1. CAMPBELLBIOLOGYReece Urry Cain Wasserman Minorsky Jackson9 2014 Pearson Education, Inc.TENTHEDITIONCellularRespiration andFermentationLecture Presentation byNicole Tunbridge andKathleen Fitzpatrick

2. Life Is Work Living cells require energy from outside sources Some animals, such as the giraffe, obtain energy by eatingplants, and some animals feed on other organisms that eatplants Energy flows into an ecosystem as sunlight and leaves asheat Photosynthesis generates O2 and organic molecules,which are used in cellular respiration Cells use chemical energy stored in organic molecules togenerate ATP, which powers work 2014 Pearson Education, Inc. 3. Figure 9.2 2014 Pearson Education, Inc.LightenergyOrganicmoleculesPhotosynthesisin chloroplastsCO2 + H2O O2Cellular respirationin mitochondriaECOSYSTEMATP powersmost cellular workATPHeatenergy+ 4. BioFlix: The Carbon Cycle 2014 Pearson Education, Inc. 5. Concept 9.1: Catabolic pathways yield energyby oxidizing organic fuels Catabolic pathways release stored energy bybreaking down complex molecules Electron transfer plays a major role in thesepathways These processes are central to cellular respiration 2014 Pearson Education, Inc. 6. Catabolic Pathways and Production of ATP The breakdown of organic molecules is exergonic Fermentation is a partial degradation of sugarsthat occurs without O2 Aerobic respiration consumes organic moleculesand O2 and yields ATP Anaerobic respiration is similar to aerobicrespiration but consumes compounds otherthan O2 2014 Pearson Education, Inc. 7. Cellular respiration includes both aerobic andanaerobic respiration but is often used to refer toaerobic respiration Although carbohydrates, fats, and proteins are allconsumed as fuel, it is helpful to trace cellularrespiration with the sugar glucoseC6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat) 2014 Pearson Education, Inc. 8. Redox Reactions: Oxidation and Reduction The transfer of electrons during chemical reactionsreleases energy stored in organic molecules This released energy is ultimately used tosynthesize ATP 2014 Pearson Education, Inc. 9. The Principle of Redox Chemical reactions that transfer electronsbetween reactants are called oxidation-reductionreactions, or redox reactions In oxidation, a substance loses electrons,or is oxidized In reduction, a substance gains electrons, or isreduced (the amount of positive charge isreduced) 2014 Pearson Education, Inc. 10. Figure 9.UN01 2014 Pearson Education, Inc.becomes oxidized(loses electron)becomes reduced(gains electron) 11. Figure 9.UN02 2014 Pearson Education, Inc.becomes oxidizedbecomes reduced 12. The electron donor is called the reducing agent The electron receptor is called the oxidizing agent Some redox reactions do not transfer electrons butchange the electron sharing in covalent bonds An example is the reaction between methaneand O2 2014 Pearson Education, Inc. 13. Figure 9.3Reactants ProductsMethane(reducingagent) 2014 Pearson Education, Inc.Oxygen(oxidizingagent)Carbon dioxide Waterbecomes oxidizedbecomes reduced 14. Oxidation of Organic Fuel Molecules DuringCellular Respiration During cellular respiration, the fuel (such asglucose) is oxidized, and O2 is reduced 2014 Pearson Education, Inc. 15. Stepwise Energy Harvest via NAD+ and theElectron Transport Chain In cellular respiration, glucose and other organicmolecules are broken down in a series of steps Electrons from organic compounds are