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MCB100 Introductory Microbiology February 27, 2019 Chapter 5 - Microbial Metabolism

MCB100 Introductory Microbiology February 27, 2019 Chapter 5 - Microbial Metabolism. Glycolysis Summarized 10 reactions, makes 2 ATPs per glucose (profit) 1 glucose molecule  2 molecules of pyruvate C 6 H 12 O 6  2C 3 H 4 O 3

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MCB100 Introductory Microbiology February 27, 2019 Chapter 5 - Microbial Metabolism

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  1. MCB100 Introductory Microbiology February 27, 2019 Chapter 5 - Microbial Metabolism

  2. Glycolysis Summarized 10 reactions, makes 2 ATPs per glucose (profit) 1 glucose molecule  2 molecules of pyruvate C6H12O6 2C3H4O3 But that’s not the complete story. The above is not a balanced chemical reaction. There are 12 hydrogens on the left side of the equation and 8 on the right. Where did those 4 hydrogen atoms go?

  3. Glycolysis Summarized 10 reactions, makes 2 ATPs per glucose (profit) 1 glucose molecule  2 molecules of pyruvate C6H12O6  2 C3H4O3 2 NAD+ 2 (NADH + H+) 2 ADP + 2 H3PO4 2 ATP + 2 H2O

  4. 2Pyruvates  6CO2 (PDH & TCA)

  5. The Pyruvate Dehydrogenase Reaction Summarized 2 molecules + 2 molecules  2 acetyl-CoA + 2 CO2of pyruvate of Coenzyme A 2C3H4O3 + 2 CoASH  2C2H3O-S-CoA Again, the above isn’t a balanced chemical equation. There are 10 hydrogens on the left and 6 on the right. Where did those 4 hydrogen atoms go? 2NAD+ + 4H  2(NADH + H+)

  6. Intermediates of Glycolysis and the Krebs Cycle Which one of the compounds given below is a 4-carbon Krebs cycle intermediate that can be used as a starting material for citric acid synthesis?A. fructose 1,6-bisphosphate B. glyceraldehyde-3-phosphate C. pyruvate D. oxaloacetic acid E. alpha-keto-glutarate

  7. Intermediates of Glycolysis and the Krebs Cycle Which one of the compounds given below is a 4-carbon Krebs cycle intermediate that can be used as a starting material for citric acid synthesis?A. fructose 1,6-bisphosphate B. glyceraldehyde-3-phosphate C. pyruvate D. oxaloacetic acid E. alpha-keto-glutarate

  8. The Krebs Cycle Summarized2 ATPs are generated by substrate-level phosphorylation. 2 C2H3O-S-CoA + 2 OAA  2 OAA + 2 CoASH + 4 CO2 I see 2 oxaloacetic acid molecules (OAA) on both the left and right sides of the formula so they cancel each other out. And I see 4 carbons in the 2 acetate groups on the left and 4 carbons in the CO2 on the right. So the carbon is balanced. But I see 2 oxygens on the left (in the 2 acetate groups) and 8 oxygens in the CO2 on the right. Where did the 6 extra oxygens come from?

  9. The Krebs Cycle SummarizedWhere did the 6 extra oxygens come from? Not from O2. The Krebs cycle can happen in the absence of air. Those oxygen atoms come from water molecules. So let’s add them in. 2 C2H3O-S-CoA +6H2O  2 CoASH + 4 CO2 Okay, now it’s balanced for oxygen, but on the left side I see 6 hydrogens in the 2 acetate groups and 12 hydrogens in the water while on the right I just see 2 hydrogens in the CoASH. Where did the 16 hydrogens go? 6NAD+ + 12H  6(NADH + H+) and 2FAD + 4H  2 FADH2

  10. The Kreb's cycle: 8 reactions that result in the oxidation of pyruvate to CO2. See pages 140-1431 of your textbook. When two molecules of pyruvate are oxidized to six molecules of carbon dioxide: 8 molecules of NAD+ are reduced to NADH + H+ 2 molecules of FAD are reduced to FADH2 2 ATPs made by substrate level phosphorylation At the end of glycolysis and the Kreb’s cycle the glucose has been oxidized to 6 molecules of CO2 and 10 molecules of NAD+ and 2 molecules of FAD have been reduced to NADH + H+ and FADH2.

