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21 Cards in this Set
- Front
- Back
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Transcription enzyme
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RNA Polymerase
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RNA Polymerase
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a) Processive, ~50 nucleotide/second
b) NO 3' to 5' exonuclease (proofreading) activity |
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Alpha subunit of RNA polymerase.
prokaryotic |
Binds regulatory enzyme
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Beta subunit of RNA polymerase.
prokaryotic |
Phosphodiester bond formation, Grasps DNA
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Beta ' subunit of RNA polymerase.
prokaryotic |
Grasps DNA template
acts with Beta to form "pincers" that grasp DNA template during transcription |
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Sigma subunit of RNA polymerase
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Promoter recognition and initiation.
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Holoenzyme
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alpha+beta+beta'+sigma subunits
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Core Enzyme
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alpha+beta+beta'
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Promoter
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DNA sequence in the template strand of the gene that binds to RNA poly.
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Consensus sequences
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Derived from determining the base found most frequently al each position in the promoter region of the gene.
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Consensus 1
(Pribnow Box) |
TATAAT
(TATA Box) |
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Closed Promoter Complex
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the sigma subunit binds specifically to the promoter sequences to form the closed promoter complex
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Open Promoter Complex
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RNA poly unwinds 17 bps of DNA around the initiation site to form the OPC
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Promoter Specificity
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There are different sigma subunits of RNA poly that bind preferentially to consensus sequences in a given promoter.
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Sigma 70
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Consensus promoter
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Sigma 32
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Heat Shock Promoter
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Sigma 54
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Nitrogen-starvation Promoter
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Elongation
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a) release of sigma subunit upon completion of initiation step
b) elongation by core RNA polymerase. |
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Transcription Bubble
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a) unwound region= 17 bp of DNA
b)RNA/DNA Duplex= 12 bp c)Topoisomerases relieve twisting stress ahead and behind the bubble |
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Termination
(Rho-independent) |
-G-C rich repeat followed by A-T stretch.
-G-C base pairing forms hairpin, which disrupts association with DNA template strand and halts transcription rxn. |
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Termination
(Rho-dependent) |
Binds to specific sequences in RNA and dissociates it from the DNA template
-ATP-dependent helicase activity |
