2. What is TRANSCRIPTION ?
Transcription is the process of copying a
segment of DNA into RNA.
The segments of DNA transcribed into
RNA molecules that can encode proteins
are said to produce messenger RNA
(mRNA).
Transcription in prokaryotes takes place in
cytoplasm.
3. Prokaryotic gene structure
5’ region of promotor sequence Is called
upstream sequence w r.t to coding sequence.
3’ region of termination sequence is called
downstream sequence w.r t codinf sequence.
RNA polymerase binds at promotor sequence.
RNA coding sequence is the portion to be
copied to form RNA
Termination region where transcription stops .
7. 1. Initiation
Sigma factor binds to the promotor
region(-10,-35) sequence.
Core enzyme binds with sigma factor and
promotor sequence but dna is still
closed.This is called closed promotor
complex.
Then holoenzyme unwinds the dna
Strands.Now this unwinded promotor is
called open promotor complex.
8. RNA polymerase gets bind with promotor
at -10 to start transcribing.
Sigma fator is released so that the RNA
polymerase can go forward.
9. 2.Elongation
RNA polymerase moves along transcribing
DNA sequence into single stranded RNA
of coding gene.
When transcribing RNA polymerase
interact with DNA sequence forming
transcription bubble.
DNA helix recoiled as RNA pol moves
forward.
Single RNA strand gets out of the RNA
polymerase .
10. 3.Termination
Rho-independent termination.
Formation of hairpin structure in growing
trascript by complementary base pairing .
Include GC rich inverted repeates to form
U- rich tegion(7-9 nucleotides).
Resulting RNA 3’end lost from active
site,RNA polymerase can’t move forward
and transcription ends.
11. Rho-dependent termination
Termination requires activity of protein
called Rho,whichshow rna-dependent atp
activity.
Rho factor binds to RNA at rut site and
translocates along RNA in 5’ to 3’
direction untill it reaches RNA-DNA hybrid
in RNA polymerase.
There it releasesthe RNA from DNA and
termination stops.
Rut site is rich in C residues and poor in G
residues.
12. Conclusion
Transcription in prokaryotes takes place in cytoplasm.
Transcription is coping gene from dna to rna
Structural gene have promotor ,coding,and termination region.
Transcription have 3 steps—intiation ,elongation and termination stages .