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BIOL 205 (111)


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Queen's University
BIOL 205
Ian D Chin- Sang

BIOL205:week 11, lecture 30-31 Transcription → b/c of additional OH: much more susceptible to degradation The four ribonucleotides found in RNA Opposite DNAstrands can serve as template for RNA Overview of transcription Christmas tress =shpwdirection transcription, thousands of Unique polymerases for different types ofRNA polymerases jumping on gene Many RNAs can be simultaneously transcribed from a gene Miller spread: electronic microscopic examination of RNAtranscription if frogs eggs - spread out on grid and examine with electron microscopy RibosomalRNA:upon fertilization zygotic DNA can not launch protein synthesize it needs, mumdeposits ribosomes in egg (utilizing thousands ofRNA genes she made) Promoter sequences in E. coli AlwaysAUG Extra codingat 3' TATAboxat -10 @-35:regionthat is highlyconserved signalthat tells specific proteins to start assemblyon TATAbox - accommodate large RNApolymerase so always starts at TATAbox Transcription initiation in prokaryotes Entire enzyme (allsubunits) Sigma interacts w/ DNA binding unit and catalytic unit to bring it to the right spot Elongation and termination of transcription 80% ofallE. coli DNA containthis hairpinloop Second termination mechanism in prokaryotes - Rho proteinrecognizes rut - creates a stemloop (not GC rich) - causes RNApolymerase to stop - and separates fromDNA - in prokaryotic cells: transcription can occur before translation has even finished - eukaryotic: compartmentalization eukaryotics: all mRNA is made as a precursor (mRNA, tRNA, rRNA) nucleosomes affect replication process: have to be unwind to access DNAfor transcription Eukaryotes have 3 RNA polymerases • RNApolymerase I:localized in the nucleolus ◦ ranscribes ribosomal RNA28S, 18S and 5.8S rRNA– ◦ component of ribosomal subunits • RNApolymerase II: transcribes all mRNA • RNApolymerase III: transcribes tRNA, 5S rRNA - for eachribosome there are hundreds ofproteins that are required whichare made inthe cytoplasm - RNAprocessingmake ribosomalproteins- which needs to go back into te nucleolus to assemble ribosomalRNA - to make a simple ribosome need a coordinationofRNApolymerases Deathcap mushroom: Amanita phalloides alpha – amantin: potent inhibitaor of RNApolymerase II specifically in liver - very painful death RNAPOLYMERASE II TRANSCRIBED GENES → most cellular mRNAs Howeversome can Response elements be w/in introns recognized by various proteins Alittle further out that proks (proks usuallyat ~ -10) Ignored formany years b/c so farupstream/ downstream • control elements : different in almost every gene ◦ each recognized by protein factors known as Transcription factors Overview of transcriptional regulation Compressed in 30nm solenoids:need to unravel to access Able to interact w/ RNA polby folding DNA Modified histone tails protrude from the nucleosome Acetylated histones associated w/ actively transcribed DNA -loosens DNA wrapped around histone NH – terminus (amino-terminal, 2 beginningofprotein) ofeachterminus is “hangingout”inthe nucleoplasm Enhanceosomes recruit chromatin remodelers Transcriptional activator proteins recruit the transcriptional machinery tail ofRNA pol II:unique feature where it leaves offa tail that is going
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