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09 cellular respiration


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09 cellular respiration

  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. 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.
  7. 7. • 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.
  8. 8. 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.
  9. 9. 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.
  10. 10. Figure 9.UN02 becomes oxidized becomes reduced
  11. 11. 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.
  12. 12. Figure 9.UN03 becomes oxidized becomes reduced
  13. 13. 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.
  14. 14. Figure 9.4 NAD+ NADH Dehydrogenase Reduction of NAD+ (from food) Oxidation of NADH Nicotinamide Nicotinamide (oxidized form) (reduced form)
  15. 15. • 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.
  16. 16. 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
  17. 17. 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.
  18. 18. 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
  19. 19. • 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.
  20. 20. Figure 9.7 Enzyme Enzyme ADP P Substrate ATP Product
  21. 21. Glycolysis harvests chemical energy byoxidizing 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.
  22. 22. 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
  23. 23. 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)
  24. 24. Figure 9.9a Glycolysis: Energy Investment Phase ATP Glucose Glucose 6-phosphate Fructose 6-phosphate ADP Hexokinase Phosphogluco- isomerase 1 2
  25. 25. 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
  26. 26. 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
  27. 27. 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)
  28. 28. After pyruvate is oxidized, the citric acidcycle completes the energy-yieldingoxidation 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.
  29. 29. 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.
  30. 30. Figure 9.10 MITOCHONDRION CYTOSOL CO2 Coenzyme A 1 3 2 NAD+ NADH + H+ Acetyl CoA Pyruvate Transport protein
  31. 31. The Citric Acid Cycle • The citric acid cycle, also called the Krebs cycle or TCA 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.
  32. 32. 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
  33. 33. • 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.
  34. 34. 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
  35. 35. During oxidative phosphorylation,chemiosmosis couples electron transport toATP 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.
  36. 36. 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.
  37. 37. 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
  38. 38. • 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.
  39. 39. 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.
  40. 40. Figure 9.14 INTERMEMBRANE SPACE A rotor within the membrane spins as shown when H+ flows H+ past it down the H+ Stator gradient. Rotor A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, Internal activating catalytic rod sites in the knob. Catalytic knob Three catalytic sites in the stationary knob join inorganic ADP phosphate to ADP to + make ATP. Pi ATP MITOCHONDRIAL MATRIX
  41. 41. 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
  42. 42. • 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.
  43. 43. Proton Motive Force• Is an electrochemical gradient• Two gradients drive the protons from the intermembrane space into the matrix – It is more negative inside the matrix than in the intermembrane space, so there is electric potential across the membrane • H+ is attracted to the opposite negative charge inside the matrix – There is a chemical or pH gradient as well • Greater concentration of H+ in the intermembrane space causes the protons to move to an area of lower concentration inside the matrix• About 85% of the proton motive force is derived from the electric or charge gradient while approximately 15% comes from the chemical gradient
  44. 44. 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© 2011 Pearson Education, Inc.
  45. 45. ATP Synthase• Results from numerous experiments show that, on average, 3 protons have to pass through ATP synthase for 1 ATP to be synthesized• Therefore, 9 protons would be required to produce 3 ATP, and we’ve seen that the electrons from NADH lead to the translocation of 10 protons into the intermembrane space• But, it’s not quite that simple
  46. 46. ATP Synthase• 3 protons produce 1 ATP, but the ATP has to be exported out of the mitochondria since most of them are used in the cytoplasm• Adenine nucleotide translocase exchanges mitochondrial ATP4- for cytosolic ADP3-, but it results in a -1 net charge loss in the matrix• Formation of ATP also requires the import of phosphate through a phosphate transporter• Phosphate (H2PO4-) enters with H+ through an electroneutral symporter• The cost of moving phosphate and ADP in and ATP out is approximately equal to the influx of 1 H+• Thus, synthesis of 1 ATP requires 4 protons
  47. 47. P/O Ratio• Ratio of molecules phosphorylated to atoms of oxygen reduced• 2 electrons are required to reduce a single atom of oxygen• For each pair of electrons that pass through the ETC, 10 protons are translocated across the membrane through ATP synthase• Since 4 protons are needed for each molecule of cytoplasmic ATP, the P/O ratio = 10/4 = 2.5 – This applies to NADH, but the electrons involved in succinate oxidation skip complex I, so 6/4 = 1.5
  48. 48. 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
  49. 49. 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.
  50. 50. 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.
  51. 51. • 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.
  52. 52. 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
  53. 53. • 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.
  54. 54. 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 • Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule© 2011 Pearson Education, Inc.
  55. 55. • 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.
  56. 56. Figure 9.18 Glucose Glycolysis CYTOSOL Pyruvate No O2 present: O2 present: Fermentation Aerobic cellular respiration MITOCHONDRION Ethanol, Acetyl CoA lactate, or other products Citric acid cycle
  57. 57. The Evolutionary Significance of Glycolysis • Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere • Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP • Glycolysis is a very ancient process© 2011 Pearson Education, Inc.
  58. 58. The Versatility of Catabolism • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration • Glycolysis accepts a wide range of carbohydrates • Proteins must be digested to amino acids; after removal of the amino group, the carbon skeleton can be converted into intermediates of glycolysis or the citric acid cycle© 2011 Pearson Education, Inc.
  59. 59. • Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) • Fatty acids are broken down by beta oxidation and yield acetyl CoA • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate© 2011 Pearson Education, Inc.
  60. 60. Figure 9.19 Proteins Carbohydrates Fats Amino Sugars Glycerol Fatty acids acids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation
  61. 61. Biosynthesis (Anabolic Pathways) • The body uses small molecules to build other substances • These small molecules may come directly from food, from glycolysis, or from the citric acid cycle© 2011 Pearson Education, Inc.
  62. 62. Regulation of Cellular Respiration viaFeedback Mechanisms • Feedback inhibition is the most common mechanism for control • If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down • Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway© 2011 Pearson Education, Inc.
  63. 63. Figure 9.20 Glucose AMP Glycolysis Fructose 6-phosphate Stimulates + Phosphofructokinase − − Fructose 1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylation