What is the role of DNA ligase in DNA replication?

DNA ligase plays a crucial role in DNA replication, particularly during the synthesis of the lagging strand. The lagging strand is synthesized in short segments known as Okazaki fragments, which are produced because DNA is synthesized in a 5' to 3' direction. After these fragments are formed, DNA ligase is responsible for joining them together to create a continuous strand of DNA.

This joining process involves sealing the nicks that occur between the Okazaki fragments, forming phosphodiester bonds to link the sugar-phosphate backbones of the DNA. Without the action of DNA ligase, the lagging strand would remain fragmented, making it impossible for the replication process to produce a complete and functional DNA molecule.

In contrast, the other options refer to different roles that are filled by other enzymes or proteins during DNA replication. For example, RNA primers are added by primase, single-strand binding proteins stabilize unwound strands, and helicase is the enzyme that unwinds the DNA helix. Each of these functions is essential, but they do not involve the joining of DNA fragments, which is specifically the role of DNA ligase.