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Microbial metabolism4578
- 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. Microbial Metabolism: The Chemical Crossroads of Life Chapter 8
- 3. Metabolism The sum total of all chemical reactions & physical workings occurring in a cell
- 4. 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)
- 5. 5
- 6. 6
- 7. 7
- 8. 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
- 9. 9
- 11. 11 • Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase • Endoenzymes – retained intracellularly & function there
- 12. 12
- 13. 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
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- 15. 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
- 16. 16
- 17. 17 Transfer reactions by enzymes 1. Oxidation-reduction reactions – transfer of electrons 2. Aminotransferases – convert one type of amino acid to another by transferring an amino group 3. Phosphotransferases – transfer phosphate groups, involved in energy transfer 4. Methyltransferases – move methyl groups from one molecule to another 5. Decarboxylases – remove carbon dioxide from organic acids
- 19. 19 Control of enzyme activity 1. Competitive inhibition – substance that resembles normal substrate competes with substrate for active site 2. Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme 3. Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes 4. Enzyme induction – enzymes are made only when suitable substrates are present
- 21. 21 Energy –capacity to do work or cause change • Endergonic reactions – consume energy • Exergonic reactions – release energy
- 22. 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
- 23. 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
- 24. 24 NAD reduction
- 26. 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
- 27. 27 ATP
- 28. 28 Phosphorylation of glucose by ATP
- 29. 29 Formation of ATP 1. substrate-level phosphorylation 2. oxidative phosphorylation 3. photophosphorylation
- 31. 31 Catabolism of glucose 1. Glycolysis 2. Tricarboxylic acid cycle, Kreb’s cycle 3. Respiratory chain, electron transport
- 32. 32 Metabolic strategies Pathways involved Final e- acceptor ATP yield Aerobic respiration Glycolysis, TCA, ET O2 38 Anaerobic respiration Glycolysis, TCA, ET NO3 - , So4 -2 , CO3 -3 variable Fermentation Glycolysis Organic molecules 2
- 33. 33 Overview of aerobic respiration
- 34. 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
- 35. 35 Glycolysis
- 36. 36 TCA cycle
- 38. 38 Chemiosmosis
- 39. 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
- 40. 40 Fermentation
- 42. 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
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