Question: 98: Given below are two statements:
Statement I :
DNA polymerases catalyse polymerisation only in one direction, that is 5^{\prime} \rightarrow 3^{\prime}
Statement II :
During replication of DNA, on one strand the replication is continuous while on other strand it is discontinuous.
In the light of the above statements, choose the correct answer from the options given below :
(1) Both Statement I and Statement II are correct
(2) Both Statement I and Statement II are incorrect
(3) Statement I is correct but Statement II is incorrect
(4) Statement I is incorrect but Statement II is correct
Answer: Option (1)
Explanation:
DNA polymerase can add nucleotides only to the free 3^{\prime} hydroxyl group of a growing DNA strand.
Therefore, DNA synthesis always proceeds in the 5^{\prime} \rightarrow 3^{\prime} direction, making Statement I correct.
During DNA replication, the two strands of DNA are antiparallel.
On the template strand running 3^{\prime} \rightarrow 5^{\prime},
replication occurs continuously and forms the leading strand.
On the template strand running 5^{\prime} \rightarrow 3^{\prime},
replication occurs discontinuously in small fragments called Okazaki fragments,
forming the lagging strand.
Thus, Statement II is also correct.
Hence, both Statement I and Statement II are correct.