>. In <a href="/facts/Photosynthesis/TMV7w693">photosynthetic</a> eukaryotes, the electron transport chain is found on the <a href="/facts/Thylakoid/d9PEe649">thylakoid</a> membrane. Here, light energy drives electron transport through a <a href="/facts/Proton_pump/mMzXv8P3">proton pump</a> and the resulting proton gradient causes subsequent synthesis of ATP. In <a href="/facts/Bacteria/wC8xSCsU">bacteria</a>, the electron transport chain can vary between species but it always constitutes a set of redox reactions that are coupled to the synthesis of ATP through the generation of an electrochemical gradient and oxidative phosphorylation through ATP synthase.

Electron transport chain open-in-new

Electron transport chain