usually firsttransferred to NAD+, a coenzyme As an electron acceptor, NAD+ functions as anoxidizing agent during cellular respiration Each NADH (the reduced form of NAD+)represents stored energy that is tapped tosynthesize ATP 2014 Pearson Education, Inc. 16. NADH passes the electrons to the electrontransport chain Unlike an uncontrolled reaction, the electrontransport chain passes electrons in a series ofsteps instead of one explosive reaction O2 pulls electrons down the chain in an energy-yielding 2014 Pearson Education, Inc.tumble The energy yielded is used to regenerate ATP 17. Figure 9.5H2 + O2 2 H + O2 2014 Pearson Education, Inc.2 e2 H+2 H+ + 2 eH2O O2Controlledrelease ofenergyATPATPATPExplosiverelease(a) Uncontrolled reaction (b) Cellular respirationFree energy, GFree energy, GH2O 18. The Stages of Cellular Respiration: A Preview Harvesting of energy from glucose has threestages Glycolysis (breaks down glucose into twomolecules of pyruvate) The citric acid cycle (completes the breakdown ofglucose) Oxidative phosphorylation (accounts for most ofthe ATP synthesis) 2014 Pearson Education, Inc. 19. Figure 9.UN051.2.3.GLYCOLYSIS (color-coded blue throughout the chapter)PYRUVATE OXIDATION and the CITRIC ACID CYCLE(color-coded orange)OXIDATIVE PHOSPHORYLATION: Electron transport andchemiosmosis (color-coded purple) 2014 Pearson Education, Inc. 20. Figure 9.6-1Electronsvia NADHGLYCOLYSISGlucose PyruvateATP 2014 Pearson Education, Inc.CYTOSOL MITOCHONDRIONSubstrate-level 21. Figure 9.6-2Electronsvia NADHGLYCOLYSIS PYRUVATEGlucose Pyruvate Acetyl CoA CYCLE 2014 Pearson Education, Inc.Electronsvia NADHand FADH2OXIDATION CITRICACIDCYTOSOL MITOCHONDRIONATP ATPSubstrate-level Substrate-level 22. Figure 9.6-3Electronsvia NADHGLYCOLYSIS PYRUVATEGlucose Pyruvate Acetyl CoA 2014 Pearson Education, Inc.Electronsvia NADHand FADH2OXIDATION CITRICACIDCYCLECYTOSOL MITOCHONDRIONOXIDATIVEPHOSPHORYLATION(Electron transportand chemiosmosis)ATP ATP ATPSubstrate-level Substrate-level Oxidative 23. BioFlix: Cellular Respiration 2014 Pearson Education, Inc. 24. The process that generates most of the ATP iscalled oxidative phosphorylation because it ispowered by redox reactions almost 90% of the ATP generated by cellularrespiration A smaller amount of ATP is formed in glycolysisand the citric acid cycle by substrate-levelphosphorylation For each molecule of glucose degraded to CO2 andwater by respiration, the cell makes up to 32molecules of ATP 2014 Pearson Education, Inc. 25. Concept 9.2: Glycolysis harvests chemicalenergy by oxidizing glucose to pyruvate Glycolysis (sugar splitting) breaks down glucoseinto two molecules of pyruvate (10 Step Process) Glycolysis occurs in the cytoplasm and has twomajor phases Energy investment phase Energy payoff phase Glycolysis occurs whether or not O2 is present 2014 Pearson Education, Inc. 26. Figure 9.UN06GLYCOLYSIS 2014 Pearson Education, Inc.PYRUVATEOXIDATIONCITRICACIDCYCLEOXIDATIVEPHOSPHORYL-ATIONATP 27. Figure 9.8Energy Investment Phase 2014 Pearson Education, Inc.GlucoseEnergy Payoff PhaseNet2 ATP used 2 ADP + 2 P4 ADP + 4 P 4 ATP formed2 NAD+ + 4 e + 4 H+ 2 NADH 2 H+2 Pyruvate222222H+ 2 H+44Glucose PyruvateATP formed ATP used ATPH2ONADHNAD+++++ + +2 H2Oe 4 28. Concept 9.3: After pyruvate is oxidized, thecitric acid cycle completes the energy-yieldingoxidation of organic molecules In the presence of O2, pyruvate enters themitochondrion (in eukaryotic cells) where