Lecture 5 RNA Synthesis and Processing

Lecture 5 RNA Synthesis and Processing - Chapter29...

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Chapter 29 RNA Synthesis and Processing  
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RNA structure and synthesis RNA carries information for protein synthesis and is synthesized in a sequence  specific manner from DNA Protein synthesis Genetic information
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RNA transcription RNA polymerase      (RNA) n   residues  + ribonucleoside triphosphate   (RNA) n +1  residues  + PP i Reaction direction complementary not required antisense strand same sequence to the sense strand (T replaced by U) 5’ 3’
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RNA synthesis:  Initiation ~ Elongation ~ Termination RNA polymerase   – enzyme that catalyzes the formation of an RNA strand  complementary to a DNA template. Mg 2+ Active site:
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Prokaryotic RNA transcription Two functional states of RNA polymerase holoenzyme   α 2 ββ σ σ    initiation core enzyme  α 2 ’   elongation, termination ββ →
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1. Initiation a) Search for initiation site (promoter ) ~2000 promoters in  E. coli  genome    subunit σ    specific initiation: reads sequence in DNA                       (walk) to find specific promoter sequences “Consensus  (average)sequence” Actual sequence and  distance regulate the  transcription efficiency sequence sequence
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b) Unwinding of DNA double helix Unwinds ~17 bp of DNA (1.6 turns of helix) Negative supercoiling may promote DNA unwinding (decrease Lk) Closed promoter complex (double helical)                                     Open promoter complex (unwound) c) Base pairing of 1 st  nucleotide pppG or pppA (GTP or ATP)
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2. Elongation 5’   3’ direction Holoenzyme   core enzyme (  released σ ; binds more strongly to DNA) “Transcription bubble ”: the region containing DNA, RNA, RNA polymerase Rate of elongation: ~  50 nucleotides/sec RNA polymerase lacks any exonuclease activity (no repair function) Fidelity of transcription ~ 1 error / 10 4~5  bases                     replication ~ 1 error / 10 10  bases                                         [DNA: transmitted to progeny = needs higher fidelity] Transcription bubble (~8 bp) DNA-RNA separation
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3. Termination Formation of phosphodiester bonds stops RNA-DNA hybrid dissociates DNA-DNA hybrid reforms
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This note was uploaded on 01/16/2012 for the course BIOLCHEM 415 taught by Professor Michaeluhler during the Fall '06 term at University of Michigan.

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Lecture 5 RNA Synthesis and Processing - Chapter29...

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