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Ch11transcription

Ch11transcription - Transcrip)on ,catalyzedby...

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Transcrip)on • RNA synthesized on a DNA template, catalyzed by DNA‐dependent RNA polymerase • ATP, GTP, CTP, and UTP are required, as is Mg 2+ • no RNA primer is required • the RNA chain is synthesized in the 5’ ‐> 3’ direc)on; the nucleo)de at the 5’ end of the chain retains its triphosphate (ppp) group • the DNA base sequence contains signals for ini)a)on and termina)on of RNA synthesis; the enzyme binds to and moves along the DNA template in the 3’ ‐> 5’ direc)on • the DNA template is unchanged
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Transcrip)on in prokaryotes
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The Basics of Transcrip)on
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Promoter sequence Simplest of organisms contain a lot of DNA that is not transcribed RNA polymerase needs to know which strand is template strand, which part to transcribe, and where first nucleo)de of gene to be transcribed is Promoters ‐DNA sequence that provide direc)on for RNA polymerase
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First phase of transcrip)on is ini)a)on Ini)a)on begins when RNA polymerase binds to promoter and forms closed complex AVer this, DNA unwinds at promoter to form open complex , which is required for chain ini)a)on
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AVer strands separated, transcrip)on bubble of ~17 bp moves down the DNA sequence to be transcribed RNA polymerase catalyzes forma)on of phosphodiester bonds between the incorp. ribonucleo)des Topoisomerases relax supercoils in front of and behind transcrip)on bubble
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• Two types of termina)on mechanisms: • intrinsic termina)on‐ controlled by specific sequences, termina2on sites • Termina)on sites characterized by two inverted repeats
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