. Principles of modern biology. Biology. TPN and DPN Pyridine Acceptors FAD and FMN Flavin Acceptors Primary Acceptor Compounds. Cytochrome b Ubiquinone Cytochrome c Cytochrome a Cytochrome System in Mitochondria Cytochrome Oxidase Oxygen Fig. 8-4. Electron-hydrogen transmission during oxidative phosphorylation. Each time an electron (and hydro- gen) passes from higher to lower level, the oxidation energy is conserved and stored—mainly in the form of high-energy phosphate (ATP). cell (Fig. 8-4). At the very end, of course, the electron-hydrogen pairs are passed on to oxygen, forming water as t
. Principles of modern biology. Biology. TPN and DPN Pyridine Acceptors FAD and FMN Flavin Acceptors Primary Acceptor Compounds. Cytochrome b Ubiquinone Cytochrome c Cytochrome a Cytochrome System in Mitochondria Cytochrome Oxidase Oxygen Fig. 8-4. Electron-hydrogen transmission during oxidative phosphorylation. Each time an electron (and hydro- gen) passes from higher to lower level, the oxidation energy is conserved and stored—mainly in the form of high-energy phosphate (ATP). cell (Fig. 8-4). At the very end, of course, the electron-hydrogen pairs are passed on to oxygen, forming water as the end product. This final direct oxidation cannot occur, however, in the absence of another enzyme,2 cytochrome oxidase (Fig. 8-4). It is difficult to see how such an orderly electron transmission system could operate unless the component enzymes were built into the structure of the cell in a very pre- cisely patterned fashion. Therefore it is not 2 Cytochrome oxidase is extremely sensitive to in- activation by cyanide (CAT) compounds. This sen- sitivity accounts for the remarkable potency of cyanide poisons in inducing death by asphyxiation in cells and organisms generally. surprising to find that the cytochrome system and some of the other enzymes are localized in the mitochondria, presumably at fixed po- sitions in the internal membranes of these complex structures (p. 27). Mitochondria pre- pared from disrupted cells—or even frag- ments of mitochondria—can still carry on oxidative phosphorylation, under the proper conditions. Such a preparation will continue to utilize oxygen and to build up ATP if provided with DPN • H2 (as an electron-hy- drogen source), plus ADP and inorganic phosphate. In essence the nature of the electron trans- fer process can be understood when it is realized that the cytochrome enzymes are. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance o
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