During replication, which enzyme seals Okazaki fragments by joining them to form a continuous strand?

During replication, which enzyme seals Okazaki fragments by joining them to form a continuous strand?

• A. RNA primase
• B. DNA polymerase
• C. DNA ligase
• D. Helicase

Answer: (C)

During DNA replication on the lagging strand, synthesis occurs in short segments called Okazaki fragments that must be stitched together into one continuous strand. After each fragment is extended and primers are removed, the final joining step is done by DNA ligase. This enzyme forms a phosphodiester bond between the adjacent fragments’ sugar-phosphate backbones, effectively sealing the nicks and completing the strand. It uses energy from ATP (or a related molecule, depending on the organism) to make that bond. Other enzymes have different roles: helicase unwinds the double helix, RNA primase lays down the RNA primer to start a fragment, and DNA polymerase adds nucleotides to build the new DNA strand (and can replace primers) but it cannot seal the backbone between fragments. Hence, DNA ligase is the one that completes the connection between Okazaki fragments.

During DNA replication on the lagging strand, synthesis occurs in short segments called Okazaki fragments that must be stitched together into one continuous strand. After each fragment is extended and primers are removed, the final joining step is done by DNA ligase. This enzyme forms a phosphodiester bond between the adjacent fragments’ sugar-phosphate backbones, effectively sealing the nicks and completing the strand. It uses energy from ATP (or a related molecule, depending on the organism) to make that bond. Other enzymes have different roles: helicase unwinds the double helix, RNA primase lays down the RNA primer to start a fragment, and DNA polymerase adds nucleotides to build the new DNA strand (and can replace primers) but it cannot seal the backbone between fragments. Hence, DNA ligase is the one that completes the connection between Okazaki fragments.