  11. Glycolysis and Krebs Cycle Redox Reactions Summarized C6H12O6 + 6H2O + 10NAD+ + 2FAD  6CO2 + 10(NADH + H+) + 2FADH2

  12. Electron Transport Chain Oxidative phosphorylationis a series of redox reactions involving membrane bound enzymes and electron carriers that results in the reoxidation of NADH + H+ back to NAD+, the reduction of O2 to H2O and the production of about 34 ATPs per glucose. See pages 138 – 141 of the textbook. Oxidative phosphorylation yields a Proton Motive Force (PMF) that is sufficient to produce about 3 ATPs per NADH oxidized and 2 ATPs per FADH2 oxidized.

  13. The Electron Transport Chain (ETC) is a series of enzymes and electron carriers embedded in a membrane. The ETC is located in the mitochondrial membrane in eukaryotic cells and in the cytoplasmic membrane in bacteria. 1) NADH + H+ is oxidized to NAD+ 2) Electrons are passed from carrier to carrier, protons are pumped across membrane. 3) Oxygen is reduced to water, in aerobic respiration oxygen is the terminal electron acceptor. Protons flow through ATP synthase and generate ATP from ADP + Pi. outside the cell or mitochondria membrane inside cell or mitochondria

  14. The overall reaction of the electron transport chain in aerobic respiration 2NADH + 2H+ + O2  2NAD+ + 2H2O An energetically similar redox reaction 2H2 + O2  2H2O

  15. Electron Transport Chain

  16. Redox Reactions of the Electron Transport Chain Summarized 10(NADH + H+) + 2FADH2 + 6O2 12H2O + 10NAD+ + 2FAD Aerobic Respiration of Glucose C6H12O6 + 6O26CO2 + 6H2O

  17. Utilization of the • Proton Motive Force • A proton gradient across a membrane can be used to drive several processes, including: • - ATP synthesis, • - active uptake of nutrients, • - ion pumps, and • flagella rotation • For each NADH + H+ oxidized to NAD+ • by the electron transport chain, a cellcan make 3 ATPs. • For each FADH2 oxidized to FAD • by the electron transport chain, a cellcan make 2 ATPs. diagram from: Ken Todar University of Wisconsin – Madison

  18. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide and Water Steps 1) Glycolysis 2) Krebs Cycle 3) Electron Transport Chain and Oxidative Phosphorylation Aerobic respiration yields about 38 ATPs per glucose molecule consumed. GlycolysisKrebs CycleETC and OP makes: 4 ATPs makes 2 GTPs 2FADH2 FAD uses: - 2 ATPs 10NADH  NAD+ profit = 2 ATPs 8NAD+ 8NADH 2FAD  2FADH2 makes PMF that 2NAD+ 2NADH can make 34 ATPs

  19. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide In the oxidation of glucose to carbon dioxide what reactions produce carbon dioxide? Assume aerobic respiration. Choose the best answer. A. Glycolysis and the Electron Transport Chain B. The Pyruvate Dehydrogenase reaction and Krebs Cycle C. Only the Krebs Cycle D. Only the Electron Transport Chain E. Only Glycolysis

  20. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide In the oxidation of glucose to carbon dioxide what reactions produce carbon dioxide? Assume aerobic respiration. Choose the best answer. A. Glycolysis and the Electron Transport Chain B. The Pyruvate Dehydrogenase reaction and Krebs Cycle C. Only the Krebs Cycle D. Only the Electron Transport Chain E. Only Glycolysis

  21. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide In the oxidation of glucose to carbon dioxide what reactions require non-combined oxygen (O2)? Assume aerobic respiration. Choose the best answer. A. Glycolysis and the Electron Transport Chain B. The Pyruvate Dehydrogenase reaction and Krebs Cycle C. Only the Krebs Cycle D. Only the Electron Transport Chain E. Only Glycolysis

