Question

What is the direction in which the transcript produced by RNA polymerase grows?

(a) 3’->5’ direction on 3’->5’ strand

(b) 5’->3’ direction on 5’->3’ strand

(c) 3’->5’ direction on 5’->3’ strand

(d) 5’->3’ direction on 3’->5’ strand

I got this question in an interview for job.

My question comes from Transcription in Prokaryotes : Initiation in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Correct option is (d) 5’->3’ direction on 3’->5’ strand

Easy explanation: In the process of RNA synthesis there is a short phase of hybrid DNA-RNA formation. This is possible only when two strands are oppositely oriented. As 3’-OH is necessary for adding new nucleotides, RNA is synthesized from 5’->3’ direction, so the template must be 3’->5’ oriented.