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  1. 1. Chapter 8 Microbial Metabolism: The Chemical Crossroads of Life Chapter Summary This chapter covers the metabolism of microorganisms. It examines the nature of enzymes, function of enzymes, the ebbing flow of energy through the cell, and glucose catabolic pathways. The student would benefit the greatest if they already possess a knowledge of human metabolism, which will be broadened in respect to microbes, in this chapter. Chapter Outline I. The Metabolism of Microbes A. Metabolism 1.Anabolism 2. Catabolism B. Role of ATP and metabolites C. Enzymes: Catalyzing the Chemical Reactions of Life: Enzymes as Catalysts 1. How Do Enzymes Work? a. Energy of activation b. Substrates 2. Enzyme Structure a. Simple enzymes b. Conjugated enzymes c. Holoenzyme i. Apoenzyme ii. Cofactors 3. Apoenzymes: Specificity and the Active Site (catalytic sites) 4. Enzyme-Substrate Interactions a. Induced fit model of action b. Enzyme-substrate complex 5. Cofactors: Supporting the Work of Enzymes a. Metallic cofactors b. Coenzymes and vitamins 6. Classification of Enzyme Functions a. Location and Regularity of Enzyme Action i. Exoenzymes ii. Endoenzymes iii. Constitutive enzymes iv. Induced (inducible) enzymes b. Synthesis and Hydrolysis Reactions i. Condensation reactions ii. Hydrolysis reaction c. Transfer Reactions by Enzymes i. Oxidation and reduction: oxidoreductases ii. Aminotransferases iii. Phosphotransferases iv. Methyltransferases v. Decarboxylases 7. The Role of Microbial Enzymes in Disease a. Streptococcus pyogenes b. Pseudomonas aeruginosa 26
  2. 2. c. Clostridium perfringens 8. The Sensitivity of Enzymes to Their Environments a. Labile b. Denaturation 9. Regulation of Enzymatic Activity and Metabolic Pathways a. Metabolic Pathways b. Direct Controls on the Actions of Enzymes i. Competitive Inhibition ii. Feedback Control: positive or negative c. Controls on Enzyme Synthesis i. Enzyme repression ii. Enzyme induction: Escherichia coli II. The Pursuit and Utilization of Energy: definition of energy A. Cell energetics 1. Exergonic 2. Endergonic B. A Closer Look at Biological Oxidation and Reduction 1. Redox reactions 2. Phosphorylation and ATP synthesis 3. Electron transfer 4. Dehydrogenation 5. Electron Carriers: Molecular Shuttles a. NADH b. Final electron acceptor: oxygen C. Adenosine Triphosphate: Metabolic Money 1. The Molecular Structure of ATP: phosphate, sugar and a base 2. The Metabolic Role of ATP a. Substrate-level phosphorylation b. Oxidative phosphorylation c. Photophosphorylation III. Pathways of Bioenergetics A. Catabolism: An Overview of Nutrient Breakdown and Energy Release 1. Glycolysis 2. Tricarboxylic Acid Cycle (Kreb's cycle) 3. Respiratory Chain: Electron Transport and Oxidative Phosphorylation B. Energy Strategies in Microorganisms 1. Aerobic Respiration a. Glycolysis: The Starting Lineup i. An anaerobic step ii. Pyruvic acid synthesis iii. Steps in the Glycolytic Pathway b. Pyruvic Acid: A Central Metabolite c. The Tricarboxylic Acid Cycle: A Carbon and Energy Wheel i. The processing of pyruvic acid ii. Acetyl coenzyme A role iii. Role of NADH iv. Steps in the TCA cycle d. The Respiratory Chain: Electron Transport And Oxidative Phosphorylation i. Role of ATP synthase ii. Oxidative phosphorylation iii. Potential Yield of ATPs from Oxidative Phosphorylation e. Summary of Aerobic Respiration 27
  3. 3. i. The Terminal Step: formation of water ii. Neisseria,, Pseudomonas, Bacillus iii. Klebsiella,, Enterobacter iv. Streptococcus v. Superoxide dismutase and catalase f. Alternate Catabolic Pathways C. Anaerobic Respiration 1. E. coli 2. Pseudomonas and Bacillus 3. Denitrification D. The Importance of Fermentation E. Products of Fermentation 1. Alcoholic fermentation 2. Acidic fermentation a. Streptococcus and Lactobacillus: homolactic fermentation b. Leuconostoc: heterolactic fermentation 3. Mixed acid fermentation: Propionibacterium IV. Biosynthesis and the Crossing Pathways of Metabolism A. The Frugality of the Cell: Waste Not, Want Not 1. Amphibolic Sources of Cellular Building Blocks a. Gluconeogenesis b. Beta-oxidation c. Amination 2. Formation of Macromolecules 3. Amino Acids, and Protein and Nucleic Acid Synthesis 4. Carbohydrate Biosynthesis 28
  4. 4. Key Terms and Phrases anabolism induced enzymes final electron acceptor catabolism oxidized NAD metabolites reduced FAD enzymes labile ATP catalysts denaturation glycolysis energy of activation competitive inhibition TCA substrate negative feedback Kreb's Cycle holoenzyme allosteric aerobic respiration apoenzyme regulatory ferment cofactors enzyme repression anaerobic respiration coenzymes enzyme induction pyruvic acid active site energy ETS metallic cofactors potential energy phosphogluconate pathway coenzymes kinetic energy fermentation hydrolysis endergonic amphibolism allosteric exergonic gluconeogenesis exoenzyme redox reactions beta oxidation endoenzyme phosphorylate amination constitutive enzymes dehydrogenation Topics for Discussion A review of cellular metabolism, both anabolic and catabolic will help the student with the material in this chapter. The lecture is fairly tedious, but very necessary if the students are to understand how the antibiotics and other chemicals work against the microorganism. Students should compare the effectiveness of aerobic versus anaerobic reactions that produce energy. Discuss the role of vitamins, minerals and nucleotides in energy production. Create a list of useful products of fermentation. 29