What are Okazaki fragments?

• A. Short DNA segments synthesized on the lagging strand that are later joined by ligase.
• B. Short RNA primers used by primase.
• C. Long continuous segments on the leading strand.
• D. Fragments of RNA that are removed by DNA polymerase I.

Answer: (A)

During DNA replication, the lagging strand is synthesized in short segments known as Okazaki fragments. Because this strand runs opposite the direction of fork movement, DNA polymerase can only build in the 5' to 3' direction in small bursts, creating these fragments. Each fragment begins with an RNA primer laid down by primase, but the fragment itself is DNA. After synthesis, the RNA primers are removed and replaced with DNA, and the fragments are joined by DNA ligase to form a continuous strand. The leading strand, by contrast, is synthesized continuously toward the fork.