cellular respiration and fermentation

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  • For the Discovery Video Space Plants, go to Animation and Video Files.
  • Figure 9.1 How do these leaves power the work of life for this chimpanzee?
  • Figure 9.2 Energy flow and chemical recycling in ecosystems.
  • Figure 9.UN01 In-text figure, p. 164
  • Figure 9.UN02 In-text figure, p. 164
  • Figure 9.3 Methane combustion as an energy-yielding redox reaction.
  • Figure 9.UN03 In-text figure, p. 165
  • Figure 9.4 NAD  as an electron shuttle.
  • Figure 9.UN04 In-text figure, p. 166
  • Figure 9.5 An introduction to electron transport chains.
  • Figure 9.UN05 In-text figure, p. 167
  • Figure 9.6 An overview of cellular respiration.
  • Figure 9.6 An overview of cellular respiration.
  • Figure 9.6 An overview of cellular respiration.
  • Figure 9.7 Substrate-level phosphorylation.
  • Figure 9.8 The energy input and output of glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis. Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.9 A closer look at glycolysis.
  • Figure 9.10 Oxidation of pyruvate to acetyl CoA, the step before the citric acid cycle.
  • Figure 9.11 An overview of pyruvate oxidation and the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • Figure 9.12 A closer look at the citric acid cycle.
  • For the Cell Biology Video ATP Synthase 3D Structure — Side View, go to Animation and Video Files. For the Cell Biology Video ATP Synthase 3D Structure — Top View, go to Animation and Video Files.
  • Figure 9.13 Free-energy change during electron transport.
  • Figure 9.14 ATP synthase, a molecular mill.
  • Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis.
  • Figure 9.16 ATP yield per molecule of glucose at each stage of cellular respiration.
  • Figure 9.17 Fermentation.
  • Figure 9.17 Fermentation.
  • Figure 9.17 Fermentation.
  • cellular respiration and fermentation

    1. 1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. JacksonChapter 9Cellular Respiration andFermentation Lectures by Erin Barley Kathleen Fitzpatrick© 2011 Pearson Education, Inc.
    2. 2. Overview: Life Is Work • Living cells require energy from outside sources • Some animals, such as the chimpanzee, obtain energy by eating plants, and some animals feed on other organisms that eat plants© 2011 Pearson Education, Inc.
    3. 3. Figure 9.1
    4. 4. • Energy flows into an ecosystem as sunlight and leaves as heat • Photosynthesis generates O2 and organic molecules, which are used in cellular respiration • Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work© 2011 Pearson Education, Inc.
    5. 5. Figure 9.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O Organic + O2 molecules Cellular respiration in mitochondria ATP powers ATP most cellular work Heat energy
    6. 6. Concept 9.1: Catabolic pathways yieldenergy by oxidizing organic fuels • Several processes are central to cellular respiration and related pathways© 2011 Pearson Education, Inc.
    7. 7. Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic • Fermentation is a partial degradation of sugars that occurs without O2 • Aerobic respiration consumes organic molecules and O2 and yields ATP • Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2© 2011 Pearson Education, Inc.
    8. 8. • Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)© 2011 Pearson Education, Inc.
    9. 9. Redox Reactions: Oxidation and Reduction • The transfer of electrons during chemical reactions releases energy stored in organic molecules • This released energy is ultimately used to synthesize ATP© 2011 Pearson Education, Inc.
    10. 10. The Principle of Redox • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions • In oxidation, a substance loses electrons, or is oxidized • In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)© 2011 Pearson Education, Inc.
    11. 11. Figure 9.UN01 becomes oxidized (loses electron) becomes reduced (gains electron)
    12. 12. Figure 9.UN02 becomes oxidized becomes reduced
    13. 13. • The electron donor is called the reducing agent • The electron receptor is called the oxidizing agent • Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds • An example is the reaction between methane and O2© 2011 Pearson Education, Inc.
    14. 14. Figure 9.3 Reactants Products becomes oxidized Energy becomes reduced Methane Oxygen Carbon dioxide Water (reducing (oxidizing agent) agent)
    15. 15. Oxidation of Organic Fuel Molecules DuringCellular Respiration • During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced© 2011 Pearson Education, Inc.
    16. 16. Figure 9.UN03 becomes oxidized becomes reduced
    17. 17. Stepwise Energy Harvest via NAD+ and theElectron Transport Chain • In cellular respiration, glucose and other organic molecules are broken down in a series of steps • Electrons from organic compounds are usually first transferred to NAD+, a coenzyme • As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP© 2011 Pearson Education, Inc.
    18. 18. Figure 9.4 NAD+ NADH Dehydrogenase Reduction of NAD+ (from food) Oxidation of NADH Nicotinamide Nicotinamide (oxidized form) (reduced form)
    19. 19. Figure 9.UN04 Dehydrogenase
    20. 20. • NADH passes the electrons to the electron transport chain • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction • O2 pulls electrons down the chain in an energy- yielding tumble • The energy yielded is used to regenerate ATP© 2011 Pearson Education, Inc.
