Which enzyme connects two fragments of DNA to make a single fragment?

Which enzyme connects two fragments of DNA to make a single fragment?

• A. Okazaki fragments
• B. Ligase
• C. Topoisomerase
• D. DNA polymerase

Answer: (B)

DNA ligase is the enzyme that connects two DNA fragments into a single continuous strand. After replication on the lagging strand, short segments called Okazaki fragments are synthesized and later need to be joined. The ligase seals the nicks between these fragments by forming phosphodiester bonds, using energy from ATP (in eukaryotes) or NAD+ (in bacteria). This creates a continuous backbone. Other enzymes have different roles: DNA polymerase builds new DNA but doesn’t join fragments, and topoisomerase relieves supercoiling rather than linking fragments.

DNA ligase is the enzyme that connects two DNA fragments into a single continuous strand. After replication on the lagging strand, short segments called Okazaki fragments are synthesized and later need to be joined. The ligase seals the nicks between these fragments by forming phosphodiester bonds, using energy from ATP (in eukaryotes) or NAD+ (in bacteria). This creates a continuous backbone. Other enzymes have different roles: DNA polymerase builds new DNA but doesn’t join fragments, and topoisomerase relieves supercoiling rather than linking fragments.