BIO 1140 Lecture Notes - Lecture 14: Intron, Exon

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 TobuildRNA,a5’→3’sstrand,RNAPolymeraseneedstoseparateDNA,takethe3’→
5’information,andbuildthecomplementary5’→3’strand
 Allnewnucleotidesarebeingbuilt(wearen’tjustreplacingtheTsfortheUs(likemostdo
whiledrawing,asashortcut)
Prokaryotes
Eukaryotes
 Don’thaveanucleus(differentlocation
thantheeukaryotes
 BothstartwithDNA
 BothstartwithDNA
 BothendwithRNA
 Thereisanextrastepto
process/matureyourDNA
Prokaryotes
 WeneedaHoloenzyme(stillRNApolymerase)
 InbacteriathereisonlyoneRNApolymeraseinthewholecellthatdoesallthe
transcription(madeofdifferentsubunits)
 Sigmafactor:oneofthesubunits,onlyrequiredtoinitiatetranscription
 Inadozennucleotides,oncetranscriptionhasbegun,sigmafactordetaches
 SigmafactorcannowgomeetupwithanotherRNApolymeraseatanothertranscription
bindingsiteitcaninitiatetranscriptionelsewhere
 Attheendofthecodingregion,theRNApolymerasedetaches
Eukaryotes
 TherearedifferentRNAPolymerasesthataccomplishdifferenttasks(oneforrRNA,one
fortRNA,oneformRNA)
 RNApolymeraseII:(formRNA)doesn’trequireasigmafactorbut,inordertoinitiate
transcription,weneedalotofdifferentproteinstobindtotheregulatorregiontorecruitthe
polymeraseandinviteittotranscribethegene→TranscriptionInitiationComplex
 First,aproteinbindstoaspecificsequencecalledtheTATAbox→thisproteinrecruits
otherTATAbindingproteins
Responseelements:sequencesjustupstreamoftheTATAbox→TATAboxbindingprotein
recruitsTATAbindingprotein,ifanytranscriptionfactorsrecognizeresponseelements,theybind,
polymerasecannowbindtothestartingsite
 Transcriptionoccursatthecorrectspottoensuretheentiresequenceisreadproperly
 Recruitpolymeraseandlineitupproperlyatthecodingregion
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