扬州大学：《生物化学 Biochemistry》课程教学课件（讲稿）chapter15 Oxidative Phosphorylation Free Energy of Electron Transfer

OxidativePhosphorylationFree Energy of Electron Transfer

Oxidative Phosphorylation Free Energy of Electron Transfer

Introduction· Living cells save up metabolic energy predominantlyintheform offats and carbohydrates.. They “spend" this energy for biosynthesis, membranetransport, and movement.? In both directions, energy is exchanged andtransferred in the form of ATP

Introduction • Living cells save up metabolic energy predominantly in the form of fats and carbohydrates. • They “spend” this energy for biosynthesis, membrane transport, and movement. • In both directions, energy is exchanged and transferred in the form of ATP

Introduction· Glycolysis and the TCA cycle convert some of the energy available fromstored and dietary sugars directly toATP? However, most of the metabolic energy that is obtainable from substratesentering glycolysis and the TCA cycle is funneled via oxidation-reductionreactions into NADH and FADH,.The cells oxidize NADH and FADH, and convert their reducing potentialinto the chemical energy of ATP, which is named as OxidativePhosphorylation

Introduction • Glycolysis and the TCA cycle convert some of the energy available from stored and dietary sugars directly to ATP. • However, most of the metabolic energy that is obtainable from substrates entering glycolysis and the TCA cycle is funneled via oxidation-reduction reactions into NADH and FADH2. • The cells oxidize NADH and FADH2 and convert their reducing potential into the chemical energy of ATP, which is named as Oxidative Phosphorylation

An Overview: Electron Transport: Electrons carried byreduced coenzymes (NADH and FADH)are passed through a chain of proteins andcoenzymes to drive the generation of aproton gradient across the innermitochondrialmembranePhosphorylation: The proton gradientruns downhill to drive the synthesis ofATP.It all happens in or at the innermitochondrialmembrane

An Overview • Electron Transport: Electrons carried by reduced coenzymes (NADH and FADH2) are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane. • Phosphorylation: The proton gradient runs downhill to drive the synthesis of ATP. • It all happens in or at the inner mitochondrial membrane

Defining Ox-PhosOxidative>Process that involves electron extraction.> Electrons passed through ETS and ultimately to terminalelectron acceptor.>Generates energy and pumps protons.Phosphorylation> Synthesis ofATPfromADP+P;> Converts energy stored as proton gradient into energy storedinchemical bondV This is in contrast to substrate-level phosphorylation(as in glycolysis)

Defining Ox-Phos  Oxidative  Process that involves electron extraction.  Electrons passed through ETS and ultimately to terminal electron acceptor.  Generates energy and pumps protons.  Phosphorylation  Synthesis of ATP from ADP + Pi  Converts energy stored as proton gradient into energy stored in chemical bond  This is in contrast to substrate-level phosphorylation (as in glycolysis)

BIOPOLYMERSProteinsNucleicacidsPolysaccharidesTriacylglycerolsRecoveringEnergyMONOMERSAminoacidsOxidative phosphorylationNucleotidesMonosaccharidesFattyacids> Converting electron energy into ATPNHIndirectlycoupledNADNADNADHNADHQ>Very efficient recovery of energy2-and3-CarbonINTERMEDIATES Last phase of extracting energy out of biomoleculescitricphoto-NAD*,Qacidsynthesis>FollowtheelectronscycleCONADH,QH2ADP.oxidativephosphorylationH,ONAD*,Q

Recovering Energy  Oxidative phosphorylation  Converting electron energy into ATP  Indirectly coupled  Very efficient recovery of energy  Last phase of extracting energy out of biomolecules  Follow the electrons

Redox ThermodynamicsOxidation is loss; reduction is gainIf you extract electrons from one donor, you must deposit them on acceptorFAD + QH2FADH, + Q个reducedReducedoxidizedoxidizedReactioncanbeexpressedashalf-reactions> Only look at one substance at a timeQH2>Q+2H++2e←→

Redox Thermodynamics  Oxidation is loss; reduction is gain  If you extract electrons from one donor, you must deposit them on acceptor  FADH2 + Q ←→ FAD + QH2 Reduced oxidized oxidized reduced  Reaction can be expressed as half-reactions  Only look at one substance at a time  Q + 2H+ + 2 e- ←→ QH2

RedoxThermodynamicsStandard reduction potential, EoTendency ofthe oxidized form to be reduced (accept electrons)The more + the value, the greater the tendencyActual reduction potential depends on concentrations of speciesR is gas constant (8.3145 J/K/mol)ARTeducedE=ET is temp (Kelvin)nF[Aoxidied]n=number of electronstransferredF is Faraday's constant (96,485 J/V/mol)

Redox Thermodynamics  Standard reduction potential, E0’  Tendency of the oxidized form to be reduced (accept electrons)  The more + the value, the greater the tendency  Actual reduction potential depends on concentrations of species R is gas constant (8.3145 J/K/mol) T is temp (Kelvin) n = number of electrons transferred F is Faraday’s constant (96,485 J/V/mol)

[Areduced0.026 VE=EoInNernstequation[Aoxidized]nAt 25°C(298K):Reductionpotentialpredicts flow ofelectronsFlow from substance with lower to higher potentialLower or negative reduction potential means it is more likely todonatethanreceiveelectrons

Nernst equation At 25℃ (298K):  Reduction potential predicts flow of electrons  Flow from substance with lower to higher potential  Lower or negative reduction potential means it is more likely to donate than receive electrons

FreeEnergy ChangesReductionpotentialpredictsflowofelectronsExample: eflow from NADH (-0.315) to Q(+0.0045)Net:TABLE15-1StandardReductionPotentialsofSomeBiological SubstancesAE=E%(e-acceptor)-E)(e-donor)Half-reaction(V)*1O,+2H+2=H00.815=0.045V-(-0.315V)SO+2H*+2=SO,+H,O0.48NO,+2H*+2c=NO,+H,O0.42=+0.360Cytochrome a, (Fe)+cytochromea, (Fe*t)0.3850.29Cytochromea(Fe)+=cytochromea(Fe)0.235Cytochrome c(Fe") +cytochromee(Fe*")0.22Cytochromen(Fe")+cytochrome(Fe2")HighestEo:O2Cytochromeh(Ft)+tcochmme.b(F2(mitochandrial)0.0770.045Ubiguinone+2H+2ubiguinol0.031Fumarate +2H+2succinateFAD+2H+2FADH, (in faoprotein)~0.0.166Oxaloacetate+2H*+2emalatePyruvate+2H+2=lactate0.185Acetaldchyde +2H*+2=ethanol0.197S+2H*+2=HS0.23Lipoic acid +2H' +2 = dihydrolipoicacid-0.29NAD'+H+2=NADH-0.315

Free Energy Changes Reduction potential predicts flow of electrons Example: e- flow from NADH (-0.315) to Q (+0.0045)