生物化学简明教程糖代谢.pptx

生物化学简明教程糖代谢丙酮酸氧化Regulationofthepyruvatedehydrogenasecomplex.Thecomplexisinhibitedbyitsimmediateproducts,NADHandacetylCoA.Thepyruvatedehydrogenasecomponentisalsoregulatedbycovalentmodification.Aspecifickinasephosphorylatesandinactivatespyruvatedehydrogenase,andaphosphataseactivesthedehydrogenasebyremovingthephosphoryl.Thekinaseandthephosphatasealsoarehighlyregulatedenzymes.WhydoesTPPdeficiencyleadprimarilytoneurologicaldisorders?Thenervoussystemreliesessentiallyonglucoseasitsonlyfuel.Incontrast,mostothertissuescanusefatsasasourceoffuelforthecitricacidcycle.Theproductofaerobicglycolysis,pyruvate,canenterthecitricacidcycleonlythroughthepyruvatedehydrogenasecomplex.Arsenitepoisoning.Arseniteinhibitsthepyruvatedehydrogenasecomplexbyinactivatingthedihydrolipoamidecomponentofthetransacetylase.Somesulfhydrylreagents,suchas2,3-dimercaptoethanol,relievetheinhibitionbyformingacomplexwiththearsenitethatcanbeexcreted.三羧酸循环(tricarboxylicacidcycle,TCA)三羧酸循环包含8个步骤：（1）乙酰辅酶A与草酰乙酸缩合形成柠檬酸(2)柠檬酸脱水生成顺乌头酸，然后加水生成异柠檬酸草酰琥珀酸(4)α-酮戊二酸氧化脱羧生成琥珀酰辅酶A琥珀酸脱氢酶延胡索酸CH3CO-SCoA+3NAD++FAD+GDP+H3PO4+2H2Overviewofthecitricacidcycle.Thecitricacidcycleoxidizestwo-carbonunits,producingtwomoleculesofCO2,onemoleculeofGTP,andhighenergyelectronsintheformofNADHandFADH2.Thelinkbetweenglycolysisandthecitricacidcycle.PyruvateproducedbyglycolysisisconvertedintoacetylCoA,thefuelofthecitricacidcycle.1mol葡萄糖在有氧分解时所产生ATPmol数糖有氧分解中能量改变三羧酸循环生物学意义TCA循环是糖、脂肪和蛋白质转化枢纽三羧酸循环代谢调整乙醛酸路径(glyoxylatepathway)Theglyoxylatepathway.Theglyoxylatecycleallowsplantsandsomemicroorganismstogrowonacetatebecausethecyclebypassesthedecarboxylationstepsofthecitricacidcycle.Theenzymesthatpermittheconversionofacetateintosuccinate—isocitratelyaseandmalatesynthase—areboxedinblue.2乙酰CoA+NAD++2H2O乙醛酸路径意义乙醛酸循环路径加入碘乙酸或氟化物糖无氧分解和有氧分解是体内糖分解主要路径，但不是唯一路径。磷酸戊糖路径反应过程三、单糖分子间基团转换6(葡萄糖-6-磷酸)+12NADP++6H2O磷酸戊糖路径调整1、生成NADPH，为细胞各种合成反应提供还原力。NADPH是体内主要供氢体，参加各种生物合成反应。如合成脂肪酸、胆固醇及类固醇激素都需要大量NADPH。2、为DNA、RNA和各种辅酶合成提供核糖-5-磷酸糖原异生作用从丙酮酸转变为糖原过程中,并非完全是糖酵解逆反应,因为糖酵解过程中有三个激酶催化反应是不可逆果糖-6-磷