theoxidation of glucose is completed 2014 Pearson Education, Inc. 29. Oxidation of Pyruvate to Acetyl CoA Before the citric acid cycle can begin, pyruvatemust be converted to acetyl Coenzyme A (acetylCoA), which links glycolysis to the citric acid cycle This step is carried out by a multienzyme complexthat catalyses three reactions 2014 Pearson Education, Inc. 30. Figure 9.UN07GLYCOLYSIS 2014 Pearson Education, Inc.PYRUVATEOXIDATIONCITRICACIDCYCLEOXIDATIVEPHOSPHORYL-ATION 31. The Citric Acid Cycle The citric acid cycle, also called the Krebs cycle,completes the break down of pyruvate to CO2 The cycle oxidizes organic fuel derived frompyruvate, generating 1 ATP, 3 NADH, and 1FADH2 per turn 2014 Pearson Education, Inc. 32. The citric acid cycle has eight steps, eachcatalyzed by a specific enzyme The acetyl group of acetyl CoA joins the cycle bycombining with oxaloacetate, forming citrate The next seven steps decompose the citrate backto oxaloacetate, making the process a cycle The NADH and FADH2 produced by the cyclerelay electrons extracted from food to the electrontransport chain 2014 Pearson Education, Inc. 33. Figure 9.UN08GLYCOLYSIS 2014 Pearson Education, Inc.PYRUVATEOXIDATIONCITRICACIDCYCLEOXIDATIVEPHOSPHORYL-ATIONATP 34. Figure 9.12-8 2014 Pearson Education, Inc.Acetyl CoAH2ONADH+ H+OxaloacetateCoA-SHCitrate-KetoglutarateCoA-SHNAD+CO2CO2NAD+NADH+ H+SuccinylCoAGTP GDPATPSuccinateADPFADFADH2FumarateH2OMalateCITRICACIDCYCLE+ H+NAD+P iNADHIsocitrate12564378CoA-SH 35. Concept 9.4: During oxidative phosphorylation,chemiosmosis couples electron transport toATP synthesis Following glycolysis and the citric acid cycle,NADH and FADH2 account for most of the energyextracted from food These two electron carriers donate electrons tothe electron transport chain, which powers ATPsynthesis via oxidative phosphorylation 2014 Pearson Education, Inc. 36. The Pathway of Electron Transport The electron transport chain is in the innermembrane (cristae) of the mitochondrion Most of the chains components are proteins,which exist in multiprotein complexes The carriers alternate reduced and oxidized statesas they accept and donate electrons Electrons drop in free energy as they go down thechain and are finally passed to O2, forming H2O 2014 Pearson Education, Inc. 37. Figure 9.UN09GLYCOLYSIS 2014 Pearson Education, Inc.CITRICACIDCYCLEPYRUVATEOXIDATIONOXIDATIVEPHOSPHORYL-ATIONATP 38. Figure 9.13 2014 Pearson Education, Inc.NADH2 eNAD+FADH22 e FAD FMNI complexesFeSFeSQCyt bFeSCyt c1MultiproteinCyt cCyt aCyt a32 e(originally fromNADH or FADH2)2 H+ + O2H2OIIIIIIV50403020100Free energy (G) relative to O2 (kcal/mol) 39. Electrons are transferred from NADH or FADH2 tothe electron transport chain Electrons are passed through a number ofproteins including cytochromes (each with an ironatom) to O2 The electron transport chain generates no ATPdirectly It breaks the large free-energy drop from food toO2 into smaller steps that release energy inmanageable amounts 2014 Pearson Education, Inc. 40. Chemiosmosis: The Energy-CouplingMechanism Electron transfer in the electron transport chaincauses proteins to pump H+ from the mitochondrialmatrix to the intermembrane space H+ then moves back across the membrane,passing through the protein complex, ATPsynthase ATP synthase uses the exergonic flow of H+ todrive phosphorylation of ATP This is an example of chemiosmosis, the use ofenergy in a H+ gradient to drive cellular work 2014 