What is the purpose of DNA ligase in genetic engineering?

• A. It recognizes specific DNA sequences for editing
• B. It joins DNA fragments together by forming phosphodiester bonds
• C. It unwinds DNA for replication
• D. It catalyzes the transcription of DNA to RNA

Answer: (B)

The purpose of DNA ligase in genetic engineering is to join DNA fragments together by forming phosphodiester bonds. This enzyme plays a crucial role in the process of DNA replication and molecular cloning, where it facilitates the linking of DNA strands. When DNA is cut by restriction enzymes, for example, it creates fragments with free ends that need to be joined to create recombinant DNA molecules. DNA ligase catalyzes the formation of covalent bonds between the phosphate group on one DNA fragment and the hydroxyl group on another, effectively sealing nicks and creating a continuous strand of DNA.

Understanding this function is essential in genetic engineering, as it allows for the successful assembly of genes into plasmids or other vectors that can be introduced into host cells. Additionally, it is also key in processes like cloning, where different segments of DNA need to be combined to produce specific proteins or genetically modified organisms. The other options describe different functions or roles that do not relate to the primary activity of DNA ligase.