  22. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide In the oxidation of glucose to carbon dioxide what reactions require non-combined oxygen (O2)? Assume aerobic respiration. Choose the best answer. A. Glycolysis and the Electron Transport Chain B. The Pyruvate Dehydrogenase reaction and Krebs Cycle C. Only the Krebs Cycle D. Only the Electron Transport Chain E. Only Glycolysis

  23. Aerobic Respiration Oxidation of Glucose to Carbon Dioxide and Water Steps 1) Glycolysis 2) Krebs Cycle 3) Electron Transport Chain and Oxidative Phosphorylation Aerobic respiration yields about 38 ATPs per glucose molecule consumed. GlycolysisKrebs CycleETC and OP makes: 4 ATPs makes 2 GTPs 2FADH2 FAD uses: - 2 ATPs 10NADH  NAD+ profit = 2 ATPs 8NAD+ 8NADH 2FAD  2FADH2 makes PMF that 2NAD+ 2NADH can make 34 ATPs

  24. Alternatives to Aerobic Respiration (Seen in Chemoheterotrophic Microorganisms) Anaerobic Respiration food source = organic matter (sugars etc.) final oxidizing agent = an oxidized mineral Major means of ATP production: ETC & PMF

  25. Anaerobic respiration is similar to aerobic respiration in that NADH + H+ is oxidized back to NAD+ using a membrane bound electron transfer chain but the terminal electron acceptor is not oxygen but rather some oxidized mineral. If the proper mineral is present, the bacteria can use respiration to produce energy in the absence of air. Electron Transport Chain - ANAEROBIC RESPIRATION (outside of cell) H+ H+ H+ H+ H+H+H+ H+ H+ H+ H+ . membrane  ATP ___ETC_  synthase . NADH + H+NO3-ADP + Pi H+ ATP NAD+NO2- + H2O (inside cell)

  26. AEROBIC vs. ANAEROBIC RESPIRATION Oxidizing_Agent Reduced_Waste_Product Aerobic Elemental Oxygen O2 H2O Anaerobic Nitrate NO3-Nitrite NO2- + H2O Nitrite NO2- Nitrogen or Nitrous oxide N2 or N2O + H2O Sulfate SO42- Sulfite SO32- + H2O Sulfite SO32- Hydrogen Sulfide or Sulfur H2S or So + H2O Carbonate CO32- Methane CH4 + H2O (in both cases the reducing reagent = NADH)

  27. Anaerobic Chemoheterotrophic Metabolism Anaerobic Respiration - ATP generation via PMF - terminal electron acceptor is an oxidized mineral The ATP yield from Anaerobic Respiration varies a lot, but may be able to produce up to 36 ATPs per glucose. (for bacteria lucky enough to have glucose for food) Examples of bacteria that can use anaerobic respiration: Bacteria in the Enterobacteriaceae family, including: Esherichia coli, Proteus vulgaris and Salmonella species can reduce nitrate (NO3-) to nitrite (NO2-). Some soil bacteria, such as: Pseudomonas and Bacillus species can reduce nitrate (NO3-) to nitrite (NO2-) and then to nitrogen (N2) or nitrous oxide (N2O). Bacteria in the Desulfovibrionales family reduce Sulfate (SO42-) and Sulfite (SO32-) to H2S.

  28. Denitrification is a form of anaerobic respiration that uses nitrate and nitrite as the terminal electron acceptor. Nitrate and nitrite get reduced to nitrogen or nitrous oxide. Nitrate is mobile in ground water and is the form of nitrogen that green plants need for growth. Nitrogen and nitrous oxide are gases that can’t be used by plants. This form of metabolism is called denitrification because it converts a form of nitrogen which can be used by plants to a form that plants can’t use. Denitrification - anaerobic - organic matter is oxidized - nitrate is converted to nitrogen

  29. Glucose Catabolism by Aerobic vs. Anaerobic Respiration Glycolysis, Pyruvate Dehydrogenase Reaction and Krebs Cycle C6H12O6+6H2O+10NAD++2FAD  6CO2+10(NADH + H+)+2FADH2 In aerobic respiration an ETC is used to make a PMF. 2NADH + 2H+ + O2  2NAD+ + 2H2O In anaerobic respiration an ETC is used to make a PMF. NADH + H+ + NO3- NAD+ + H2O + NO2-

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