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7.8Summary

  • Metabolism fulfills the two roles of acting as a prime mover to drive cellular activity through the nonequilibrium flow of energy and interconverting a range of biological substances.
  • Energy obtained from metabolites is stored as ATP, which is hydrolyzed to ADP during material syntheses that require energy. ATP can therefore be thought of as the “currency” of biological energy.
  • Metabolic pathways in cells are formed by many enzymes, which are biocatalysts and have specificity for substrate binding and reactions they catalyze. Enzymatic reactions can be expressed by the Michaelis-Menten equation, with which substrate binding strength and inhibitors can be analyzed.
  • Basic metabolic pathways in a cell connect the following three levels: 1) complex molecules such as proteins, polysaccharides, lipids, etc., 2) their constituent units (namely, amino acids, monosaccharides, fatty acids, etc.), and 3) the intermediate metabolites that metabolically connect them.
  • While metabolic reactions differ, they share a number of typical patterns. It is necessary to understand the mechanisms behind the formation and degradation of phosphoester bonds, the formation and degradation of C-C bonds and dehydrogenation, among other reactions.
  • Glycolysis and the citric acid cycle - examples of metabolic pathways - are important as systems for energy production.
  • Many enzymes are subject to expression regulation at the gene level and to allosteric regulation by effectors and modification such as phosphorylation. By these processes, the balance of cellular metabolisms is maintained.
  • In allosteric regulation, through cooperative changes in the higher-order structure of enzymatic molecules, enzymatic activity is turned on and off in accordance with slight changes in the concentration of effectors. In many cases, activity regulation takes place as a result of feedback from metabolites. In regulation by phosphorylation, multi-stage cascades amplify small inputs.

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