Cells are systems in a dynamic steady state, maintained by a constant flux of nutrients that serve as energy sources or as raw material for the maintenance of cellular structures. Catabolism and anabolism are ongoing, concomitant processes. What principles underlie the integration of catabolism and energy production with anabolism and energy consumption? How is metabolism integrated in complex organisms with multiple organ systems? | Chapter 28 Metabolic Integration and Unidirectionality of Pathways to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline A Systems Analysis of Metabolism Metabolic Stoichiometry Unidirectionality Metabolism in a Multicellular Organism Systems Analysis of Metabolism Catabolic and anabolic pathways, occurring simultaneously, must act as a regulated, orderly, responsive whole See Figure - catabolism, anabolism and macromolecular synthesis Just a few intermediates connect major systems - sugar-Ps, alpha-keto acids, CoA derivs, and PEP ATP & NADPH couple catabolism & anabolism Phototrophs also have photosynthesis and CO2 fixation systems Metabolic Stoichiometry Three types of stoichiometry in biological systems Reaction stoichiometry - the number of each kind of atom in a reaction Obligate coupling stoichiometry - the required coupling of electron carriers Evolved coupling stoichiometry - the number of ATP molecules that pathways have evolved to consume or produce - a number that is a compromise, as we shall see The Significance of 38 ATPs The "ATP stoichiometry" has a large effect on the Keq of a reaction Consider the Keq for glucose oxidation (page 932) If 38 ATP are produced, cellular G is -967 kJ/mol and Keq = 10170, a very large number! If G = 0, 58 ATP could be made, but the reaction would come to equilibrium with only half as much glucose oxidized as we could have had So the number of 38 is a compromise! Significance of large Keq The more ATP obtained, the lower the equilibrium constant, and the higher the level of glucose required If [glucose] is below this value, it won't be effectively utilized Large Keq means that this threshold level of glucose will be be very low Large Keq also means that the . | Chapter 28 Metabolic Integration and Unidirectionality of Pathways to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline A Systems Analysis of Metabolism Metabolic Stoichiometry Unidirectionality Metabolism in a Multicellular Organism Systems Analysis of Metabolism Catabolic and anabolic pathways, occurring simultaneously, must act as a regulated, orderly, responsive whole See Figure - catabolism, anabolism and macromolecular synthesis Just a few intermediates connect major systems - sugar-Ps, alpha-keto acids, CoA derivs, and PEP ATP & NADPH couple catabolism & anabolism Phototrophs also have photosynthesis and CO2 fixation systems Metabolic Stoichiometry Three types of stoichiometry in biological systems Reaction stoichiometry
