Bài giảng Biology - Chapter 9: Cellular Respiration: Harvesting Chemical Energy

Chapter 9Cellular Respiration: Harvesting Chemical EnergyOverview: Life Is WorkLiving cellsRequire transfusions of energy from outside sources to perform their many tasksThe giant pandaObtains energy for its cells by eating plantsFigure 9.1EnergyFlows into an ecosystem as sunlight and leaves as heatLight energyECOSYSTEMCO2 + H2OPhotosynthesisin chloroplastsCellular respirationin mitochondriaOrganicmolecules+ O2ATPpowers most cellular work HeatenergyFigure 9.2Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuelsCatabolic Pathways and Production of ATPThe breakdown of organic molecules is exergonicOne catabolic process, fermentationIs a partial degradation of sugars that occurs without oxygenCellular respirationIs the most prevalent and efficient catabolic pathwayConsumes oxygen and organic molecules such as glucoseYields ATPTo keep workingCells must regenerate ATPRedox Reactions: Oxidation and ReductionCatabolic pathways yield energyDue to the transfer of electronsThe Principle of RedoxRedox reactionsTransfer electrons from one reactant to another by oxidation and reductionIn oxidationA substance loses electrons, or is oxidizedIn reductionA substance gains electrons, or is reducedExamples of redox reactionsNa + Cl Na+ + Cl–becomes oxidized(loses electron)becomes reduced(gains electron)Some redox reactionsDo not completely exchange electronsChange the degree of electron sharing in covalent bondsCH4HHHHCOOOOOCHHMethane(reducingagent) Oxygen(oxidizingagent) Carbon dioxide Water+2O2CO2+Energy+2 H2Obecomes oxidizedbecomes reducedReactantsProductsFigure 9.3Oxidation of Organic Fuel Molecules During Cellular RespirationDuring cellular respirationGlucose is oxidized and oxygen is reducedC6H12O6 + 6O2 6CO2 + 6H2O + Energybecomes oxidizedbecomes reducedStepwise Energy Harvest via NAD+ and the Electron Transport ChainCellular respirationOxidizes glucose in a series of stepsElectrons from organic compoundsAre usually first transferred to NAD+, a coenzymeNAD+HOOOO–OOO–OOOPPCH2CH2HOOHHHHOOHHOHHN+CNH2HNHNH2NNNicotinamide(oxidized form)NH2+2[H](from food)DehydrogenaseReduction of NAD+Oxidation of NADH2 e– + 2 H+2 e– + H+NADHOHHNC+Nicotinamide(reduced form)NFigure 9.4NADH, the reduced form of NAD+Passes the electrons to the electron transport chainIf electron transfer is not stepwiseA large release of energy occursAs in the reaction of hydrogen and oxygen to form water(a) Uncontrolled reactionFree energy, GH2OExplosiverelease ofheat and lightenergyFigure 9.5 AH2 + 1/2 O2The electron transport chainPasses electrons in a series of steps instead of in one explosive reactionUses the energy from the electron transfer to form ATP2 H1/2 O2(from food via NADH)2 H+ + 2 e–2 H+2 e–H2O1/2 O2Controlled release of energy for synthesis ofATPATPATPATPElectron transport chain Free energy, G(b) Cellular respiration+Figure 9.5 BThe Stages of Cellular Respiration: A PreviewRespiration is a cumulative function of three metabolic stagesGlycolysisThe citric acid cycleOxidative phosphorylationGlycolysisBreaks down glucose into two molecules of pyruvateThe citric acid cycleCompletes the breakdown of glucoseOxidative phosphorylationIs driven by the electron transport chainGenerates ATPAn overview of cellular respirationFigure 9.6Electronscarriedvia NADHGlycolsisGlucosePyruvateATPSubstrate-levelphosphorylationElectrons carried via NADH and FADH2Citric acid cycleOxidativephosphorylation:electron transport andchemiosmosis ATPATPSubstrate-levelphosphorylationOxidativephosphorylationMitochondrionCytosolBoth glycolysis and the citric acid cycleCan generate ATP by substrate-level phosphorylationFigure 