    21. 21. Figure 9.5 H2 + 1/2 O2 2H + /2 O2 1 (from food via NADH) Controlled release of 2H + 2e + − energy for synthesis of ATP Elec chain ATP Free energy, GFree energy, G tron Explosive ATP release of tran heat and light ATP energy spor 2 e− t 1 /2 O2 2H + H2O H2O (a) Uncontrolled reaction (b) Cellular respiration
    22. 22. The Stages of Cellular Respiration:A Preview • Harvesting of energy from glucose has three stages – Glycolysis (breaks down glucose into two molecules of pyruvate) – The citric acid cycle (completes the breakdown of glucose) – Oxidative phosphorylation (accounts for most of the ATP synthesis)© 2011 Pearson Education, Inc.
    23. 23. Figure 9.UN05 1. Glycolysis (color-coded teal throughout the chapter) 2. Pyruvate oxidation and the citric acid cycle (color-coded salmon) 3. Oxidative phosphorylation: electron transport and chemiosmosis (color-coded violet)
    24. 24. Figure 9.6-1 Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION ATP Substrate-level phosphorylation
    25. 25. Figure 9.6-2 Electrons Electrons carried carried via NADH and via NADH FADH2 Pyruvate Glycolysis Citric oxidation acid Glucose Pyruvate Acetyl CoA cycle CYTOSOL MITOCHONDRION ATP ATP Substrate-level Substrate-level phosphorylation phosphorylation
    26. 26. Figure 9.6-3 Electrons Electrons carried carried via NADH and via NADH FADH2 Oxidative Pyruvate Glycolysis Citric phosphorylation: oxidation acid electron transport Glucose Pyruvate Acetyl CoA cycle and chemiosmosis CYTOSOL MITOCHONDRION ATP ATP ATP Substrate-level Substrate-level Oxidative phosphorylation phosphorylation phosphorylation
    27. 27. • The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions© 2011 Pearson Education, Inc.
    28. 28. • Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration • A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation • For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP© 2011 Pearson Education, Inc.
    29. 29. Figure 9.7 Enzyme Enzyme ADP P Substrate ATP Product
    30. 30. Concept 9.2: Glycolysis harvests chemicalenergy by oxidizing glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases – Energy investment phase – Energy payoff phase • Glycolysis occurs whether or not O2 is present© 2011 Pearson Education, Inc.
    31. 31. Figure 9.8 Energy Investment Phase Glucose 2 ADP + 2 P 2 ATP used Energy Payoff Phase 4 ADP + 4 P 4 ATP formed 2 NAD+ + 4 e− + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 2 Pyruvate + 2 H2O 4 ATP formed − 2 ATP used 2 ATP 2 NAD+ + 4 e− + 4 H+ 2 NADH + 2 H+
    32. 32. Figure 9.9-1 Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate ADP Hexokinase 1
    33. 33. Figure 9.9-2 Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate Fructose 6-phosphate ADP Hexokinase Phosphogluco- isomerase 1 2
    34. 34. Figure 9.9-3 Glycolysis: Energy Investment Phase ATP ATP Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate ADP ADP Hexokinase Phosphogluco- Phospho- isomerase fructokinase 1 2 3
    35. 35. Figure 9.9-4 Glycolysis: Energy Investment Phase ATP ATP Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate ADP ADP Hexokinase Phosphogluco- Phospho- isomerase fructokinase 1 2 3 Aldolase 4 Dihydroxyacetone Glyceraldehyde phosphate 3-phosphate To Isomerase 5 step 6
    36. 36. Figure 9.9-5 Glycolysis: Energy Payoff Phase 2 NADH 2 NAD+ + 2 H+ Triose phosphate 2Pi dehydrogenase 1,3-Bisphospho- 6 glycerate
    37. 37. Figure 9.9-6 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD+ + 2 H+ 2 ADP 2 Triose Phospho- phosphate 2Pi glycerokinase dehydrogenase 1,3-Bisphospho- 7 3-Phospho- 6 glycerate glycerate
    38. 38. Figure 9.9-7 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD+ + 2 H+ 2 ADP 2 2 Triose Phospho- Phospho- phosphate glyceromutase 2Pi glycerokinase dehydrogenase 1,3-Bisphospho- 7 3-Phospho- 8 2-Phospho- 6 glycerate glycerate glycerate
    39. 39. Figure 9.9-8 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 H2O 2 NAD+ + 2 H+ 2 ADP 2 2 2 Triose Phospho- Phospho- Enolase phosphate glyceromutase 2Pi glycerokinase dehydrogenase 9 1,3-Bisphospho- 7 3-Phospho- 8 2-Phospho- Phosphoenol- 6 glycerate glycerate glycerate pyruvate (PEP)
