Okazaki fragments are best described as what?

• A. Okazaki fragments are short segments synthesized on the lagging strand in the 5' to 3' direction away from the replication fork.
• B. Okazaki fragments are long continuous segments on the leading strand.
• C. Okazaki fragments are RNA primers produced by primase.
• D. Okazaki fragments are segments of DNA formed only in prokaryotes.

Answer: (A)

Discontinuous synthesis on the lagging strand requires short DNA segments that are synthesized in the 5' to 3' direction away from the replication fork. On the lagging strand, DNA polymerase can only add nucleotides in the 5' to 3' direction, so as the fork opens, synthesis occurs in short bursts that move away from the fork, forming Okazaki fragments. Each fragment starts with an RNA primer laid down by primase, then DNA polymerase extends the fragment until it encounters the previous one, and later the primers are removed and the fragments joined by DNA ligase. The other statements don’t fit: the leading strand is synthesized continuously toward the fork; the fragments are DNA segments, not the RNA primers themselves; and Okazaki fragments occur in both prokaryotes and eukaryotes, not only in prokaryotes.