9.7EnzymeEnzymeATPADPProductSubstrateP+Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvateGlycolysisMeans “splitting of sugar”Breaks down glucose into pyruvateOccurs in the cytoplasm of the cellGlycolysis consists of two major phasesEnergy investment phaseEnergy payoff phaseGlycolysisCitricacidcycleOxidativephosphorylationATPATPATP2 ATP4 ATPusedformedGlucose2 ATP + 2 P4 ADP + 4P2 NAD+ + 4 e- + 4 H +2 NADH+ 2 H+2 Pyruvate + 2 H2OEnergy investment phaseEnergy payoff phaseGlucose2 Pyruvate + 2 H2O4 ATP formed – 2 ATP used2 ATP2 NAD+ + 4 e– + 4 H +2 NADH+ 2 H+Figure 9.8A closer look at the energy investment phaseDihydroxyacetonephosphateGlyceraldehyde-3-phosphateHHHHHOHOHHOHOCH2OHHHHHOHOHHOOHPCH2OPHOHHOHOHHOCH2OHPOCH2OCH2OPHOHHOHOHOPCH2COCH2OHHCCHOHCH2OOPATPADPHexokinaseGlucoseGlucose-6-phosphateFructose-6-phosphateATPADPPhosphoglucoisomerasePhosphofructokinaseFructose-1, 6-bisphosphateAldolaseIsomeraseGlycolysis12345CH2OHOxidativephosphorylationCitricacidcycleFigure 9.9 AA closer look at the energy payoff phase2 NAD+NADH2+ 2 H+Triose phosphatedehydrogenase2P i2PCCHOHOPOCH2O2O–1, 3-Bisphosphoglycerate2 ADP2 ATPPhosphoglycerokinaseCH2OP2CCHOH3-PhosphoglyceratePhosphoglyceromutaseO–CCCH2OHHOP2-Phosphoglycerate2 H2O2O–EnolaseCCOPOCH2Phosphoenolpyruvate2 ADP2 ATPPyruvate kinaseO–CCOOCH32687910PyruvateOFigure 9.8 BConcept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic moleculesThe citric acid cycleTakes place in the matrix of the mitochondrionBefore the citric acid cycle can beginPyruvate must first be converted to acetyl CoA, which links the cycle to glycolysisCYTOSOLMITOCHONDRIONNADH+ H+NAD+231CO2Coenzyme APyruvateAcetyle CoASCoACCH3OTransport proteinO–OOCCCH3Figure 9.10An overview of the citric acid cycleATP2 CO23 NAD+3 NADH+ 3 H+ADP + P iFADFADH2CitricacidcycleCoACoA Acetyle CoA NADH+ 3 H+CoACO2Pyruvate(from glycolysis,2 molecules per glucose)ATPATPATPGlycolysisCitricacidcycleOxidativephosphorylationFigure 9.11A closer look at the citric acid cycleFigure 9.12Acetyl CoANADHOxaloacetateCitrateMalateFumarateSuccinateSuccinylCoAa-Ketoglutarate IsocitrateCitricacidcycleSCoACoASHNADHNADHFADH2FADGTPGDPNAD+ADPP iNAD+CO2CO2CoASHCoASHCoASH2O+ H++ H+H2OCCH3OOCCOO–CH2COO–COO–CH2HOCCOO–CH2COO–COO–COO–CH2HCCOO–HOCHCOO–CHCH2COO–HOCOO–CHHCCOO–COO–CH2CH2COO–COO–CH2CH2COCOO–CH2CH2COCOO–12345678GlycolysisOxidativephosphorylationNAD++ H+ATPCitricacidcycleFigure 9.12Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesisNADH and FADH2Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylationThe Pathway of Electron TransportIn the electron transport chainElectrons from NADH and FADH2 lose energy in several stepsAt the end of the chainElectrons are passed to oxygen, forming waterH2OO2NADHFADH2FMNFe•SFe•SFe•SOFADCyt bCyt c1Cyt cCyt aCyt a32 H + + 12IIIIIIIVMultiproteincomplexes01020304050Free energy (G) relative to O2 (kcl/mol)Figure 9.13Chemiosmosis: The Energy-Coupling MechanismATP synthaseIs the enzyme that actually makes ATPINTERMEMBRANE SPACEH+H+H+H+H+H+H+H+P i+ADPATPA rotor within the membrane spins clockwise whenH+ flows past it down the H+ gradient.A stator anchoredin the membraneholds the knobstationary.A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. MITOCHONDRIAL MATRIXFigure 9.14At certain steps along the electron transport chainElectron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane spaceThe resulting H+ gradientStores energyDrives chemiosmosis in ATP synthaseIs referred to as a proton-motive forceChemiosmosisIs an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular workChemiosmosis and the electron transport chainOxidativephosphorylation.electron transportand chemiosmosisGlycolysisATPATPATPInnerMitochondrialmembraneH+H+H+H+H+ATPP