    40. 40. Figure 9.9-9 Glycolysis: Energy Payoff Phase 2 ATP 2 ATP 2 NADH 2 H2O 2 ADP 2 NAD+ + 2 H+ 2 ADP 2 2 2 Triose Phospho- Phospho- Enolase Pyruvate phosphate glyceromutase kinase 2Pi glycerokinase dehydrogenase 9 1,3-Bisphospho- 7 3-Phospho- 8 2-Phospho- Phosphoenol- 10 Pyruvate 6 glycerate glycerate glycerate pyruvate (PEP)
    41. 41. Figure 9.9a Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate Fructose 6-phosphate ADP Hexokinase Phosphogluco- isomerase 1 2
    42. 42. Figure 9.9b Glycolysis: Energy Investment Phase ATP Fructose 6-phosphate Fructose 1,6-bisphosphate ADP Phospho- fructokinase Aldolase 4 3 Dihydroxyacetone Glyceraldehyde phosphate 3-phosphate To Isomerase 5 step 6
    43. 43. Figure 9.9c Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD+ + 2 H+ 2 ADP 2 2 Triose Phospho- phosphate 2Pi glycerokinase dehydrogenase 1,3-Bisphospho- 7 3-Phospho- 6 glycerate glycerate
    44. 44. Figure 9.9d Glycolysis: Energy Payoff Phase 2 ATP 2 H2O 2 ADP 2 2 2 2 Phospho- Enolase Pyruvate glyceromutase kinase 9 3-Phospho- 8 2-Phospho- Phosphoenol- 10 Pyruvate glycerate glycerate pyruvate (PEP)
    45. 45. Concept 9.3: After pyruvate is oxidized, thecitric acid cycle completes the energy-yielding oxidation of organic molecules • In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed© 2011 Pearson Education, Inc.
    46. 46. Oxidation of Pyruvate to Acetyl CoA • Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle • This step is carried out by a multienzyme complex that catalyses three reactions© 2011 Pearson Education, Inc.
    47. 47. Figure 9.10 MITOCHONDRION CYTOSOL CO2 Coenzyme A 1 3 2 NAD+ NADH + H+ Acetyl CoA Pyruvate Transport protein
    48. 48. The Citric Acid Cycle • The citric acid cycle, also called the Krebs cycle, completes the break down of pyrvate to CO2 • The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn© 2011 Pearson Education, Inc.
    49. 49. Figure 9.11 Pyruvate CO2 NAD + CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD+ FAD 3 NADH + 3 H+ ADP + P i ATP
    50. 50. • The citric acid cycle has eight steps, each catalyzed by a specific enzyme • The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate • The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle • The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain© 2011 Pearson Education, Inc.
    51. 51. Figure 9.12-1 Acetyl CoA CoA-SH 1 Oxaloacetate Citrate Citric acid cycle
    52. 52. Figure 9.12-2 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate Citric acid cycle
    53. 53. Figure 9.12-3 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric 3 NADH acid + H+ cycle CO2 α-Ketoglutarate
    54. 54. Figure 9.12-4 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric 3 NADH acid + H+ cycle CO2 CoA-SH α-Ketoglutarate 4 CO2 NAD+ NADH Succinyl + H+ CoA
    55. 55. Figure 9.12-5 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric 3 NADH acid + H+ cycle CO2 CoA-SH α-Ketoglutarate 4 CoA-SH 5 CO2 NAD+ Succinate Pi NADH GTP GDP Succinyl + H+ CoA ADP ATP
    56. 56. Figure 9.12-6 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric 3 NADH acid + H+ cycle CO2 Fumarate CoA-SH α-Ketoglutarate 6 4 CoA-SH FADH2 5 CO2 NAD+ FAD Succinate Pi NADH GTP GDP Succinyl + H+ CoA ADP ATP
    57. 57. Figure 9.12-7 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Malate Citrate Isocitrate NAD+ Citric 3 NADH 7 acid + H+ H2 O cycle CO2 Fumarate CoA-SH α-Ketoglutarate 6 4 CoA-SH FADH2 5 CO2 NAD+ FAD Succinate Pi NADH GTP GDP Succinyl + H+ CoA ADP ATP
    58. 58. Figure 9.12-8 Acetyl CoA CoA-SH NADH + H+ 1 H2O NAD+ 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD+ Citric 3 NADH 7 acid + H+ H2 O cycle CO2 Fumarate CoA-SH α-Ketoglutarate 6 4 CoA-SH FADH2 5 CO2 NAD+ FAD Succinate Pi NADH GTP GDP Succinyl + H+ CoA ADP ATP
    59. 59. Figure 9.12a Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate
    60. 60. Figure 9.12b Isocitrate NAD+ NADH 3 + H+ CO2 CoA-SH α-Ketoglutarate 4 CO2 NAD+ NADH Succinyl + H+ CoA
    61. 61. Figure 9.12c Fumarate 6 CoA-SH FADH2 5 FAD Succinate Pi GTP GDP Succinyl CoA ADP ATP
    62. 62. Figure 9.12d NADH + H+ NAD+ 8 Oxaloacetate Malate 7 H2O Fumarate
    63. 63. Concept 9.4: During oxidativephosphorylation, chemiosmosis coupleselectron transport to ATP synthesis • Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food • These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation© 2011 Pearson Education, Inc.
