Explain transcription ?

Explanation

Transcription in Prokaryotes Prokaryotes have only one type,of RNA polymerase for the transcription of all types of genes (structural as well as RNA genes). But different sigma factors may associate with the . same core enzyme at different times for expression of different genes. Transcription occurs in cytoplasm.
I. Initiation
(a) The transcription is initiated by the binding of the holoenzyme to the promoter. The o (sigma) polypeptide of the holoenzyme binds loosely to a sequence of the promoter even before the opening of the DNA double helix. After a complex is formed adjacent sequence of the DNA denatures to form a transcription eye or bubble. The transcription bubble along with the bound holoenzyme is called an open binary complex. (b) Once RNA molecule becomes 8-9 bases long, a factor releases from the RNA polymerase. (c) The p and P. subunits help RNA polymerase in unwinding of DNA molecule. The core enzyme moves along with DNA, binding a nucleoside triphosphate that pair with next DNA base and opening DNA helix as it moves.
II. Elongation Chain elongation proceeds in the direction and the transcription bubble travels with the RNA polymerase. The RNA polymerase after initiation of RNA loses the a factor but continues the polymerisation of ribonucleotides to form RNA. III. Termination When the RNA polymerase reaches the terminator region of DNA, the nascent RNA separates and the RNA polymerase falls off resulting in termination of transcription. RNA polymerase associates transiently with the terminator factor (p) to terminate the transcription. In E. coli, the termination signals fall under two categories-intrinsic or protein factors rho (r) independent.
extrinsic or rho dependent factors. In prokaryotes, the transcribed mRNA is polycistronic.