Which enzyme seals phosphodiester bonds between Okazaki fragments?

Which enzyme seals phosphodiester bonds between Okazaki fragments?

• A. Primase
• B. Ligase
• C. Polymerase
• D. Helicase

Answer: (B)

Joining Okazaki fragments requires a ligase enzyme. On the lagging strand, DNA is built in short pieces called Okazaki fragments. After each fragment is extended and primers are removed, there’s a missing phosphodiester bond between the 3′ end of one fragment and the 5′ end of the next. DNA ligase seals this nick by forming a new phosphodiester bond, tying the fragments together and producing a continuous strand. This step uses energy (from ATP in eukaryotes or NAD+ in prokaryotes). The other enzymes have different roles: primase lays down RNA primers, polymerase fills in DNA and replaces primers, and helicase unwinds the double helix. Sealing the backbone between fragments is the job that ligase performs.

Joining Okazaki fragments requires a ligase enzyme. On the lagging strand, DNA is built in short pieces called Okazaki fragments. After each fragment is extended and primers are removed, there’s a missing phosphodiester bond between the 3′ end of one fragment and the 5′ end of the next. DNA ligase seals this nick by forming a new phosphodiester bond, tying the fragments together and producing a continuous strand. This step uses energy (from ATP in eukaryotes or NAD+ in prokaryotes). The other enzymes have different roles: primase lays down RNA primers, polymerase fills in DNA and replaces primers, and helicase unwinds the double helix. Sealing the backbone between fragments is the job that ligase performs.