What characterizes the synthesis of the lagging strand during DNA replication?

• A. Continuous synthesis toward the fork.
• B. Requires RNA primers to begin each fragment but is synthesized in one long piece.
• C. Synthesized in short segments away from the fork called Okazaki fragments.
• D. Incorporates RNA nucleotides into DNA.

Answer: (C)

DNA polymerases can only add nucleotides in the 5' to 3' direction, and the two strands at the replication fork run antiparallel. The leading strand can be made continuously toward the fork, but the lagging strand, which runs in the opposite orientation, must be copied in short, discontinuous pieces. These pieces are produced in the 5' to 3' direction away from the fork and are called Okazaki fragments. Each fragment begins with an RNA primer laid down by primase, and after the fragments are synthesized, the RNA primers are removed and replaced with DNA, and the fragments are sealed together by ligase. That’s why this description—short segments away from the fork known as Okazaki fragments—best characterizes lagging-strand synthesis. The other options describe leading-strand synthesis, continuous synthesis, or RNA incorporated into a DNA strand, which is not the standard representation of lagging-strand synthesis.