Arrange the following events of transcription in bacteria in the correct sequence:
A. RNA polymerase reaches the terminator region.
B. RNA polymerase associates transiently with the initiation-factor (σ) and binds to the promoter.
C. RNA polymerase uses nucleoside triphosphates as substrate and polymerises in a template-dependent fashion.
D. With the termination-factor (ρ), the nascent RNA falls off, and so does the RNA polymerase.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B, C, A, D
In bacteria a single RNA polymerase copies the DNA into RNA in three steps: initiation, elongation and termination. The enzyme can carry out only elongation by itself. It needs the σ factor to start and the ρ factor to stop.
B comes first. RNA polymerase joins the initiation-factor (σ) and binds to the promoter. This is initiation.
C comes second. The enzyme uses nucleoside triphosphates as substrate and builds the RNA on the template strand, following base pairing. This is elongation.
A comes third. Elongation goes on until the polymerase reaches the terminator region at the end of the gene.
D comes last. With the termination-factor (ρ), the new RNA falls off and so does the RNA polymerase. This is termination.
NCERT Extract:
Types of RNA and the Process of Transcription – “… 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 elongation. 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 (σ) and termination-factor (ρ) to initiate and terminate the transcription, respectively.”