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1、8885d_c21_787-8322/26/049:35AMPage787mac76mac76:385_reb:chapter21LIPIDBIOSYNTHESIS21.1BiosynthesisofFattyAcidsandEicosanoids787Wefirstdescribethebiosynthesisoffattyacids,the21.2BiosynthesisofTriacylglycerols804primarycomponentsofbothtriacylglycerolsandphos-pholipids,thenexaminet
2、heassemblyoffattyacidsinto21.3BiosynthesisofMembranePhospholipids808triacylglycerolsandthesimplermembranephospho-21.4BiosynthesisofCholesterol,Steroids,andlipids.Finally,weconsiderthesynthesisofcholesterol,Isoprenoids816acomponentofsomemembranesandtheprecursorofsteroidssuchasthe
3、bileacids,sexhormones,andadrenocorticalhormones.Howthedivisionof“spoils”cameaboutIdonotrecall—itmayhavebeenbydrawinglots.Atanyrate,DavidShemin21.1BiosynthesisofFattyAcids“drew”aminoacidmetabolism,whichledtohisclassicalandEicosanoidsworkonhemebiosynthesis.DavidRittenburgwastocont
4、inuehisinterestinproteinsynthesisandturnover,Afterthediscoverythatfattyacidoxidationtakesplaceandlipidsweretobemyterritory.bytheoxidativeremovalofsuccessivetwo-carbon(acetyl-CoA)units(seeFig.17–8),biochemiststhought—KonradBloch,onhowhiscareerturnedtoproblemsoflipidthebiosynthesi
5、soffattyacidsmightproceedbyasim-metabolismafterthedeathofhismentor,RudolfSchoen-plereversalofthesameenzymaticsteps.However,asheimer;articleinAnnualReviewofBiochemistry,1987theyweretofindout,fattyacidbiosynthesisandbreak-downoccurbydifferentpathways,arecatalyzedbydif-ipidsplayava
6、rietyofcellularroles,someonlyre-ferentsetsofenzymes,andtakeplaceindifferentpartsLcentlyrecognized.Theyaretheprincipalformofofthecell.Moreover,biosynthesisrequiresthepartici-storedenergyinmostorganismsandmajorconstituentspationofathree-carbonintermediate,malonyl-CoA,ofcellularmem
7、branes.Specializedlipidsserveaspig-thatisnotinvolvedinfattyacidbreakdown.ments(retinal,carotene),cofactors(vitaminK),deter-Wefocusfirstonthepathwayoffattyacidsynthe-gents(bilesalts),transporters(dolichols),hormonessis,thenturnourattentiontoregulationofthepathway(vitaminDderivati
8、ves,sexhormones),extracellularandandtothebiosyn