Pearson Education, Inc. 41. Figure 9.14 2014 Pearson Education, Inc.INTERMEMBRANESPACERotorH+ StatorInternal rodCatalyticknobADP+PiMITOCHONDRIALMATRIXATP 42. Figure 9.15Proteincomplexof electroncarriers(carryingelectronsfromfood) 2014 Pearson Education, Inc.ATPsynthase2 H+ + O2 H2OADP + PiElectron transport chain ChemiosmosisOxidative phosphorylationH+ATPH+H+H+H+Cyt cQIIIIIIIVFADH FAD 2NADH NAD+1 2 43. The energy stored in a H+ gradient across amembrane couples the redox reactions of theelectron transport chain to ATP synthesis The H+ gradient is referred to as a proton-motiveforce, emphasizing its capacity to do work 2014 Pearson Education, Inc. 44. An Accounting of ATP Production by CellularRespiration During cellular respiration, most energy flows inthis sequence:glucose NADH electron transport chain proton-motive force ATP About 34% of the energy in a glucose molecule istransferred to ATP during cellular respiration,making about 32 ATP 2014 Pearson Education, Inc. 45. Figure 9.16Electron shuttlesspan membraneCYTOSOL 2014 Pearson Education, Inc.2 NADHor2 FADH2MITOCHONDRION2 NADH 2 FADH2 6 NADHOXIDATIVEPHOSPHORYLATION(Electron transportand chemiosmosis)CITRICACIDCYCLEPYRUVATEOXIDATION2 Acetyl CoAGLYCOLYSISGlucose 2Pyruvate+ 2 ATP + 2 ATPMaximum per glucose: About30 or 32 ATP+ about 26 or 28 ATP2 NADH 46. Concept 9.5: Fermentation and anaerobicrespiration enable cells to produce ATP withoutthe use of oxygen Most cellular respiration requires O2 to produceATP Without O2, the electron transport chain will ceaseto operate In that case, glycolysis couples with anaerobicrespiration or fermentation to produce ATP 2014 Pearson Education, Inc. 47. Anaerobic respiration uses an electron transportchain with a final electron acceptor other than O2,for example sulfate Fermentation uses substrate-level phosphorylationinstead of an electron transport chain to generateATP 2014 Pearson Education, Inc. 48. Types of Fermentation Fermentation consists of glycolysis plus reactionsthat regenerate NAD+, which can be reused byglycolysis Two common types are alcohol fermentation andlactic acid fermentation 2014 Pearson Education, Inc. 49. In alcohol fermentation, pyruvate is converted toethanol in two steps The first step releases CO2 The second step produces ethanol Alcohol fermentation by yeast is used in brewing,winemaking, and baking 2014 Pearson Education, Inc. 50. Figure 9.172 ADP + 2 P i 2 ATPGlucoseGLYCOLYSIS Glucose2 NAD+ 2 NADH 2014 Pearson Education, Inc.+ 2 H+2 PyruvateCO2 22 Ethanol(a) Alcohol fermentation2 Acetaldehyde 2 Lactate2 ADP + 2 P i 2 ATPGLYCOLYSISNAD+2 2 NADH+ 2 H+Lactic acid fermentation2 Pyruvate(b) 51. In lactic acid fermentation, pyruvate is reducedby NADH, forming lactate as an end product, withno release of CO2 Lactic acid fermentation by some fungi andbacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation togenerate ATP when O2 is scarce 2014 Pearson Education, Inc. 52. Comparing Fermentation with Anaerobic andAerobic Respiration All use glycolysis (net ATP = 2) to oxidize glucoseand harvest chemical energy of food In all three, NAD+ is the oxidizing agent thataccepts electrons during glycolysis 2014 Pearson Education, Inc. 53. The processes have different mechanisms foroxidizing NADH: In fermentation, an organic molecule (such aspyruvate or acetaldehyde) acts as a final electronacceptor In cellular respiration electrons are transferred tothe electron transport chain Cellular