Which enzyme seals the backbone after DNA fragments are synthesized?

Which enzyme seals the backbone after DNA fragments are synthesized?

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

Answer: (B)

Joining the discontinuous DNA fragments into one continuous strand requires sealing the sugar-phosphate backbone. The enzyme that does this is DNA ligase. After DNA polymerase has extended each fragment on the lagging strand and the RNA primers are removed, there are nicks between fragments. DNA ligase catalyzes the formation of phosphodiester bonds across these nicks, effectively linking the fragments together. In the process it uses energy from ATP (or NAD+ in some organisms). The other enzymes have different roles: polymerase builds DNA, primase lays down primers to start synthesis, and helicase unwinds the helix.

Joining the discontinuous DNA fragments into one continuous strand requires sealing the sugar-phosphate backbone. The enzyme that does this is DNA ligase. After DNA polymerase has extended each fragment on the lagging strand and the RNA primers are removed, there are nicks between fragments. DNA ligase catalyzes the formation of phosphodiester bonds across these nicks, effectively linking the fragments together. In the process it uses energy from ATP (or NAD+ in some organisms). The other enzymes have different roles: polymerase builds DNA, primase lays down primers to start synthesis, and helicase unwinds the helix.