Transcription
- Transcription RNA process by which is the from the synthesized template, forming
first DNA step of gene expression.
- It is a tightly regulated, enzyme driven process occuring three major stages
A) Initiation
B) Elongation
c) Termination
A) Initiation
INITIATION is the first and most regulator stage of where RNA polymerase identifies the
starting point of a gene, binds to it and begins RNA synthesis.
This step determines. which gene is strongly expressed, when, and how strongly
RNA Polymerase Holoenzyme: The Key Enzyme.
In prokaryotes (eg: E.coli) transcription is carried out by a single RNA polymerase.
Structure
Core Enzyme (a₂ββ’ω)
-catalyzes RINA synthesis cannot recognize promoter but
Holoenzyme :- Core + sigma factor - Capable of promoter recognition and initiation.
Structure and Functions:-
Alpha(2units) protein -Enzyme assembly + promoter recognition.
Beta protein -RNA chain intiation & polymerization.
Betadash protein- Binds to DINA template
Omega protein -Enzyme stability & folding-
Sigma protein-Recognize promoter and initates transcription.
, Role of Sigma factor:
Function
- Acts like guide or GPS for RNA polymerase.
-Helps the enzyme locate and bind to specific promoter regions on the DNA.
-sigma 70 is the primary sigma Factor in E-coli normal conditions.
Without sigma , the core enzyme binds DNA randomly and cannot intiate transcription
3) Prompter :The start Point of Transcription:-
A promoter specific DNA sequence is upstream of gene that acts as a binding site for RNA
polymerase.
−35 region: Consensus sequence → TTGACA
−10 region (Pribnow box): Consensus → TATAAT
Located ~10 bases upstream from the transcription start site (+1).
These sequences are recognized by the σ factor of RNA polymerase.
Step-by-Step Mechanism of Initiation
Step 1: Formation of Holoenzyme
The RNA polymerase core enzyme binds with σ factor, forming the holoenzyme
Now, it is competent to locate promoters.
Step 2: Promoter Recognition and Binding
The holoenzyme scans DNA for promoter sequences.
It binds to the −35 region, forming the closed complex (DNA still double-stranded).
Step 3: Open Complex Formation
- Transcription RNA process by which is the from the synthesized template, forming
first DNA step of gene expression.
- It is a tightly regulated, enzyme driven process occuring three major stages
A) Initiation
B) Elongation
c) Termination
A) Initiation
INITIATION is the first and most regulator stage of where RNA polymerase identifies the
starting point of a gene, binds to it and begins RNA synthesis.
This step determines. which gene is strongly expressed, when, and how strongly
RNA Polymerase Holoenzyme: The Key Enzyme.
In prokaryotes (eg: E.coli) transcription is carried out by a single RNA polymerase.
Structure
Core Enzyme (a₂ββ’ω)
-catalyzes RINA synthesis cannot recognize promoter but
Holoenzyme :- Core + sigma factor - Capable of promoter recognition and initiation.
Structure and Functions:-
Alpha(2units) protein -Enzyme assembly + promoter recognition.
Beta protein -RNA chain intiation & polymerization.
Betadash protein- Binds to DINA template
Omega protein -Enzyme stability & folding-
Sigma protein-Recognize promoter and initates transcription.
, Role of Sigma factor:
Function
- Acts like guide or GPS for RNA polymerase.
-Helps the enzyme locate and bind to specific promoter regions on the DNA.
-sigma 70 is the primary sigma Factor in E-coli normal conditions.
Without sigma , the core enzyme binds DNA randomly and cannot intiate transcription
3) Prompter :The start Point of Transcription:-
A promoter specific DNA sequence is upstream of gene that acts as a binding site for RNA
polymerase.
−35 region: Consensus sequence → TTGACA
−10 region (Pribnow box): Consensus → TATAAT
Located ~10 bases upstream from the transcription start site (+1).
These sequences are recognized by the σ factor of RNA polymerase.
Step-by-Step Mechanism of Initiation
Step 1: Formation of Holoenzyme
The RNA polymerase core enzyme binds with σ factor, forming the holoenzyme
Now, it is competent to locate promoters.
Step 2: Promoter Recognition and Binding
The holoenzyme scans DNA for promoter sequences.
It binds to the −35 region, forming the closed complex (DNA still double-stranded).
Step 3: Open Complex Formation
