What does DNA ligase do in replication?

Correct answer: It joins Okazaki fragments

The governing concept is discontinuous synthesis of the lagging DNA strand. DNA polymerase can extend a new strand only in the 5′→3′ direction, so the lagging strand is produced as short Okazaki fragments. After RNA primers are removed and the gaps are filled with DNA, a remaining nick exists between adjacent fragments. DNA ligase seals this nick by forming a phosphodiester bond between a 3′-hydroxyl group and a 5′-phosphate group. Therefore option A is correct. Helicase unzips DNA, primase makes RNA primers, and DNA polymerase selects and adds complementary nucleotides.