iProtein complexof electron carnersCyt cIIIIIIIV(Carrying electronsfrom, food)NADH+FADH2NAD+FAD+2 H+ + 1/2 O2H2OADP +Electron transport chainElectron transport and pumping of protons (H+),which create an H+ gradient across the membraneChemiosmosisATP synthesis powered by the flowOf H+ back across the membraneATPsynthaseQOxidative phosphorylationIntermembranespaceInnermitochondrialmembraneMitochondrialmatrixFigure 9.15An Accounting of ATP Production by Cellular RespirationDuring respiration, most energy flows in this sequenceGlucose to NADH to electron transport chain to proton-motive force to ATPThere are three main processes in this metabolic enterpriseElectron shuttlesspan membraneCYTOSOL2 NADH2 FADH22 NADH6 NADH 2 FADH22 NADHGlycolysisGlucose2Pyruvate2AcetylCoACitricacidcycleOxidativephosphorylation:electron transportandchemiosmosisMITOCHONDRIONby substrate-levelphosphorylationby substrate-levelphosphorylationby oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol Maximum per glucose:About36 or 38 ATP+ 2 ATP+ 2 ATP+ about 32 or 34 ATPorFigure 9.16About 40% of the energy in a glucose moleculeIs transferred to ATP during cellular respiration, making approximately 38 ATPConcept 9.5: Fermentation enables some cells to produce ATP without the use of oxygenCellular respirationRelies on oxygen to produce ATPIn the absence of oxygenCells can still produce ATP through fermentationGlycolysisCan produce ATP with or without oxygen, in aerobic or anaerobic conditionsCouples with fermentation to produce ATPTypes of FermentationFermentation consists ofGlycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysisIn alcohol fermentationPyruvate is converted to ethanol in two steps, one of which releases CO2During lactic acid fermentationPyruvate is reduced directly to NADH to form lactate as a waste product2 ADP + 2P12 ATPGlycolysisGlucose2 NAD+2 NADH2 Pyruvate2 Acetaldehyde 2 Ethanol(a) Alcohol fermentation2 ADP + 2P12 ATPGlycolysisGlucose2 NAD+2 NADH2 Lactate(b) Lactic acid fermentationHHOHCH3C O –OCCOCH3HCOCH3O–COCOCH3OCOCOHHCH3CO22Figure 9.17Fermentation and Cellular Respiration ComparedBoth fermentation and cellular respirationUse glycolysis to oxidize glucose and other organic fuels to pyruvateFermentation and cellular respirationDiffer in their final electron acceptorCellular respirationProduces more ATPPyruvate is a key juncture in catabolismGlucoseCYTOSOLPyruvateNo O2 presentFermentationO2 present Cellular respirationEthanolor lactateAcetyl CoAMITOCHONDRIONCitricacidcycleFigure 9.18The Evolutionary Significance of GlycolysisGlycolysisOccurs in nearly all organismsProbably evolved in ancient prokaryotes before there was oxygen in the atmosphereConcept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathwaysThe Versatility of CatabolismCatabolic pathwaysFunnel electrons from many kinds of organic molecules into cellular respirationThe catabolism of various molecules from foodAmino acidsSugarsGlycerolFattyacidsGlycolysisGlucoseGlyceraldehyde-3- PPyruvateAcetyl CoANH3CitricacidcycleOxidativephosphorylationFatsProteinsCarbohydratesFigure 9.19Biosynthesis (Anabolic Pathways)The bodyUses small molecules to build other substancesThese small moleculesMay come directly from food or through glycolysis or the citric acid cycleRegulation of Cellular Respiration via Feedback Mechanisms Cellular respirationIs controlled by allosteric enzymes at key points in glycolysis and the citric acid cycleThe control of cellular respirationGlucoseGlycolysisFructose-6-phosphatePhosphofructokinaseFructose-1,6-bisphosphateInhibitsInhibitsPyruvateATPAcetyl CoACitricacidcycleCitrateOxidativephosphorylationStimulatesAMP+––Figure 9.20