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Electron transport chain

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Electron transfer chains (ETC) are the cellular mechanisms used for extracting energy from sunlight in photosynthesis and also from redox reactions, such as the oxidation of sugars in cellular respiration.

In aerobic respiration, each molecule of glucose leads to about 34 molecules of ATP being produced by the ETC. This is by far the most productive part of respiration.[1]


The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the free energy (energy available to do work) of the reactants and products. Any reaction that decreases the overall free energy of a system will happen.

ATP synthase, an enzyme found among all domains of life, is powered by a transmembrane proton electrochemical gradient. This is the result of a series of redox reactions.[2] The function of the electron transport chain is to produce this gradient.[3][4] The free energy is used to drive ATP synthesis.


  1. Rich P.R. 2003. The molecular machinery of Keilin's respiratory chain. Biochemical Society Transactions 31 (pt 6): 1095–1105. doi:10.1042/BST0311095 PMID 14641005
  2. Karp, Gerald (2008). Cell and molecular biology, 5th ed. Hoboken NJ: Wiley. pp. 194. ISBN 10-0-470-04217-6 .
  3. Murray, Robert K.; Daryl K. Granner, Peter A. Mayes, Victor W. Rodwell (2003). Harper's Illustrated Biochemistry. New York, NY: Lange Medical Books/ McGraw Hill. pp. 96. ISBN 0-07-121766-5 .
  4. Harper's Illustrated Biochemistry explaining the function of the complexes of the transport chain: "Each of the respiratory chain complexes I, II, and IV... acts as a proton pump...creating an electrochemical potential difference across the [mitochondrial inner] membrane".(96)