Question

The cell must remove and replace an RNA primer with DNA, if DNA pol I was the only enzyme available to do this, which activities must it use?

a. 3'-5' exonuclease and 5'-3' polymerase

b. 5'-3' exonuclease and 5'-3' polymerase

c. 5'-3' exonuclease and 3'-5' polymerase

d. 3'-5' exonuclease and 3'-5' polymerase

Answer 1

Ans) The correct option is "b" . DNA polymerase-I has small fragment with 5' - 3' exonuclease activity and large fragment (Klenow fragment) with 3'-5' exonuclease activity. For the removal of primer, 5' - 3' exonuclease activity is required. Once,the RNA primer is removed, DNA is synthesized from 5' - 3' end by DNA Pol-I since the DNA synthesis occurs from the extension of RNA primer from 5' end.