lec 9 Transcription & RNA processing

lec 9 Transcription & RNA processing - Information...

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Information Flow: base sequence amino acid sequence protein folding nucleus cytoplasm DNA pre-mRNA 5& 5& 3& transcription translation RNA polymerase protein Ribosomal RNA tRNA snoRNA mRNA snRNA microRNA siRNA piRNA RNA folding, base pairing siRNA miRNA piRNA
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How does RNA differ from DNA?
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RNA polymerase Promoter : recruits RNA polymerase Terminator : stops transcription nascent RNA 5& DNA 5& 3& 5& 5& 3& 3& template strand RNA polymerase Transcription ± Requires DNA template but not primer ±5 & 3& synthesis antiparallel to DNA template ± RNA contains uracil instead of thymine mRNA = sense strand ( i.e. , encodes a protein) 3 steps: 1 . Initiation 2. Elongation 3. Termination
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RNA polymerase core Initiation ( E. coli ) TTGACA AACTGT 5& 3& 3& 5& -35 element TATAAT ATATTA - 1 0 element 1 6- 1 9 bp 5-9 bp A/G start site 1 . σ binds σ subunit 5& 5& 3& 3& 2. Open complex 5& 3& 3. Escape from promoter 5& abortive synthesis processive synthesis
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5& 5& 3& 3& 8-9 bp RNA-DNA heteroduplex transcription Elongation ( E. coli ) ± 40 nt per second ± error rate: 1 per 1 00,000 5& unwinding rewinding ~ 1 8 bp unwound DNA 3&
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Termination ( E. coli ) Rho-independent & Inverted repeat followed by run of A±s (template strand) Rho-dependent & Rho binds nascent transcripts, causes termination at 50-90 bp C-rich, G-poor regions. Senses amino acid starvation.
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Transcription and translation are coupled in bacteria
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Eukaryotes have three distinct RNA polymerases Pol I Pol II Pol III miRNA mRNA snRNA snoRNA 5.8S rRNA 1 8S rRNA 28S rRNA tRNAs 5S rRNA α -amanitin insensitive very sensitive to α -amanitin intermediate α -amanitin sensitivity All three RNA polymerases are large, multi-subunit complexes
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lec 9 Transcription & RNA processing - Information...

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