Why is the lagging strand synthesized in fragments?

Why is the lagging strand synthesized in fragments?

• A. Because the polymerase can only synthesize short fragments at a time.
• B. Because the strand is template for RNA primers.
• C. Because synthesis occurs away from the replication fork in fragments.
• D. Because the lagging strand is not used for coding sequences.

Answer: (C)

Synthesis direction and enzyme chemistry drive why the lagging strand is made in pieces. DNA polymerase can only add nucleotides in the 5′ to 3′ direction and must work off a free 3′ end. As the replication fork opens, the template for the lagging strand runs 3′ to 5′ toward the fork. To keep synthesizing in the required 5′ to 3′ direction, the polymerase must move away from the fork, not toward it. This forces the lagging strand to be built discontinuously as short segments called Okazaki fragments. Each fragment begins with an RNA primer laid down by primase, and later the primers are replaced and the fragments joined by DNA ligase. So the reason the lagging strand is synthesized in fragments is that synthesis must proceed away from the replication fork in the 5′ to 3′ direction, necessitating short, primer-started blocks rather than a single continuous strand. The other options don’t capture this directional and enzymatic constraint.

Synthesis direction and enzyme chemistry drive why the lagging strand is made in pieces. DNA polymerase can only add nucleotides in the 5′ to 3′ direction and must work off a free 3′ end. As the replication fork opens, the template for the lagging strand runs 3′ to 5′ toward the fork. To keep synthesizing in the required 5′ to 3′ direction, the polymerase must move away from the fork, not toward it. This forces the lagging strand to be built discontinuously as short segments called Okazaki fragments. Each fragment begins with an RNA primer laid down by primase, and later the primers are replaced and the fragments joined by DNA ligase.

So the reason the lagging strand is synthesized in fragments is that synthesis must proceed away from the replication fork in the 5′ to 3′ direction, necessitating short, primer-started blocks rather than a single continuous strand. The other options don’t capture this directional and enzymatic constraint.