What does DNA ligase do in cloning?

What does DNA ligase do in cloning?

• A. Seals nicks in the sugar-phosphate backbone to join fragments
• B. Cuts DNA at specific sequences
• C. Unwinds DNA strands
• D. Synthesizes RNA primers

Answer: (A)

In cloning, the main job of DNA ligase is to seal nicks in the sugar-phosphate backbone so that DNA fragments are joined into one continuous molecule. After you cut the vector and the insert, there are exposed ends that need to be stitched together; ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, effectively linking the fragments into a single, ligated DNA molecule that can be replicated in a host. This sealing step is essential—without it, the fragments would remain separate and the recombinant DNA couldn’t function properly. Other activities mentioned belong to different enzymes: cutting DNA at specific sequences is done by restriction enzymes, unwinding DNA strands is done by helicase, and synthesizing RNA primers is done by primase or RNA polymerase, not DNA ligase.

In cloning, the main job of DNA ligase is to seal nicks in the sugar-phosphate backbone so that DNA fragments are joined into one continuous molecule. After you cut the vector and the insert, there are exposed ends that need to be stitched together; ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, effectively linking the fragments into a single, ligated DNA molecule that can be replicated in a host. This sealing step is essential—without it, the fragments would remain separate and the recombinant DNA couldn’t function properly. Other activities mentioned belong to different enzymes: cutting DNA at specific sequences is done by restriction enzymes, unwinding DNA strands is done by helicase, and synthesizing RNA primers is done by primase or RNA polymerase, not DNA ligase.