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1、第六章核酸（Sixthchapternucleicacid）SixthchapternucleicacidNucleicacidsaregeneticmaterialIn1868,Miesher.acidisolatedfromthenucleiofpuscellsinSwitzerlandwassolubleinalkalisandnotsolubleindiluteacids.Circumstantialevidence:DNAlevelsareessentiallyconstantindiffer
2、enttypesofcellsatdifferentgrowthstagesofthesamespecies.Directevidence:T2phageDNAinfectedwithE.coliThephageproteinwaslabeledwith35S,infectedwithE.coli,andinfectedwithE.coliby32PlabeledphagenucleicacidThedistributionofDNAandRNA(DNAinthenucleusandRNAoutside
3、thenucleus).Section1chemicalcompositionofnucleicacidsNucleicacidisalinearpolynucleotide,thebasicunitofwhichisnucleotides.Structurelevel:nucleicacidnucleotideNucleosidephosphatePentosebaseTherearetwokindsofpentosethatmakeupnucleicacids:D-riboseandD-2-ribo
4、se.Thus,nucleicacidscanbedividedintotwokinds:RNAandDNAP330Table5-1thebasicchemicalcompositionoftwotypesofnucleicacidsBase1.purinebase:adenineguanine2.pyrimidinebases:cytosine,uracil,thymineP331structureformula3.modifiedbaseThereisalargeamountof5-methylcy
5、tosineinplants.InE.coliphage,5-hydroxymethylcytosineinsteadofC.Rarebase:morethan100species,mostofwhicharemethylatedproducts.DNAconsistsofA,G,C,andTbases.RNAconsistsofA,G,C,andUbases.TwonucleosideNucleotidesarecondensedfrompentoseandbases,C1onthesugarring
6、,orN1ofthepyrimidinebase,ortheN9connectionwiththepurinebase.NucleosidesinnucleicacidsarebetanucleosideP332structuredadeninenucleosidecytosinenucleosideDNA'spentoseis:deoxyriboseRNA'spentoseisriboseThreenucleotidesInnucleoside,pentoseC3andC5hydroxylgroups
7、areesterifiedbyphosphoricacidtoproducenucleotides.1,constitutethenucleotideofDNAandRNAP333,table5-32.IntracellularfreenucleotidesandtheirderivativesNucleoside5'-polyphosphateATP,GTP,CTP,ppppA,ppppGItplaysanimportantroleinenergymetabolism,metabolismandreg
8、ulation.ThecyclicnucleotideCAMP(3,5,-cAMP),cGMP(3,5,-cGMP)Theyactassecondmessengersofthehormoneintheplasmamembrane,andcAMPregulatesglucosemetabolismandlipidmetabolismincells.Nucleoside5'polyphosphate3'-polyphosphatePpGpppp
