What is the function of DNA ligase?

DNA ligase plays a crucial role in the DNA replication and repair processes by joining DNA strands together. It does this by catalyzing the formation of phosphodiester bonds between the sugar and phosphate backbone of DNA molecules. This function is essential when there are Okazaki fragments during the replication of the lagging strand, as well as during repair processes where breaks in the DNA occur. By sealing these nicks and gaps, DNA ligase ensures the integrity of the genetic material, allowing for stable and functional DNA structures.

In the context of the other choices, modifying RNA strands or degrading DNA sequences does not relate to the primary function of DNA ligase, as these actions are carried out by different enzymes or cellular machinery. Additionally, synthesizing new DNA strands is the primary function of DNA polymerases, not DNA ligase. Thus, the unique ability of DNA ligase to join DNA strands is what defines its critical function in both replication and repair.