Cellular Respiration Stage 4: Electron Transport Chain

Cellular respirationCellular RespirationStage 4:Electron Transport Chain2006-2007ATP accounting so far Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need toThere is a better way! Electron Transport Chain series of proteins built intoinner mitochondrial membrane along cristae transport proteins & enzymesextract more energy than 4 ATP!There’s got to be a better way!transport of electrons down ETC linked topumping of H to create H gradient yields 36 ATP from 1 glucose! only in presence of O2 (aerobic respiration) O2A working muscle recycles over10 million ATPs per secondMitochondria Double membrane outer membraneinner membrane highly folded cristaeElectron Transport Chain The electron transport chain occurs in enzymes & transportproteins intermembrane space electron carriers found in the innermitochondrial membrane.Electrons pass down electron transportchain in a series of redox reactionsEx. Old time bucket brigade. fluid-filled spacebetween membranes1

Electron Trasport The electrons entering the chain areElectron Transport Chain Complex IV accepts electrons fromhigh energy Complex I accepts NADH Complex II Accepts FADH2 Complex I and II produce Ubiquinone (substrate of complex III)Complex III accepts electrons fromreduced ubiquinone and passes it toCychrome C. Cytochrome C and uses it to makewater in the process (reducesmolecular oxygen)O2 is final electron acceptor.End of chain electrons arepassed on to oxygen to formwaterNADH50Free energy (G) relative to O2 (kcl/mol)FADH240IFMNFe SMultiproteincomplexesFADFe S IIOIIICyt bFe S30Cyt c1IVCyt cCyt aCyt a320102 H 1 2 O20Figure 9.13H2OElectron Transport ChainRemember the Electron Carriers?InnermitochondrialmembraneIntermembrane spaceIIGlycolysisKrebs cycleG3P2 NADHCglucose8 NADH2 FADH2QIIIIIVMitochondrial matrix2

Electron Transport ChainNADH NAD epBuilding proton gradient! HintermembranespaceH H H e- H H IIe–NADH HFAD2H NAD 12O2IIIH2OH cleaved off NADH & FADH2electrons stripped from H atoms H (protons) electrons passed from one electron carrier to next inmitochondrial membrane (ETC) flowing electrons energy to do worke–HI e–FADH2 innermitochondrialmembraneCQStripping H from Electron Carriers Electron carriers pass electrons & H to ETCtransport proteins in membrane pump H (protons)across inner membrane to intermembrane spaceH TA-DA!!Moving electronsdo the work! HH HH What powers the proton(H )But what “pulls” theelectrons down the ETC? H H H H H H Ce–NADHQe–FADH2FADe–2H NAD Ipumps? H IIIVmitochondrialmatrix HH III12O2H 2OIVADP PiATPH Electrons flow downhill Electrons move in steps fromcarrier to carrier downhill to oxygeneach carrier more electronegativecontrolled oxidation controlled release of energy H2OWe getenergyproductioninsteadof fire!O2electronsflow downhillto O2oxidative phosphorylation“proton-motive” forceWe did it! Set up a H H H H gradientAllow the protonsto flow throughATP synthaseSynthesizes ATPADP Pi ATPAll of this depends on therebeing ADP and phosphatein the mitochondrial matrix!H H H H H Chemiosmosis Electron chain stablishes a proton gradient Some energy is used to move protons (H )across a membrane. Protons move across inner mitochondrialmembrane into intermembrane space. Inner mitochondrial separates high protonconcentration with low protonconcentration.ADP PiATPH 3

Chemiosmosis Complexes I, III, and IV move H across the membrane.Diffussion of Protons from high {H}area to low {H} area is limited by ATPsynthase (complex V)H provides energy for the formation ofADP Pi to produce ATP. Pyruvate transported intomitochondriaLink Reaction Krebs (in matrix) ETC (cristae) ADP and Pi are pumped back into thematrix! Chemiosmosis and theelectron transport ation.electron transportand chemiosmosisGlycolysisThere are three main processes inthis metabolic enterpriseElectron shuttlesspan membraneCYTOSOLMITOCHONDRION2 NADHor2 FADH2ATPATPATPH H 2 NADHH IntermembranespaceProtein complexof electroncarnersQMitochondrialmatrixFigure 9.152Pyruvate2AcetylCoA6 NADHCitricacidcycleIV2 FADH2Oxidativephosphorylation:electron transportandchemiosmosisIIIATPsynthaseIIFADH2NADH 2 NADHGlycolysisGlucoseIInnermitochondrialmembraneH Cyt cNAD FAD 2 H 1/2 O2H 2OADP (Carrying electronsfrom, food)ATPPi 2 ATPby substrate-levelphosphorylation 2 ATP about 32 or 34 ATPby substrate-level by oxidative phosphorylation, dependingon which shuttle transports electronsphosphorylationfrom NADH in cytosolH ChemiosmosisElectron transport chainElectron transport and pumping of protons (H ), ATP synthesis powered by the flowwhich create an H gradient across the membrane Of H back across the membraneOxidative phosphorylationMaximum per glucose:About36 or 38 ATPFigure 9.164

1961 1978ChemiosmosisPeter Mitchell Proposed chemiosmotic hypothesis The diffusion of ions across a membrane build up of proton gradient just so H could flowthrough ATP synthase enzyme to build ATP revolutionary idea at the timeChemiosmosislinks the ElectronTransport Chainto ATP synthesisproton motive force1920-1992Pyruvate fromcytoplasmInner mitochondrial HmembraneH IntermembranespaceQNADHAcetyl-CoA1. Electrons are harvestedand carried to thetransport system.NADHKrebscyclee-e-FADH22. Electronsprovide energyto pumpprotons acrossthe membrane.H e-H2Oe- 3. Oxygen joins1 O2 22H with protons toform water.O2H CO2ATPMitochondrialmatrixCellular respirationElectrontransportC systemH ATPATP4. Protons diffuse back indown their concentrationgradient, driving thesynthesis of ATP.ATPsynthase2 ATP 2 ATP 36 ATPSummary of cellular respiration: Onyour own paper—by end of classC6H12O6 6O2 6CO2 6H2O 40 ATP Where did the glucose come from?Where did the O2 come from?Where did the CO2 come from?Where did the CO2 go?Where did the H2O come from?Where did the ATP come from?What else is produced that is not listedin this equation? Why do we breathe?5

Cellular Respiration Stage 4: Electron Transport Chain Cellular respiration ATP accounting so far Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! A working muscle recycles over 10 million ATPs per second