Microbial Metabolism


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Microbial Metabolism

  1. 1. Foundations in Microbiology Chapter 8 PowerPoint to accompany Fifth Edition Talaro Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Microbial Metabolism: The Chemical Crossroads of Life Chapter 8
  3. 3. Metabolism The sum total of all chemical reactions & physical workings occurring in a cell
  4. 4. 2 types of metabolism <ul><li>Anabolism - biosynthesis </li></ul><ul><ul><li>building complex molecules from simple ones </li></ul></ul><ul><ul><li>requires energy (ATP) </li></ul></ul><ul><li>Catabolism - degradation </li></ul><ul><ul><li>breaking down complex molecules into simple ones </li></ul></ul><ul><ul><li>generates energy (ATP) </li></ul></ul>
  5. 8. Enzyme structure <ul><li>Simple enzymes – consist of protein alone </li></ul><ul><li>Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules </li></ul><ul><ul><li>apoenzyme –protein portion </li></ul></ul><ul><ul><li>cofactors – nonprotein portion </li></ul></ul><ul><ul><ul><li>metallic cofactors – iron, copper, magnesium </li></ul></ul></ul><ul><ul><ul><li>coenzymes -organic molecules - vitamins </li></ul></ul></ul>
  6. 10. Enzyme-substrate interactions
  7. 11. <ul><li>Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase </li></ul><ul><li>Endoenzymes – retained intracellularly & function there </li></ul>
  8. 13. <ul><li>Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism </li></ul><ul><li>Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources </li></ul>
  9. 15. <ul><li>Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond </li></ul><ul><li>Hydrolysis reactions – catabolic reactions that break down substrates into small molecules, requires the input of water </li></ul>
  10. 17. Transfer reactions by enzymes <ul><li>Oxidation-reduction reactions – transfer of electrons </li></ul><ul><li>Aminotransferases – convert one type of amino acid to another by transferring an amino group </li></ul><ul><li>Phosphotransferases – transfer phosphate groups, involved in energy transfer </li></ul><ul><li>Methyltransferases – move methyl groups from one molecule to another </li></ul><ul><li>Decarboxylases – remove carbon dioxide from organic acids </li></ul>
  11. 18. Metabolic pathways
  12. 19. Control of enzyme activity <ul><li>Competitive inhibition – substance that resembles normal substrate competes with substrate for active site </li></ul><ul><li>Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme </li></ul><ul><li>Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes </li></ul><ul><li>Enzyme induction – enzymes are made only when suitable substrates are present </li></ul>
  13. 20. Competitive inhibition
  14. 21. Energy –capacity to do work or cause change <ul><li>Endergonic reactions – consume energy </li></ul><ul><li>Exergonic reactions – release energy </li></ul>
  15. 22. Redox reactions <ul><li>always occur in pairs </li></ul><ul><li>There is an electron donor and electron acceptor which constitute a redox pair </li></ul><ul><li>The process salvages electrons & their energy. </li></ul><ul><li>released energy can be captured to phosphorylate ADP or another compound </li></ul>
  16. 23. Electron carriers <ul><li>resemble shuttles that are loaded and unloaded with electrons and hydrogen </li></ul><ul><li>most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain </li></ul>
  17. 24. NAD reduction
  18. 25. Electron carriers
  19. 26. ATP <ul><li>3 part molecule consisting of </li></ul><ul><ul><li>adenine – a nitrogenous base </li></ul></ul><ul><ul><li>ribose – a 5-carbon sugar </li></ul></ul><ul><ul><li>3 phosphate groups </li></ul></ul><ul><li>Removal of the terminal phosphate releases energy </li></ul>
  20. 27. ATP
  21. 28. Phosphorylation of glucose by ATP
  22. 29. Formation of ATP <ul><li>substrate-level phosphorylation </li></ul><ul><li>oxidative phosphorylation </li></ul><ul><li>photophosphorylation </li></ul>
  23. 30. substrate-level phosphorylation
  24. 31. Catabolism of glucose <ul><li>Glycolysis </li></ul><ul><li>Tricarboxylic acid cycle, Kreb’s cycle </li></ul><ul><li>Respiratory chain, electron transport </li></ul>
  25. 32. Metabolic strategies 2 Organic molecules Glycolysis Fermentation variable NO 3 - , So 4 -2 , CO 3 -3 Glycolysis, TCA, ET Anaerobic respiration 38 O 2 Glycolysis, TCA, ET Aerobic respiration ATP yield Final e- acceptor Pathways involved
  26. 33. Overview of aerobic respiration
  27. 34. Overview of aerobic respiration <ul><li>Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C) </li></ul><ul><li>TCA – processes pyruvic acid and generates 3 CO 2 molecules </li></ul><ul><li>Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation </li></ul>
  28. 35. Glycolysis
  29. 36. TCA cycle
  30. 37. Electron transport system
  31. 38. Chemiosmosis
  32. 39. Fermentation <ul><li>Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen </li></ul><ul><li>Uses organic compounds as terminal electron acceptors </li></ul><ul><li>Yields a small amount of ATP </li></ul><ul><li>Production of ethyl alcohol by yeasts acting on glucose </li></ul><ul><li>Formation of acid, gas & other products by the action of various bacteria on pyruvic acid </li></ul>
  33. 40. Fermentation
  34. 41. Products of fermentation
  35. 42. <ul><li>Many pathways of metabolism are bi-directional or amphibolic </li></ul><ul><li>Metabolites can serve as building blocks or sources of energy </li></ul><ul><ul><li>Pyruvic acid can be converted into amino acids through amination </li></ul></ul><ul><ul><li>Amino acids can be converted into energy sources through deamination </li></ul></ul><ul><ul><li>Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates and fats </li></ul></ul>