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Chapter3TranscriptionContent:一、Somebasicconception1.Gene2.Whenaproteinisneededbyacell,thegeneticcodeforthatproteinmustbereadfromtheDNAandprocessed.Atwostepprocess:（1）Transcription=synthesisofasingle-strandedRNAmoleculeusingtheDNAtemplate(1strandofDNAistranscribed).InEukaryotes,transcriptiontakesplaceinthenucleus.（2）Translation=conversionofamessengerRNAsequenceintotheaminoacidsequenceofapolypeptide(i.e.,proteinsynthesis)Translationtakesplaceonribosomesinthecytosol,oronroughER3.TemplatestrandandnontemplatestrandTemplatestrand:The3’to5’strandofDNAinacodingregionthatservesasthetemplateforRNAsynthesis.TheresultingRNAisacomplementofthetemplatestrand.Nontemplatestrand:The5’to3’strandofDNAinacodingregionthathasnofunctioninproducingtheRNA.IthasthesamesequenceastheinitiallytranscribedRNA,exceptthatThymineintheDNAisUracilintheRNA.Sense/antisense+/-Nontranscribed/transcribedNontemplate/templatecoding/template5.BothstrandsencodegenesmRNA--(messenger)intermediatemoleculesusedfortransferofinformationfromDNAtoprotein.rRNA--(ribosomal)functionalRNAmoleculesthatarecomponentsoftheribosome.tRNA--(transfer)functionalRNAmoleculesthatserveasadaptersintranslation.snRNA--(smallnuclear)functionalRNAmoleculesthatareinvolvedintheremovalofintronsfrompre-mRNAs.scRNA--(smallcytoplasmic小胞浆RNA)functionalRNAmoleculesthatareinvolvedinproteintrafickingwiththecytoplasm.i.e.scRNA参与蛋白质的合成和运输8.HowisanRNAstrandsynthesized?Regulatedbygeneregulatoryelementswithineachgene.DNAunwindsnexttoagene.RNAistranscribed5’to3’fromthetemplate(3’to5’).SimilartoDNAsynthesis,except:RNApolymeraseNoprimerNoproofreadingNTPsinsteadofdNTPs(nodeoxy-)AddsUracil(U)insteadofthymine(T)UnlikeDNAreplication,wewillonlywanttocopyspecificsequencesatspecifictimesinspecificcelltypesWewillneedspecificstartandstopsignalsOnlyonestrandwillbecopied二、TranscriptionintheProkaryoticNucleusThereisonlyoneRNApolymeraseinE.coliResponsibleforthesynthesisofalltypesofRNAWewillfirstlookatthecoreenzymeandthenatthehol
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