What is the primary function of DNA ligase?

DNA ligase plays a critical role in DNA replication and repair by joining Okazaki fragments on the lagging strand. During DNA replication, the lagging strand is synthesized discontinuously, resulting in short segments known as Okazaki fragments. These fragments need to be connected to create a continuous DNA strand. DNA ligase catalyzes the formation of phosphodiester bonds between the 3’ hydroxyl group of one fragment and the 5’ phosphate group of another, effectively sealing the nicks in the sugar-phosphate backbone of the DNA. This action is essential for maintaining the integrity of the newly synthesized DNA molecule.

In contrast, the other functions listed are performed by different enzymes: unwinding of DNA is accomplished by helicase, RNA nucleotides are synthesized by RNA polymerase during transcription, and stabilization of DNA strands is facilitated by single-strand binding proteins. Therefore, the primary function of DNA ligase specifically relates to the joining of Okazaki fragments, making the response accurate in identifying its role.