Transcription in Prokaryotes

Molecular biology 🧫- transcription in prokaryotes.
Structural gene,rna polymerase,initiation, elongation, termination.

1. TRANSCRIPTION in PROKARYOTES Molecular biology Presented by JAHNVEE PANDEY

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 .

4. 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.

5. RNA polymerase It is a holoenzyme. Core enzyme + alhpha subunit = RNA polymerase. Core enzyme =2 alpha+beta+beta prime+omega .

6. Transcription process Transcription process includes 3 steps ::

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 .

13. Thank you