BIO206H5 Lecture Notes - Lecture 8: Sigma Factor, Globular Protein, Ribonucleotide

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1 Dec 2013
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binding of RNA polymerase to a promoter sequence
Initiation
sequential addition of ribonucleotides as prescribed by the DNA template strand
Elongation
dissociation of RNA polymerase
release of primary transcript from template
Termination
3 Stages of Transcription
Control of transcription is VERY IMPORTANT!
Maintain protein degradation at a constant value - Increasing/ decreasing rate of synthesis of
mRNA
Regulation
*Prokaryotes: Signals in DNA tell RNA polymerase where to start and finish
First assessment of where promoter might be upstream
Success for RNA polymerase need to be able to transcribe the whole DNA strand
Promoter - indicate starting point for RNA synthesis
-
Terminator - indicate stop site
-
Recognizes different promoters
Released when transcription has begun (after formation of 10-13 nucleotides)
Reunites with RNA polymerase after transcription
Sigma factor - subunit in RNA polymerase that recognizes the promoter on DNA
-
RNA polymerase: The key enzyme of RNA synthesis
Bacterial RNA polymerase is a globular protein complex
A core enzyme containing 5 subunits with the catalytic site
Composed of:
Lecture 8/ Chapter 7
October-12-13
6:34 PM
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A core enzyme containing 5 subunits with the catalytic site
A variable regulatory factor: sigma [σ]
RNA polymerase holoenzyme = Core + σ
Bacterial RNA Polymerase
One very large enzyme complex!
Prokaryotes: only one type;
α-subunit x2
36,000 Da x 2
β-subunit
150,600 Da
β’-subunit
155,600 Da
ω-subunit
10,000 Da
-------------------
422,200 Da
Dimensions: 10 x 10 x 15 nm
Core Enzyme Quaternary Structure:
Variable Component: Sigma Factor (δ): between 7 and 60 different types e.g. δ70, δ32
Variation in sigma factor allows RNA polymerase to recognize different genes to be activated
αα
recognizes the upstream element (-40 to -70) in DNA. This is in addition to the σ factor
recognizing the -10 to -35 region.
β
has the polymerase activity (catalyzes the synthesis of RNA) which includes chain initiation
and elongation.
β’
binds to DNA - allows holoenzyme to remain situated
ω
polymerase stability, chaperone
σ
proteins that recognize & bind to specific promoter regions of a gene. Recruits RNA
polymerase core complex forming the holoenzyme. (sigma factor)
During elongation phase, sigma factor is no longer attached
Bending process allow DNA to unwound and separate its two strands
Separation of strands at L shaped DNA
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Separation of strands at L shaped DNA
Initiation
Closed complex to open complex separation allows initial insertion of ribonucleotide
Sigma Factor finds & binds Promoter
RNA polymerase: promoter binding site
RNA Polymerase: extended promoter binding site
Sigma 70
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Document Summary

Initiation binding of rna polymerase to a promoter sequence. Elongation sequential addition of ribonucleotides as prescribed by the dna template strand. Termination dissociation of rna polymerase release of primary transcript from template. Maintain protein degradation at a constant value - increasing/ decreasing rate of synthesis of mrna. *prokaryotes: signals in dna tell rna polymerase where to start and finish. First assessment of where promoter might be upstream. Success for rna polymerase need to be able to transcribe the whole dna strand. Promoter - indicate starting point for rna synthesis. Sigma factor - subunit in rna polymerase that recognizes the promoter on dna. Released when transcription has begun (after formation of 10-13 nucleotides) Rna polymerase: the key enzyme of rna synthesis. Bacterial rna polymerase is a globular protein complex. A core enzyme containing 5 subunits with the catalytic site. Variation in sigma factor allows rna polymerase to recognize different genes to be activated.

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