During DNA replication, the term leading strand is applied to the one which replicates in

Options

(a) 5′ → 3′ direction discontinuously
(b) 3′ → 5′ direction continuously
(c) 5′ → 3′ direction continuously
(d) 3′ → 5′ direction discontinuously

Correct Answer:

5′ → 3′ direction continuously

Explanation:

When the double helix of DNA unwinds, DNA replication on one of the two strands (3′ to 5′ strand) can easily proceed continously in 5′ to 3′ direction. This is the leading strand. On the other strand (5′-3′) if the synthesis has to take place in 5′ to 3′ direction, it has to be synthesized in a direction opposite to that on the leading strands. This strand is the lagging strand and on this strand synthesis takes place in segments discontinously and these segments are called Okazagi fragments which then fuse to create an intact lagging strand. This behaviour where the leading strand is synthesized continously and the lagging strand is synthesized discontinously is called semi-discontinous replication.