lecturenoteschap21-10-4slides

lecturenoteschap21-10-4slides - BCMB 3100 - Chapter 21...

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1 BCMB 3100 - Chapter 21 Transcription & RNA Processing Definition of gene RNA Polymerase Gene coding vs template strand Promoter Transcription in E. coli Transcription factors mRNA processing Biological information flow _______ - a DNA sequence that is transcribed (includes genes that do not encode proteins) ”d ______________________ ” encode proteins or RNA essential for normal activities of the cell (e.g. enzymes in basic metabolic pathways, tRNAs and rRNAs) Four Classes of RNA in living organisms ( review ) Messenger RNA ( mRNA ) - linear “copies” of DNA that encode genetic information. Encode primary structure of protein. ~1-3% of total RNA, relatively unstable (discovered by Jacob & Monod). Non-coding RNA Ribosomal RNA ( rRNA ) - ~80% of total RNA, part of ribosomes (translation machinery) Transfer RNA ( tRNA ) - ~15% of total RNA, 73-95 nucleotides long, carry activated amino acids to ribosomes during translation (Small RNA) - may have catalytic activity and/or associate with proteins to enhance activity, some involved with RNA processing (includes snRNA and microRNA, the latter involved in mRNA degradation, translation inhibition and chromatin remodeling), (long non-coding RNAs (long ncRNAs)): functions being determined.
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2 RNA Synthesis ( E.coli ) Transcription DNA  RNA RNA Polymerase (450 kd) (1960, Hurwitz; Weiss) (recognizes promoter & (binds DNA template) & initiates synthesis) 2   (holoenzyme) forms phosphodiester bond binds rNTPs 2  (core enzyme) (see Table 21.2 & Fig. 21.2) RNA Synthesis 1) Intiation 2) Elongation 3) Termination RNA polymerase is responsible for these function in RNA synthesis E. coli RNA polymerase synthesizes all major types of RNA: mRNA, tRNA, rRNA, small RNA Transcription in E.coli 1) RNA polymerase searches for initiation sites (~2000 in 4,000,000 bp) 2) Unwinds DNA to produce single-stranded template 3) Selects correct ribonucleotide and catalyzes the formation of phosphodiester bonds (totally processive) 4) Detects termination signals 5) Interacts with activators & repressor proteins DNA template RNA polymerase Transcription factors NTPs (ATP,CTP,GTP,UTP) Requirements for Transcription Note: RNA Polymerase does NOT require a primer. RNA chains can be initiated de Mg ++ novo. Mechanism of elongation is the same as for DNA Polymerase: nucleophilic attack by 3’-OH on - phosphate of NTP
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3 Fig 21.3 • RNA polymerase reaction Fig 21.3 (cont) E.coli transcription rate: 30-85 nucleotides/sec Error rate = 10 -6 Error rate 10 RNA Polymerase has no exonuclease activity Fig 21.5 Orientation of a gene Fig 21.6 Promoter sequences for housekeeping genes from 10
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lecturenoteschap21-10-4slides - BCMB 3100 - Chapter 21...

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