Explain the mechanism of transcription in a prokaryotic cell.

Explanation

Mechanismof transcription in prokaryotes : Transcription is the process of synthesis of RNA on DNA template. The mechanism of transcription consists of basically three stages: (i) Initiation (ii) Elongation (iii) Termination (i) Initiation : RNA synthesis in prokaryotes is primer independent. In prokaryotes, transcription begins with binding of RNA polymerase to promoter region in DNA. At this stage DNA is double stranded and known as closed complex, later on the DNA unwound and forms open complex. The chain is initiated by addition of ATP or GTP. Initially only upto 9 nucleotides are added to the newly synthesized RNA but the enzyme RNA polymerase is stationary. (ii) Elongation : After initiation RNA polymerase releases its sigma factor and forms ternary elongation complex which consists of RNA polymerase, template DNA and nascent RNA chain. The RNA polymerase synthesizes DNA in 5.-3. direction. The region of unwound DNA which is about 17 bp long is called the “Transcription bubble. and appears to move along the DNA with the polymerase. The polymerase seems to unwind DNA in front of the transcription bubble and rewinds DNA at its rear. (iii) Termination : When polymerase reaches the termination signal it leaves the DNA, the hydrogen bonds of the RNA-DNA helix break, freeing the newly synthesized RNA strand. Termination in prokaryotes is of two types Rho-independent and Rho-dependent termination.