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MOLECULAR BIO REVIEW IIIEUKARYOTIC TRANSCRIPTIONTypes of RNA Polymerase in Eukaryotic Systems1RNA Polymerase I located in the nucleolus synthesizes precursor of most rRNAs 2RNA Polymerase II located in the nucleoplasm synthesized mRNA precursors snRNAs3RNA Polymerase III located in the nucleoplasm synthesizes precursors of 5S rRNA tRNAs and small nuclear and cytosolic RNAsTypes of RNA in Eukaryotic Systems1mRNAcode for the synthesis of proteins2rRNAcontribute to the structure of the ribosome3 tRNAplay an important role in translation for carrying amino acids4snRNA involved in the RNA splicing process5snoRNAplay a role in rRNA maturationcovalent modification 6miRNA and siRNAhelp regulate gene expression7ncRNAinvolved in telomere synthesis and xchromosome inactivationRNA Polymerase II StructureFunction Relationship highlighted are the different domains of RNA polymerase II synthesis occurs inside the hollow core of the enzyme CLAMPmobile arm that holds DNA in place RUDDERseparate strands of DNA LIDwhere newly transcribed RNA molecule exits the enzyme the RNA polymerase has a long Cterminal domain 500650 Angstroms contains a conserved heptameric motif ProThrSerProSerTyrSer Note that repeat is TyrSerProThrSerProser extension of CTD coincides with onset of transcriptional elongation for CTD to be extended it must be phosphorylated TRANSCRIPTIONAL MACHINERY an assembly of multiple protein subunits that cooperate with each other to synthesize the mRNAGeneral Transcription Factors1help position RNA polymerase correctly at the promoter needed at all promoters transcribed by RNA Pol II aid in pulling apart the 2 strands of DNA release of RNA polymerase from promoter into elongation mode1TFIID TBP subunit TATAbinding proteinrecognizes the TATA box contains beta sheet domains in the shape of a saddle that will form hydrogen bonds with the minor groove of DNA causing bending of the double helixhelps expose DNA so that other general transcription factors may bind thought that local distortion of double helix acts as physical landmark to find regions actively transcribed TAF subunit help to recognize sequences other than TATA near TSS 2 TFIIB MAIN ROLEESTABLISHES ORIENTATION recognizes BRE element 35 of TSS single polypeptide anchors RNA polymerase II holoenzyme to the promoter directional binding allows for proper orientation of the transcriptional machinery this allows for only downstream3TFIIF stabilizes RNA polymerase interaction with TBP and TFIIB helps attract TFIIE and TFIIH bound to the RNA polymerase4TFIIE attracts and regulates TFIIH5TFIIH unwinds DNA at the transcription start site phosphorylates Ser5 of the RNA polymerase CTD releases RNA polymerase from the promoter largest and most complex of the factors 89 subunits Helicase activitytransient opening of DNA double helix protein kinase activityphosphorylation of Ser5 in CTD of RNA polymerase II causes conformational change2 Mediator Complex
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