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1、Chapter26ThebiosynthesisofmembranelipidsandsteroidsFatssuchasthetriacylglycerolmoleculearewildlyusedtostoreexcessenergyforlateruseandtofulfillotherpurposes.26.1PhosphatidateisacommonintermediateinthesynthesisofphospholipidsandtriacylglycerolsGlycerolphosphateacyltransferase.Endoplasm
2、icreticulum/Outermitochondrialmembrane.Diglycerideacyltransferase.Triacylglcerolsynthetasecomplexinliver.26.1.1ThesynthesisofphospholipidsrequiresanactivatedintermediatePhospholipidsynthesis=thecombinationofadiacylglyceridewithanalcoholAnabolicreactionDiacylglyceroloralcoholshouldbea
3、ctivated.SynthesisfromanactivateddiacylglerolStructureofCDP-diacylglycerol.SynthesisformanactivatedalcoholInallofbiosyntheses,anactivatedintermediate(UDP-glucose,CDP-diacylglycerol,CDP-alcohol)isformedfromaphosphorylatedsubstrate(glucose-1-phosphate,phosphatide,phosphorylalcohol)anda
4、nucleosidetriphosphate.Theactivatedintermediatethenreactswithahydroxylgroup(theterminusofglycogen,thesidechainofserine,oradiacylglycerol).26.1.2PlasmalogensandotheretherphospholipidsaresynthesizedfromdihydroxyacetonephosphateSynthesisofanetherphospholipid.26.1.3Sphingolipidsaresynthe
5、sizedfromceramide鞘氨醇Synthesisofsphingolipids.神經酰胺葡萄糖腦苷脂神經節(jié)苷脂鞘磷脂GangliosideGM1.半乳糖唾液酸N-乙酰半乳糖胺葡萄糖26.1.4RespiratorydistresssyndromeandTay-SachsdiseaseresultfromthedisruptionoflipidmetabolismTay-Sachsdisease（泰薩氏幼年黑朦白癡癥）(1)A1-year-oldinfantwithTay-Sachsdisease.(2)Electronmicrographofaport
6、ionofanaffectedbraincell,showingtheabnormalgangliosidedepositsinthelysosomes.26.2CholesterolissynthesizedfromacetylcoenzymeAinthreestagesLabelingofcholesterol.26.2.1Thesynthesisofmevalonate,whichisactivatedasisopentenylpyrophosphate,initiatesthesynthesisofcholesterolFatesof3-hydroxy-
7、3-methylglutarylCoA.二羥甲基戊酸Synthesisofisopentenylpyrophosphate.Squalenesynthesis.異戊二烯基轉移酶焦磷酸牻牛兒酯26.2.2SqualenecyclizestoformcholesterolSqualenecyclization.Oxidosqualenecyclase.Cholesterolformation.26.3ThecomplexregulationofcholesterolbiosynthesistakesplaceatseverallevelsHMG-CoAreducta
8、se.3-hydroxy
