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Chapter 7 Microbial Metabolism Metabolism is the sum of cellular chemical and physical activities. It consists of anabolism, synthetic reactions that convert small molecules into large molecules, and catabolism, in which large molecules are degraded and energy is produced. Metabolism is made possible by organic catalysts, or enzymes, that speed up reactions to rates compatible with biological processes. Enzymes are not consumed and can be reused. Each enzyme acts specifically upon its matching molecule or substrate. Enzymes are labile (unstable) and function only within narrow operating ranges of temperature, osmotic pressure, and pH, and they are especially vulnerable to denaturation. Enzymes are frequently the targets for physical and chemical agents used in control of microbes. Energy is the capacity of a system to perform work. It is consumed in endergonic reactions and is released in exergonic reactions. Extracting energy requires a series of electron carriers arrayed in a redox chain between electron donors and electron acceptors. Carbohydrates, such as glucose, are energy-rich because when catabolized they can yield a large number of electrons per molecule. Glycolysis is a pathway that degrades glucose to pyruvic acid without requiring oxygen. Pyruvic acid is processed in aerobic respiration via the Krebs cycle and its associated electron transport chain. Pyruvic acid undergoes further oxidation and decarboxylation in the Krebs cycle, which generates ATP, CO2, and large amounts of reduced carriers (NADH and FADH2).The respiratory chain then completes energy extraction and the final electron acceptor in aerobic respiration is oxygen. In anaerobic respiration, compounds such as sulfate, nitrate, or nitrite serve this function. Fermentation is anaerobic respiration in which both the electron donor and final electron acceptors are organic compounds. Production of alcohol, vinegar, and certain industrial solvents relies upon fermentation. Glycolysis and the Krebs cycle are central pathways that link catabolic and anabolic pathways, allowing cells to break down different classes of molecules in order to synthesize compounds required by the cell. Metabolism and the Role of Enzymes 1. Describe the relationship among metabolism, catabolism, and anabolism. 2. Fully define the structure and function of enzymes. 3. Differentiate between constitutive and regulated enzymes. 4. Diagram some different patterns of metabolism. 5. Describe how enzymes are controlled. The Pursuit and Utilization of Energy 6. Name the chemical in which energy is stored in cells. 7. Create a general diagram of a redox reaction. 8. Identify electron carriers used by cells. Catabolism 9. Name three basic catabolic pathways, and give an estimate of how much ATP each of them yields. 10. Write a summary statement describing glycolysis. 11. Describe the Krebs cycle. 12. Discuss the significance of the electron transport system. 13. Point out how anaerobic respiration differs from aerobic respiration. 14. Provide a summary of fermentation. 15. Describe how noncarbohydrate compounds are catabolized. Anabolism and the Crossing Pathways of Metabolism 16. Provide an overview of the anabolic stages of metabolism. 17. Define amphibolism. Key Terms and Phrases Anabolism Catabolism Metabolism Enzymes Catalysts Substrate Holoenzyme Apoenzyme Cofactors Active site Coenzymes Vitamins Constitutive enzymes Oxidized Reduced Labile Denaturation Competitive inhibition Catalytic site Substrate Enzyme repression Enzyme induction Endergonic Exergonic Denitritification Phosphorylate Lipases Final electron acceptor Proteases FAD ATP Glycolysis Krebs Cycle Aerobic respiration Ferment Anaerobic respiration Pyruvic acid Electron transport Fermentation Amphibolism Deanimation ATP Synthase Oxidative phosphorylation Cytochromes Amination Beta oxidation Non-competitive inhibiton