8885_c19_690-7503/1/0411:32 AM Page690mac76mac76:385-z: chaptar 19 OXIDATIVE PHOSPHORYLATION AND PHOTOPHOSPHORYLATION OXIDATIVE PHOSPHORYLATION 19.1 Electron-Transfer Reactions in Mitochondria 691 yielding metabolism in aerobic organisms. All oxi 19.2 ATP Synthesis 704 dative steps in the degradatic hydrates, fats, and amino acids conve llul 19.3 Regulation of Oxidative Phosphorylation 716 respiration, in which th es the 19.4 Mitochondrial Genes: Their Origin and the Effects synthesis of ATP. P of Mutations 719 by which phot 19.5 The Role of Mitochondria in Apoptosis and of sunlight- Oxidative Stress 721 sphere-and h tive phosp PHOTOSYNTHESIS: HARVESTING LIGHT ENERGY for most of t of the time 19.6 General Features of Photophosphorylation 723 occurs in 19.7 Light Absorption 725 iIn euka plasts Oxidative 19.8 The Central Photochemical Event: Light-Driven Electron Flow 730 19.9 ATP Synthesis by Photophosphorylation 740 ylation in NADP* as ult olutely differ- If an idea presents itself to us, we must not reject it simply because it does not agree with the logical deductions of a reigning theory. -Claude Bemard, An Introduction to the The aspect of the present position find most remarkable and admirable, is is the altruism and generosity with which former opponents of the chemiosmotic hypothesis have not only come to acce but have actively promoted it to the status of a theory. -Peter Mitchell, Nobel Address, 1978 espects. (1)Both 690chapter Oxidative phosphorylation is the culmination of energy￾yielding metabolism in aerobic organisms. All oxi￾dative steps in the degradation of carbohydrates, fats, and amino acids converge at this final stage of cellular respiration, in which the energy of oxidation drives the synthesis of ATP. Photophosphorylation is the means by which photosynthetic organisms capture the energy of sunlight—the ultimate source of energy in the bio￾sphere—and harness it to make ATP. Together, oxida￾tive phosphorylation and photophosphorylation account for most of the ATP synthesized by most organisms most of the time. In eukaryotes, oxidative phosphorylation occurs in mitochondria, photophosphorylation in chloroplasts. Oxidative phosphorylation involves the reduction of O2 to H2O with electrons donated by NADH and FADH2; it occurs equally well in light or darkness. Photophosphor￾ylation involves the oxidation of H2O to O2, with NADP
as ultimate electron acceptor; it is absolutely dependent on the energy of light. Despite their differ￾ences, these two highly efficient energy-converting processes have fundamentally similar mechanisms. Our current understanding of ATP synthesis in mi￾tochondria and chloroplasts is based on the hypothesis, introduced by Peter Mitchell in 1961, that transmem￾brane differences in proton concentration are the reser￾voir for the energy extracted from biological oxidation reactions. This chemiosmotic theory has been ac￾cepted as one of the great unifying principles of twen￾tieth century biology. It provides insight into the processes of oxidative phosphorylation and photophos￾phorylation, and into such apparently disparate energy transductions as active transport across membranes and the motion of bacterial flagella. Oxidative phosphorylation and photophosphoryla￾tion are mechanistically similar in three respects. (1) Both 19 690 OXIDATIVE PHOSPHORYLATION AND PHOTOPHOSPHORYLATION If an idea presents itself to us, we must not reject it simply because it does not agree with the logical deductions of a reigning theory. —Claude Bernard, An Introduction to the Study of Experimental Medicine, 1813 The aspect of the present position of consensus that I find most remarkable and admirable, is the altruism and generosity with which former opponents of the chemiosmotic hypothesis have not only come to accept it, but have actively promoted it to the status of a theory. —Peter Mitchell, Nobel Address, 1978 OXIDATIVE PHOSPHORYLATION 19.1 Electron-Transfer Reactions in Mitochondria 691 19.2 ATP Synthesis 704 19.3 Regulation of Oxidative Phosphorylation 716 19.4 Mitochondrial Genes: Their Origin and the Effects of Mutations 719 19.5 The Role of Mitochondria in Apoptosis and Oxidative Stress 721 PHOTOSYNTHESIS: HARVESTING LIGHT ENERGY 19.6 General Features of Photophosphorylation 723 19.7 Light Absorption 725 19.8 The Central Photochemical Event: Light-Driven Electron Flow 730 19.9 ATP Synthesis by Photophosphorylation 740 8885d_c19_690-750 3/1/04 11:32 AM Page 690 mac76 mac76:385_reb: