Which enzyme connects fragments of DNA together in replication?

• A. Helicase
• B. DNA Polymerases
• C. Ligase
• D. Topoisomerase

Answer: (C)

Joining fragments created on the lagging strand is essential for a continuous DNA molecule. During replication, the lagging strand is synthesized in short segments called Okazaki fragments. DNA polymerase can add nucleotides to extend these fragments, but it cannot seal the gaps between them. DNA ligase steps in to form the final phosphodiester bonds that link adjacent fragments, effectively sealing the sugar–phosphate backbone. This enzyme typically uses energy to make those bonds, completing the replication process on that strand. The other enzymes have different roles: helicase unwinds the double helix, topoisomerase relieves torsional stress, and polymerases build new DNA but do not join fragments.