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The ElectronTransport Chain

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The enymes and electron carriers neededfor the !T" are located along the inner

mitochondrial membrane. #ithin this membraneare four distinct protein complexes$ eachcontaining some of the molecules needed for the!T" process to occur. These four protein

complexes$ which are tightly bound to themembrane$ are

"omplex %& NADH'coenyme ( reductase

"omplex %%& )uccinate'coenyme ( reductase"omplex %%%& "oenyme ('cytochrome c reductase"omplex %*& "ytochrome c oxidase

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Complex I:NADHCoenzyme Q

Reductase

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The next steps in+ol+e transfer of electronsfrom the reduced F0NH2 through a series ofiron4sulfur proteins /Fe)s1.

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%n the 3nal complex % reaction$ Fe/%%1) isrecon+erted into Fe/%%%1) as each of twoFe/%%1) units passes an electron to "o($ changingit from its oxidied form /"o(1 to its reducedform /"o(H21.

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Complex II:uccinateCoenzyme Q

Reductase

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"omplex %%$ which is much smaller thancomplex %$ contains only , subunits$ including twoFe)s. This complex is used to process the FADH2that is generated in the citric acid cycle whensuccinate is con+erted to fumarate.

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"omplex %%% contains 55 different subunits.!lectron carriers present include se+eral iron'sulfur proteins as well as se+eral cytochromes.

A cytochromeis a heme6containing protein inwhich re+ersible oxidation and reduction of an ironatom occur.

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The initial substrate for complex %%% is"o(H2 molecules carrying the electrons that ha+ebeen processed through complex % /from NADH1and also those processed through complex %%/from FADH21. The electron transfer processproceeds from "o(H2 to an Fe)$ then to cyt b$

then to another Fe)$ then to cyt c5$ and 3nally tocyt c. "yt c can mo+e laterally in theintermembrane space8 it deli+ers its electrons tocomplex %*.

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Complex I!:Cytochrome c "xidase

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"omplex %* contains 57 subunits$ including

two cytochromes. The electron mo+ement owsfrom cyt c to cyt a to cyt a7.

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