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An electron transport chain (ETC [1]) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H + ions) across a membrane.
The chain of redox reactions driving the flow of electrons through the electron transport chain, from electron donors such as NADH to electron acceptors such as oxygen and hydrogen (protons), is an exergonic process – it releases energy, whereas the synthesis of ATP is an endergonic process, which requires an input of energy.
The coenzyme Q : cytochrome c – oxidoreductase, sometimes called the cytochrome bc 1 complex, and at other times complex III, is the third complex in the electron transport chain (EC 1.10.2.2), playing a critical role in biochemical generation of ATP (oxidative phosphorylation).
Over 30 different nuclear-encoded chaperone proteins are required for COX assembly. [12] Cofactors, including hemes, are inserted into subunits I & II. The two heme molecules reside in subunit I, helping with transport to subunit II where two copper molecules aid with the continued transfer of electrons. [13] Subunits I and IV initiate assembly.
An electron transfer flavoprotein (ETF) or electron transfer flavoprotein complex (CETF) is a flavoprotein located on the matrix face of the inner mitochondrial membrane and functions as a specific electron acceptor for primary dehydrogenases, transferring the electrons to terminal respiratory systems such as electron-transferring-flavoprotein dehydrogenase.
The cellular location of cytochromes depends on their function. They can be found as globular proteins and membrane proteins. In the process of oxidative phosphorylation, a globular cytochrome cc protein is involved in the electron transfer from the membrane-bound complex III to complex IV. Complex III itself is composed of several subunits ...
The high reduction potential of the N2 cluster and the relative proximity of the other clusters in the chain enable efficient electron transfer over long distance in the protein (with transfer rates from NADH to N2 iron-sulfur cluster of about 100 μs). [12] [13] The equilibrium dynamics of Complex I are primarily driven by the quinone redox cycle.
In addition, the reoxidation of the 'FeS protein' releases the proton bound to His181 into the intermembrane space. The other electron, which was transferred to the b L heme, is used to reduce the b H heme, which in turn transfers the electron to the ubiquinone bound at the Q i site. The movement of this electron is energetically unfavourable ...