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Uploaded byJahnveePandey
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Transcription in Prokaryotes

Transcription in prokaryotes is the process of copying DNA into RNA, occurring in the cytoplasm, and involves three main steps: initiation, elongation, and termination. The RNA polymerase enzyme, which includes a sigma factor, binds to the promoter sequence to begin transcription, producing messenger RNA (mRNA) that encodes proteins. Termination can occur via rho-independent and rho-dependent mechanisms, concluding the transcription process.

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Molecular Biology•
TRANSCRIPTION in PROKARYOTES MOLECULAR BIOLOGY Presented by JAHNVEE PANDEY
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.
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 .
Promotor sequence  Promotor sequence (E.coli)::  5’-TTGACA-3’ (pribnow box) @ -10 sequence.  5’-TATAAT-3’ (tata box) @ -35 sequence.  Signa factor binds to promotor sequence.
RNA polymerase  It is a holoenzyme.  Core enzyme + alhpha subunit = RNA polymerase.  Core enzyme =2 alpha+beta+beta prime+omega .
Transcription process  Transcription process includes 3 steps ::
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.
 RNA polymerase gets bind with promotor at -10 to start transcribing.  Sigma fator is released so that the RNA polymerase can go forward.
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 .
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.
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.
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 .
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