In DNA replication, which strand is synthesized discontinuously in short segments?

In DNA replication, which strand is synthesized discontinuously in short segments?

• A. Leading
• B. Okazaki
• C. Template
• D. Lagging

Answer: (D)

The essential idea is that DNA polymerase can only synthesize DNA in the 5' to 3' direction. At the replication fork, one template runs 3' to 5' toward the fork, allowing continuous synthesis toward the fork—the leading strand. The opposite template runs 5' to 3' toward the fork, so synthesis must occur in short, separate pieces that are later joined. These short pieces are called Okazaki fragments, and their synthesis on this template is what makes the lagging strand discontinuous. In contrast, the leading strand is synthesized continuously.

The essential idea is that DNA polymerase can only synthesize DNA in the 5' to 3' direction. At the replication fork, one template runs 3' to 5' toward the fork, allowing continuous synthesis toward the fork—the leading strand. The opposite template runs 5' to 3' toward the fork, so synthesis must occur in short, separate pieces that are later joined. These short pieces are called Okazaki fragments, and their synthesis on this template is what makes the lagging strand discontinuous. In contrast, the leading strand is synthesized continuously.