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生物化學IILectureFattyacidmetabolismwebversion的學習教案第1頁/共22頁Fattyacidoxidation-energyfromlipidsLongchainFAserveasmainsourceforanimals:FAareoxidizedandbrokendowntoAcCoA.Thereleaseofelectrons(NADH)drivesATPsynthesisEnergyTheproductionofAcCoAfeedstheTCAcycleEnergySourcesofFA:DietCellstorage(lipiddroplets)Synthesis(excesscarbs,etc.)第2頁/共22頁FattyacidoxidationoutlineLipasesareproducedinthepancreas第3頁/共22頁RoleofLipasesBreakdownofTriglyceridesTriglyceridesingestedwaterinsolubleEmulsifiedbybilesalts(detergents)inintestineLipasesbreakthemdowntofattyacidsandglycerolwhicharetakenupbyintestinalmucosaTriglyceridesstoredinadiposetissueBrokendownbylipases,triggeredbyhormonalsignals(epinephrine,glucagon)第4頁/共22頁LipasesR=fattyacidchain(CH2)nCH3第5頁/共22頁BreakdownofphospholipidsbyphospholipasesPhospholipasesA(1and2),C,andD.PhospholipasesimportantforintracellularsignalsEx:InositoltriphosphatefromPhosphotidylinositolwhichisinvolvedinsignallingCa+releasefromER(musclecontraction,otheracitivties)Phospholipasesalsopresentinsnakevenomandwasp/beepoisons第6頁/共22頁β-oxidationSequentialbreakdownoffattyacidstoyieldAcCoAOccursinmitochondria(likeTCA)Seriesof4basicstepsthatarerepeatedoverandoverAcCoAproducedTCAcycleCO2andenergyForaC16wehave7roundsofβ-oxidationtoyield:8AcCoA7NADH7FADH2第7頁/共22頁β-oxidationPalmiticacid(C16):C15H31COOH+2302

16CO2+16H2O ?Go`=-9773KJ/molGlucose(CH2O)6+6O2

6CO2+6H2O ?Go`=-2868KJ/molPalmiticacidhasmanymorecarbonstooxidizeandismuchmorereduced第8頁/共22頁Β-oxidation-transportintomitochondriaThefattyacids,oncetakenupbythecell,mustbetransportedtothemitochondriaFattyAcylCoASynthetaseisboundtomitochondrialoutermembrane第9頁/共22頁SummaryoftransportActivationwithCoASHbyfattyacylCoAsynthetaseTransportacrossmitochondrialINNERmembranebylinkingwithcarnitinebycarnitineacyltransferaseIandremovalbycarnitineacyltransferaseII.Fattyacylesterlinkagehere第10頁/共22頁β-oxidationofstraightchainFAAcylCoAdehase:Has3isoenzymes:Longchain(12-18C)Mediumchain(4-14C)Shortchain(4-8C)Thisisrepeated6moretimestoyield:7AcCoA7NADH7FADH27roundsforaC16Whynot8?Β-ketoacyl-CoAthiolase第11頁/共22頁β-oxidationofstraightchainFAEnergyyield:Activation:-2ATPΒ-oxidation:

7NADH 17.5ATP7FADH2 10.5ATP8AcCoA:24NADH 60ATP8FADH2 12ATP8GTP 8ATPTotal 106ATPOxidationofpalmiticacid:~9800KJ/mol106ATP:energyfromphosphatebonds:106x30.5KJ/mol=3230KJ/molThereforeefficiencyis3230/9800x100%=33%Comparabletoefficiencyinglycolysis第12頁/共22頁β-oxidationofstraightchainFAQuestion:HowmuchmoreATPfromstearicacid?(C18)1moreroundβ-oxidation:1NADH,1FADH21moreAcCoA:3NADH,1FADH2,1GTPTotal=14extraATP第13頁/共22頁β-oxidationofunsaturatedFAMonounsaturatedFA第14頁/共22頁β-oxidationofunsaturatedFAPolyunsaturatedFA:Ex:linoleicacid(cis-?9,cis-?12)Requiresadienoyl-CoAreductase(NADPH)stepaswellasanenoylCoAisomerasestepbeforecontinuingnormalβ-oxidation第15頁/共22頁β-oxidationofodd-numberedfattyacidsNormalβ-oxidationproceedsuntilweareleftwithaC3chainEx:C17willproceedfor7roundsofβ-oxidation…..CO2incorporatedviaBiotin第16頁/共22頁Roleofbiotin…Biotiniscommonlyusediscarboxylationreactionsascofactor:ATPADPBiotinCarboxybiotinPropionylCoAcarboxylaseMethylMalonylCoAPropionylCoACO2第17頁/共22頁Starvation–fateoffattyacidsWhathappenswhenyou’restarving?Runoutofglucose,glycogenstores(diabetics)BodyinitiatesgluconeogenesisGlucoseneededforkeyareas(brain,etc)TCAcycleintermediates(suchasOAA)aredepletedtodothisβ-oxidationinitiated……AcCoAproducedinlargeamountsPotentialproblem?第18頁/共22頁Starvation–fateoffattyacidsExcessAcCoAproducedthatbodycannotmetabolizeLiverconvertsittoacetoacetateandβ-hydroxybutyrateandreleasesitintobloodAcetoacetateusedbyperipheraltissuesforenergyCanleadtoadecreaseinbloodpH–acidosis(commontodiabetics)第19頁/共22頁EnergysourcesforexerciseCreatine:anotherenergycarrierotherthanATPActsasareservoirofphosphorylgroupsWhenATPisdepletedbyrapidexerciseorexertion,creatine-phosphateisusedtoreplenishATPstoresbythereversereactionCreatineisfoundinmanytissues(muscle,heart,brain)andisfoundat~10xtheconcentrationofATPCreatineissynthesizedinliver(orfromexogenoussources:fishandmeat)mostlystoredinmuscle(120to140g/person).第20頁/共22頁ATPsourcesun

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