Explain different types of $RNA$ and Explain the process of transcription.

Three major types of $RNAs$ found in bacteria are :

$(i)$ $mRNA$ : [messenger $RNA$]which provides the template for translation.

$(ii)$ $tRNA$ : (transfer $RNA$) which brings amino acid and reads the genetic code.

$(iii)$ $rRNA$ : (ribosomal $RNA$) which plays structural and catalytic role during translation.

All three $RNAs$ are needed for synthesis of a protein in a cell.

There is single $DNA$ dependent $RNA$ polymerase that catalyses transcription of all types of $RNA$ in bacteria.

$RNA$ polymerase binds to promoter and initiates transcription (initiation).

It uses nucleoside triphosphates as substrate and polymerises in a template depended fashion following the rule of complementarity.

It somehow also facilitates opening of the helix and continues alongation.

Only a short stretch of $RNA$ remains bound to the enzyme.

Once the polymerases reaches the terminator region the nascent $RNA$ falls off, so also the $RNA$ polymerase.

This results in termination of transcription.

The $RNA$ polymerase is only capable of catalysing the process of elongation.

It associates transiently with initiation factor $(\sigma)$ and termination factor $(\rho$ ) to initiate and terminate the transcription, respectively.

Association with these factor alter the specificity of the $RNA$ polymerase to either initiate or terminate.