Question

Question: Explain why the activesite of poly(A) polymerase is much narrower than that of DNA and RNA polymerases.

Short answer

The narrow size of the active site of poly(A) polymerase is due to the fact that it does not need any template for its activity unlike the DNA and RNA polymerases which need to match their sequences with the template which is needed for its activity.

Step-by-step solution

Size of the active site

Enzymes which require template for their activity must have bigger size of the active site. Smaller or narrower size of the active site occurs if template is not needed for its activity.

Explanation

Polymerase A does not require a template for its activity and thus the active site of poly(A) polymerase whereas DNA and RNA polymerases require a template and thus have a bigger sized active site which can match with the sequence on the template which is needed for its activity.