19 Oxidative Phosphorylation

19 Oxidative Phosphorylation - B iochemis ry E duca ion...

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Unformatted text preview: B iochemis ry E duca ion Department of iochemistry & Molecular iology University of New Mexico BIOC 423 Int oducto y Biochemist y Oxidative Phosphorylation OBJECTIVES Understand the physical organization of components of the electron transport chain. Know the structures of the functional parts of the coenzymes involved in electron transport (FAD, NAD+, ubiquinone, cytochromes). Be able to diagram the flow of electrons through the transport system indicating the sites of entry of NADH and FADH 2 . Know how the energy derived from electron transport is used to synthesize ATP. Know how ATP leaves the mitochondrion. Know how the electrons from cytosolic NADH enter the mitochondrion. Understand how the rate of oxidative phosphorylation is controlled. OUTLINE Transport of Electron Donors into the Mitochondria Malate dehydrogenase shuttle Glycerol 3-phosphate dehydrogenase shuttle ATP transport Electron Transport Chain - Oxidation ATP Synthesis - Phosphorylation Substrate level phosphorylation P/O ratios Chemiosmotic theory F0/F1 ATP Synthase Thermogenesis and uncoupling LECTURE This is the last lecture in the energy metabolism section of the course. In reality we have seen very little ATP generated in the pathways which we have considered. The ATP (or GTP) equivalents that have been generated by substrate level phosphorylation are limited to three different reactions; phosphoglycerate kinase, pyruvate kinase, and succinate thiokinase. However, a common factor in all of the pathways that we have been studying is the production of NADH or FADH 2 . Remember that there is energy in these reduced molecules and to complete energy metabolism we need to convert this reducing power to the metabolic energy of ATP. That pathway that does that is oxidative phosphorylation in which the reducing power of NADH and FADH 2 is transferred to the final electron acceptor, usually molecular oxygen. The final electron acceptor, however, varies for different organisms. For aerobes the acceptor is oxygen. Anaerobes have the capability of reducing a variety of different molecules to accept the electron. Transport of Electron Donors into the Mitochondria The mitochondria has been called the furnace of the cell because that is the organelle which ultimately combines oxygen with the reduced component of the fuel molecules. This happens in the matrix of the mitochondria, on the inner surface of the inner membrane. With the mitochondria we again have our common problem, which we have seen many times, that of moving materials to the proper location. For the CAC and beta oxidation, which takes place in the matrix, we have no problem because the NADH and FADH2 are generated in the proper location. However for glycolysis NADH is generated in the cytoplasm. Whereas ATP and ADP +Pi have a facilitated diffusion transport system available, there is no similar transport system for NAD + and NADH. The solution to this problem is to shuttle the NADH across the membrane in the form of other chemicals. Two of these shuttle systems are outlined below. In these transport systems the cytoplasmic NADH is used to reduce a metabolite,...
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19 Oxidative Phosphorylation - B iochemis ry E duca ion...

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