    64. 64. The Pathway of Electron Transport • The electron transport chain is in the inner membrane (cristae) of the mitochondrion • Most of the chain’s components are proteins, which exist in multiprotein complexes • The carriers alternate reduced and oxidized states as they accept and donate electrons • Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O© 2011 Pearson Education, Inc.
    65. 65. Figure 9.13 NADH 50 2 e− NAD+ FADH2 2 e− FAD Multiprotein Free energy (G) relative to O2 (kcal/mol) 40 FMN I complexes Fe• S II Fe• S Q III Cyt b Fe• S 30 Cyt c1 IV Cyt c Cyt a Cyt a3 20 2 e− 10 (originally from NADH or FADH2) 0 2 H+ + 1/2 O2 H2O
    66. 66. • Electrons are transferred from NADH or FADH2 to the electron transport chain • Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 • The electron transport chain generates no ATP directly • It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts© 2011 Pearson Education, Inc.
    67. 67. Chemiosmosis: The Energy-CouplingMechanism • Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space • H+ then moves back across the membrane, passing through the proton, ATP synthase • ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP • This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work© 2011 Pearson Education, Inc.
    68. 68. Figure 9.14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Catalytic knob ADP + Pi ATP MITOCHONDRIAL MATRIX
    69. 69. Figure 9.15 H+ H + Protein H + complex H+ Cyt c of electron carriers IV Q III I ATP II synth- 2 H+ + 1/2O2 H2O ase FADH2 FAD NADH NAD+ ADP + P i ATP (carrying electrons from food) H+ 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation
    70. 70. • The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis • The H+ gradient is referred to as a proton- motive force, emphasizing its capacity to do work© 2011 Pearson Education, Inc.
    71. 71. An Accounting of ATP Production byCellular Respiration • During cellular respiration, most energy flows in this sequence: glucose → NADH → electron transport chain → proton-motive force → ATP • About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP • There are several reasons why the number of ATP is not known exactly© 2011 Pearson Education, Inc.
    72. 72. Figure 9.16 Electron shuttles MITOCHONDRION span membrane 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Pyruvate oxidation Oxidative Citric phosphorylation: Glucose 2 Pyruvate 2 Acetyl CoA acid electron transport cycle and chemiosmosis + 2 ATP + 2 ATP + about 26 or 28 ATP About Maximum per glucose: 30 or 32 ATP CYTOSOL
    73. 73. Concept 9.5: Fermentation and anaerobicrespiration enable cells to produce ATPwithout the use of oxygen • Most cellular respiration requires O2 to produce ATP • Without O2, the electron transport chain will cease to operate • In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP© 2011 Pearson Education, Inc.
    74. 74. • Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate • Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP© 2011 Pearson Education, Inc.
    75. 75. Types of Fermentation • Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis • Two common types are alcohol fermentation and lactic acid fermentation© 2011 Pearson Education, Inc.
    76. 76. • In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 • Alcohol fermentation by yeast is used in brewing, winemaking, and baking© 2011 Pearson Education, Inc.
    77. 77. Figure 9.17 2 ADP + 2 P 2 ATP 2 ADP + 2 P 2 ATP i i Glucose Glycolysis Glucose Glycolysis 2 Pyruvate 2 NAD + 2 NADH 2 CO2 2 NAD + 2 NADH + 2 H+ + 2 H+ 2 Pyruvate 2 Ethanol 2 Acetaldehyde 2 Lactate (a) Alcohol fermentation (b) Lactic acid fermentation
    78. 78. Figure 9.17a 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD + 2 NADH 2 CO2 + 2 H+ 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation
    79. 79. • In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 • Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt • Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce© 2011 Pearson Education, Inc.
    80. 80. Figure 9.17b 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 NAD + 2 NADH + 2 H+ 2 Pyruvate 2 Lactate (b) Lactic acid fermentation
    81. 81. Comparing Fermentation with Anaerobicand Aerobic Respiration • All use glycolysis (net ATP =2) to oxidize glucose and harvest chemical energy of food • In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis • The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration • Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule© 2011 Pearson Education, Inc.
    82. 82. • Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 • Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration • In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes© 2011 Pearson Education, Inc.

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