（生物科技行业）细胞生物学双语教案(线粒体结构与功能)细胞生物学双语教案3（线粒体结构和功能）MitochondrialSubstructureMitochondriacontaintwomembranes,separatedbyaspace.Botharethetypicalunitmembrane(railroadtrack)instructure.Insidethespaceenclosedbytheinnermembraneisthematrix.ThisappearsmoderatelydenseandonemayfindstrandsofDNA,ribosomes,orsmallgranulesinthematrix.Themitochondriaareabletocodeforpartoftheirproteinswiththesemoleculartools.Theabovecartoonshowsthediagramofthemitochondrialmembranesandtheenclosedcompartments.Howaremitochondriaorganizedtobepowerhouses?Thefoodweeatisoxidizedtoproducehigh-energyelectronsthatareconvertedtostoredenergy.Thisenergyisstoredinhighenergyphosphatebondsinamoleculecalledadenosinetriphosphate,orATP.ATPisconvertedfromadenosinediphosphatebyaddingthephosphategroupwiththehigh-energybond.Variousreactionsinthecellcaneitheruseenergy(wherebytheATPisconvertedbacktoADP,releasingthehighenergybond)orproduceit(wherebytheATPisproducedfromADP).Stepsfromglycolysistotheelectrontransportchain.Whyaremitochondriaimportant?LetsbreakdowneachofthestepssoyoucanseehowfoodturnsintoATPenergypacketsandwater.Thefoodweeatmustfirstbeconvertedtobasicchemicalsthatthecellcanuse.Someofthebestenergysupplyingfoodscontainsugarsorcarbohydrates.bread,forexample.Usingthisasanexample,thesugarsarebrokendownbyenzymesthatsplitthemintothesimplestformofsugarwhichiscalledglucose.Then,glucoseentersthecellbyspecialmoleculesinthemembranecalled“glucosetransporters”.Onceinsidethecell,glucoseisbrokendowntomakeATPintwopathways.Thefirstpathwayrequiresnooxygenandiscalledanaerobicmetabolism.Thispathwayiscalledglycolysisanditoccursinthecytoplasmoutsidethemitochondria.Duringglycolysis,glucoseisbrokendownintopyruvate.Otherfoodslikefatscanalsobebrokendownforuseasfuel(seefollowingcartoon).Eachreactionisdesignedtoproducesomehydrogenions(electrons)thatcanbeusedtomakeenergypackets(ATP).However,only4ATPmoleculescanbemadebyonemoleculeofglucoserunthroughthispathway.Thatiswhymitochondriaandoxygenaresoimportant.WeneedtocontinuethebreakdownprocesswiththeKrebscycleinsidethemitochondriainordertogetenoughATPtorunallthecellfunctions.Theeventsthatoccurinsideandoutsidemitochondriaarediagrammedintheabovecartoon.PyruvateiscarriedintothemitochondriaandthereitisconvertedintoAcetylCo-AwhichenterstheKrebscycle.Thisfirstreactionproducescarbondioxidebecauseitinvolvestheremovalofonecarbonfromthepyruvate.HowdoestheKrebscyclework?ThewholeideabehindrespirationinthemitochondriaistousetheKrebscycle(alsocalledthecitricacidcycle)togetasmanyelectronsoutofthefoodweeataspossible.Theseelectrons(intheformofhydrogenions)arethenusedtodrivepumpsthatproduceATP.TheenergycarriedbyATPisthenusedforallkindsofcellularfunctionslikemovement,transport,entryandexitofproducts,division,etc.Thefollowingexplanationisverysimpleandfocusesononlythepathwayfrompyruvatethroughthecycle.However,itillustratestheprocessanditsfunctions.ToruntheKrebscycle,youneedseveralimportantmoleculesinadditiontoalltheenzymes.Consultyourtextfordetailsabouttheenzymesthemselves.Thispresentationwillfocusontheelectrondonors,carriersandacceptors.First,youneedpyruvate,whichismadebyglycolysisfromglucose.Next,youneedsomecarriermoleculesfortheelectrons.Therearetwotypesofthese:oneiscallednicotinamideadeninedinucleotide(NAD+)andtheotheriscalledflavinadeninedinucleotide(FAD+).Thethirdmolecule,ofcourse,isoxygen.Pyruvateisa3carbonmolecule.Afteritentersthemitochondria,itisbrokendowntoa2carbonmoleculebyaspecialenzyme(seetextformoredetailsaboutthebiochemistryofeachstep).Thisreleasescarbondioxide.The2carbonmoleculeiscalledAcetylCoAanditenterstheKrebscyclebyjoiningtoa4carbonmoleculecalledoxaloacetate.Oncethetwomoleculesarejoined,theymakea6carbonmoleculecalledcitricacid(2carbons+4carbons=6carbons).ThatiswheretheCitricacidcyclegotitsname.fromthatfirstreactionthatmakescitricacid.Citricacidisthenbrokendownandmodifiedinastepwisefashion(seetextfordetails)and,asthishappens,hydrogenionsandcarbonmoleculesarereleased.ThecarbonmoleculesareusedtomakemorecarbondioxideandthehydrogenionsarepickedupbyNADandFAD(seebelow).Eventually,theprocessproducesthe4carbonoxaloacetateagain.Thereasontheprocessiscalledacycle,isbecauseitendsupalwayswhereitstarted.withoxaloacetateavailabletocombinewithmoreacetylcoA.Whatis“oxidativephosphorylation”?First,somebasicdefinitions.Whenyoutakehydrogenionsorelectronsawayfromamolecule,you“oxidize”thatmolecule.Whenyougivehydrogenionsorelectronstoamolecule,you“reduce”thatmolecule.Whenyougivephosphatemoleculestoamolecule,you“phosphorylate”thatmolecule.So,oxidativephosphorylation(verysimply)meanstheprocessthatcouplestheremovalofhydrogenionsfromonemoleculeandgivingphosphatemoleculestoanothermolecule.Howdoesthisapplytomitochondria?AstheKrebscycleruns,hydrogenions(orelectrons)aredonatedtothetwocarriermoleculesin4ofthesteps.TheyarepickedupbyeitherNADorFADandthesecarriermoleculesbecomeNADHandFADH(becausetheynowarecarryingahydrogenion).Thefollowingcartoonshowswhathappensnext.Theseelectronsarecarriedchemicallytotherespiratoryorel