Which strand is synthesized in fragments known as Okazaki fragments?

• A. Leading strand
• B. Lagging strand
• C. Double helix
• D. Base pairs

Answer: (B)

DNA replication can only build DNA in the 5' to 3' direction, and the two template strands run antiparallel to each other. On the strand that runs 3' to 5' toward the fork, synthesis can proceed continuously in the direction of fork movement, creating the leading strand. The opposite template runs 5' to 3' away from the fork, so the polymerase must work in short bursts as the fork opens new sections of template. These short bursts form Okazaki fragments, each starting with an RNA primer laid down by primase and then extended by DNA polymerase before the gaps are joined by DNA ligase. So, the strand that is synthesized in fragments is the lagging strand.

The other options don’t describe a strand synthesized in fragments: the leading strand is the continuously synthesized partner, while the double helix refers to DNA’s overall structure, and base pairs are the paired nucleotides rather than a strand being synthesized.