Chapter 18 Biochemistry6e

Chapter 18 Biochemistry6e - Chapter 18 Biochemistry...

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Chapter 18 Biochemistry Oxidative Phosphorylation-6th Edition by Berg, Tymoczko and Stryer Oxidative phosphorylation is the process in which electrons from either NADH or FADH 2 are transferred to O 2 via a series of electron carriers and, as a result of the transfer of electrons, ATP is created . While this definition is true in animal and plant cells, a number of microbes may substitute electron acceptors other than O 2 to act as the electron accepting sink for the transfer of electrons. In eukaryotes, the mitochondrion is the site of oxidative phosphorylation while it is the prokaryote cell membrane in Bacteria and Archaea . While oxidative phosphorylation is not a very complicated concept, the actual details and mechanics of it are. The movement of electrons from either NADH or FADH 2 results in the pumping of H + s across either the mitochondrial inner membrane or the bacterial membrane and creates a unequal distribution of both H + s and electrical charge across the membranes known as a proton-motive force. The flow of protons, through an enzyme complex, either back into the mitochondrial matrix or the bacterial cell results in ATP being formed. In this respect, the oxidation of fuel molecules is coupled to the generation of ATP via the re-entry of H + s through the enzyme complex, otherwise known as the ATP synthetase or ATPase (Show Figure 18.1) . Cellular respiration , or simply respiration , is the process by which food molecules are oxidized to generate energy-rich compounds such as NADH or FADH 2 which are used to generate the proton- motive force, from which phosphoryl transfer potential energy (ATP) is created. There are three H + pumping sites, or proton pumps , in the electron transport chain or series of electron carriers that deliver electrons to oxygen from either NADH or FADH 2 . They are 1-NADH-Q oxidoreductase, 2-Q- 1
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cytochrome c oxidoreductase and 3-cytochrome oxidase ( Show Figure 18.6 ). All three are large oxidation-reduction centers in which a number of electron carrying components (Fe-S clusters, hemes, Cu ions, flavins, quinones) may be present. The flow of protons across the cell membrane, the last step in the generation of ATP via oxidative phosphorylation, is thus an inter-convertible way of energy conservation (free energy) in biological systems. The Mitochondrion is the Site of Oxidative Phosphorylation in Eukaryotes The mitochondrion is the site of the Krebs Cycle enzymes , the electron transport assembly and of the enzymes of fatty acid oxidation , which will be discussed later in the course. To refresh, the mitochondrion consists of an outer membrane , a highly folded inner membrane that gives rise to the cristae and the plasm that occupies the space inside the cristae , known as the matrix (Show Figure 18.2) . There is also the space occupied between the inner and outer membranes, simply known as the inter-membrane space . The matrix is the site of most of the enzymes and reactions of the Krebs Cycle and fatty acid oxidation
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This note was uploaded on 04/26/2008 for the course CHEM 361 taught by Professor Defreitas during the Spring '08 term at Loyola Chicago.

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Chapter 18 Biochemistry6e - Chapter 18 Biochemistry...

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