respiration produces 32 ATP per glucosemolecule; fermentation produces 2 ATP perglucose molecule 2014 Pearson Education, Inc. 54. Obligate anaerobes carry out fermentation oranaerobic respiration and cannot survive in thepresence of O2 Yeast and many bacteria are facultativeanaerobes, meaning that they can surviveusing either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork inthe metabolic road that leads to two alternativecatabolic routes 2014 Pearson Education, Inc. 55. Figure 9.18 2014 Pearson Education, Inc.GlucoseGlycolysisCYTOSOLPyruvateNo O2 present:FermentationO2 present:Aerobic cellularrespirationEthanol,lactate, orother productsMITOCHONDRIONAcetyl CoACITRICACIDCYCLE 56. The Evolutionary Significance of Glycolysis Ancient prokaryotes are thought to have usedglycolysis long before there was oxygen in theatmosphere Very little O2 was available in the atmosphere untilabout 2.7 billion years ago, so early prokaryoteslikely used only glycolysis to generate ATP Glycolysis is a very ancient process 2014 Pearson Education, Inc. 57. Concept 9.6: Glycolysis and the citric acid cycleconnect to many other metabolic pathways Gycolysis and the citric acid cycle are majorintersections to various catabolic and anabolicpathways 2014 Pearson Education, Inc. 58. The Versatility of Catabolism Catabolic pathways funnel electrons from manykinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids; aminogroups can feed glycolysis or the citric acid cycle 2014 Pearson Education, Inc. 59. Fats are digested to glycerol (used in glycolysis)and fatty acids (used in generating acetyl CoA) Fatty acids are broken down by beta oxidationand yield acetyl CoA An oxidized gram of fat produces more than twiceas much ATP as an oxidized gram of carbohydrate 2014 Pearson Education, Inc. 60. Figure 9.19-1Proteins Carbohydrates FatsAminoacids 2014 Pearson Education, Inc.Sugars Glycerol Fattyacids 61. Figure 9.19-2Proteins Carbohydrates FatsAminoacids 2014 Pearson Education, Inc.Sugars Glycerol FattyacidsGLYCOLYSISGlucoseGlyceraldehyde 3- PNH Pyruvate 3 62. Figure 9.19-3Proteins Carbohydrates FatsAminoacids 2014 Pearson Education, Inc.Sugars Glycerol FattyacidsGLYCOLYSISGlucoseGlyceraldehyde 3- PPyruvateAcetyl CoANH3 63. Figure 9.19-4Proteins Carbohydrates FatsAminoacids 2014 Pearson Education, Inc.Sugars Glycerol FattyacidsGLYCOLYSISGlucoseGlyceraldehyde 3- PPyruvateAcetyl CoACITRICACIDCYCLENH3 64. Figure 9.19-5Proteins Carbohydrates FatsAminoacids 2014 Pearson Education, Inc.Sugars Glycerol FattyacidsGLYCOLYSISGlucoseGlyceraldehyde 3- PPyruvateAcetyl CoACITRICACIDCYCLEOXIDATIVEPHOSPHORYLATIONNH3 65. Biosynthesis (Anabolic Pathways) The body uses small molecules to build othersubstances These small molecules may come directly fromfood, from glycolysis, or from the citric acid cycle 2014 Pearson Education, Inc. 66. Regulation of Cellular Respiration via FeedbackMechanisms Feedback inhibition is the most commonmechanism for metabolic control If ATP concentration begins to drop, respirationspeeds up; when there is plenty of ATP,respiration slows down Control of catabolism is based mainly onregulating the activity of enzymes at strategicpoints in the catabolic pathway 2014 Pearson Education, Inc. 67. Figure 9.20 2014 Pearson Education, Inc.GlucoseAMPStimulatesGLYCOLYSISFructose 6-phosphatePhosphofructokinaseFructose 1,6-bisphosphateInhibits InhibitsCitratePyruvateAcetyl CoAATPCITRICACIDCYCLEOxidativephosphorylation