EXPLAIN the process of transcription in bacteria with diagram.
The process of synthesising proteins from the DNA template is known as protein synthesis; where, the process of conversion of DNA into RNA is known as transcription and the process of conversion of RNA into polypeptide chain is known as translation.
Transcriptional Unit- A transcriptional unit has primarily three regions:
Promoter – Marks the beginning of transcription; RNA polymerase binds here
Structural gene – Part of the DNA that is actually transcribed
Terminator – Marks the end of transcription
Transcription has three steps – initiation, elongation, and termination.
Initiation:RNA polymerase is an enzyme that catalyses in only one direction i.e., 5' to 3' and so uses the strand with polarity 3'→ 5' as a template or template Strand. It binds with the promoter to initiate the process of transcription.Association with initiation factors ( sigma factor)alters the specificity of RNA polymerase to initiate the transcription.
Elongation:RNA polymerase uses nucleotide triphosphate as substrate, and polymerisation occurs according to complementarity.
Termination:Termination occurs when termination factor (P) alters the specificity of RNA polymerase to terminate the transcription. Rho factor is responsible for the termination of mRNA chain in E.coli. If it is not expressed, then the chain will fail to terminate at the right length.
As the RNA polymerase proceeds to perform elongation, a short stretch of RNA remains bound to the enzyme. As the enzyme reaches the termination region, this nascent RNA falls off and transcription is terminated.
Here is given diagram for transcription.
Transcription consist of 3 steps:->
1) Initiation:-RNA polymerase along with the sigma factor (initation factor) bind with the promotor & start transcription. DNA duplex are opned by unbindase and single stranded binding protein. RNA polymerase bring ribonucleotides complementary to nucleotide present in the templete strand and start the RNA synthesis.
2) Elongation:-with the help of RNA polymerase the adjusent nucleotiodes held over DNA Template join to form RNA chain. As the RNA formation start sigma factor seperate. RNA polymerase (co-enzyme) move along DNA template causing elongation of RNA change at the rate of 30 nucleotides per second.
3)Termination:- At the 3' end their is present rho factor (terminator factor) bind with RNA polymerase and its activity causing stopage of RNA synthesis rho factor has ATPase activity helps in release of complete RNA chain. A released RNA is now called Primary Transcript or hnRNA(heterogeneous nuclear RNA) which undergo process to form functional RNA.
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