Question

The enzyme which has polymerizing activity in 5’→3’ direction but exonuclease activity in 3’→ 5’ direction only is
A. RNA polymerase III
B. DNA polymerase II
C. DNA polymerase I
D. All of these

Answer 1

Hint: Polymerase is among the enzymes being used to synthesize nucleic acids. DNA polymerase is an enzyme that always synthesizes DNA whereas RNA polymerase is such an enzyme that synthesizes RNA. Exonucleases seem to be enzymes that really work by cleaving nucleotides one at a time from the end (exo) of the polynucleotide chain.

Complete answer: DNA polymerase I catalyze the polymerization directed by the template of nucleotides into double-stranded DNA in a 5'-3' direction. DNA Polymerase I exhibits a 3’ – 5’ exonuclease function or a "proofreading", that lessens the failure rate during replication of DNA, and then also comprises an exonuclease action of 5' - 3, which empowers the enzyme to substitute nucleic acids in the rising DNA strand by nick-translation. Pol I might add nucleotides to the 3′-OH group on a single-strand double helix. Such an event benefits from the ability of pol I both to detect the 3′-OH group anywhere else in the helix as well as to shift the base-paired strand forward of the free 3′-OH group. This activity is considered strand displacement
So, the correct answer is option (C).

Note: DNA polymerase is also known as Pol I. In E. coli and several other bacteria, the gene which represents Pol I is defined as polA. The biological role of Pol I is predominantly to fix any damage to DNA, and it also helps to link Okazaki fragments by eliminating RNA primers and replacing DNA strands.