Question

a. Identify strands ‘A’ and ‘B’ in the diagram of transcription unit given above and write the basis on which you identified them. 

b. State the functions of Sigma factor and Rho factor in the transcription process in a bacterium. 

c. Write the functions of RNA polymerase-I and RNA polymerase-III in eukaryotes.

Answer 1

a. 

A—Template strand

B—Coding strand

The templates are identified on the basis of polarity with respect to promoter. 

Template strand has polarity 3′ → 5′ and coding strand has polarity 5′ → 3′. 

b. In initiation sigma factor associates with RNA polymerase to initiate transcription and Rho factor gets associated to RNA polymerase to terminate transcription. 

c. RNA polymerase-I transcribes rRNAs. 

RNA polymerase-III transcribes tRNA, 5srRNA and snRNA.