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  • 1. PowerPoint to accompanyFoundations in Microbiology Fifth Edition Talaro Chapter 8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 2. Microbial Metabolism: The Chemical Crossroads of Life Chapter 8
  • 3. Metabolism The sum total of all chemicalreactions & physical workings occurring in a cell
  • 4. 2 types of metabolism• Anabolism - biosynthesis – building complex molecules from simple ones – requires energy (ATP)• Catabolism - degradation – breaking down complex molecules into simple ones – generates energy (ATP) 4
  • 5. 5
  • 6. 6
  • 7. 7
  • 8. Enzyme structure• Simple enzymes – consist of protein alone• Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules – apoenzyme –protein portion – cofactors – nonprotein portion • metallic cofactors – iron, copper, magnesium • coenzymes -organic molecules - vitamins 8
  • 9. 9
  • 10. Enzyme-substrate interactions 10
  • 11. • Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase• Endoenzymes – retained intracellularly & function there 11
  • 12. 12
  • 13. • Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism• Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources 13
  • 14. 14
  • 15. • Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond• Hydrolysis reactions– catabolic reactions that break down substrates into small molecules, requires the input of water 15
  • 16. 16
  • 17. Transfer reactions by enzymes1. Oxidation-reduction reactions – transfer of electrons2. Aminotransferases – convert one type of amino acid to another by transferring an amino group3. Phosphotransferases – transfer phosphate groups, involved in energy transfer4. Methyltransferases – move methyl groups from one molecule to another5. Decarboxylases – remove carbon dioxide from organic acids 17
  • 18. Metabolic pathways 18
  • 19. Control of enzyme activity1. Competitive inhibition – substance that resembles normal substrate competes with substrate for active site2. Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme3. Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes4. Enzyme induction – enzymes are made only when suitable substrates are present 19
  • 20. Competitive inhibition 20
  • 21. Energy –capacity to do work or cause change• Endergonic reactions – consume energy• Exergonic reactions – release energy 21
  • 22. Redox reactions• always occur in pairs• There is an electron donor and electron acceptor which constitute a redox pair• The process salvages electrons & their energy.• released energy can be captured to phosphorylate ADP or another compound 22
  • 23. Electron carriers• resemble shuttles that are loaded and unloaded with electrons and hydrogen• most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain 23
  • 24. NAD reduction 24
  • 25. Electron carriers 25
  • 26. ATP• 3 part molecule consisting of – adenine – a nitrogenous base – ribose – a 5-carbon sugar – 3 phosphate groups• Removal of the terminal phosphate releases energy 26
  • 27. ATP 27
  • 28. Phosphorylation of glucose by ATP 28
  • 29. Formation of ATP1. substrate-level phosphorylation2. oxidative phosphorylation3. photophosphorylation 29
  • 30. substrate-level phosphorylation 30
  • 31. Catabolism of glucose1. Glycolysis2. Tricarboxylic acid cycle, Kreb’s cycle3. Respiratory chain, electron transport 31
  • 32. Metabolic strategies Pathways Final e- involved acceptor ATP yieldAerobic Glycolysis, O2 38respiration TCA, ETAnaerobic Glycolysis, NO3-, So4-2, variablerespiration TCA, ET CO3-3Fermentation Glycolysis Organic 2 molecules 32
  • 33. Overview of aerobic respiration 33
  • 34. Overview of aerobic respiration• Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C)• TCA – processes pyruvic acid and generates 3 CO2 molecules• Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation 34
  • 35. Glycolysis 35
  • 36. TCA cycle 36
  • 37. Electron transport system 37
  • 38. Chemiosmosis 38
  • 39. Fermentation• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen• Uses organic compounds as terminal electron acceptors• Yields a small amount of ATP• Production of ethyl alcohol by yeasts acting on glucose• Formation of acid, gas & other products by the action of various bacteria on pyruvic acid 39
  • 40. Fermentation 40
  • 41. Products of fermentation 41
  • 42. • Many pathways of metabolism are bi-directional or amphibolic• Metabolites can serve as building blocks or sources of energy – Pyruvic acid can be converted into amino acids through amination – Amino acids can be converted into energy sources through deamination – Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates and fats 42
  • 43. 43
  • 44. 44