What does DNA ligase do in DNA replication?

DNA ligase plays a crucial role in DNA replication by facilitating the joining of Okazaki fragments. During the replication of the lagging strand, DNA polymerase synthesizes short segments of DNA, known as Okazaki fragments, in the opposite direction to the movement of the replication fork due to the antiparallel nature of DNA strands. These fragments are synthesized separately and are initially not connected.

DNA ligase specifically targets the nicks, which are short gaps in the phosphate backbone between these Okazaki fragments, and catalyzes the formation of phosphodiester bonds to seal these nicks. This action is essential for creating a continuous DNA strand and ensuring the integrity of the genetic material during cell division.

The other aspects of DNA replication, such as adding nucleotides to the leading strand, unwinding the DNA double helix, or forming RNA primers, are performed by other enzymes, such as DNA polymerase, helicase, and primase, respectively. Therefore, the primary function of DNA ligase is integral to the final steps of lagging strand synthesis.