Which DNA replication enzyme creates a small strip of RNA where DNA polymerase takes over to add DNA nucleotides?

Which DNA replication enzyme creates a small strip of RNA where DNA polymerase takes over to add DNA nucleotides?

• A. Primase
• B. DNA polymerase
• C. Ligase
• D. Topoisomerase

Answer: (A)

Primase makes a short RNA primer at the replication fork. DNA polymerase can only add nucleotides starting from an existing 3' end, so it needs this RNA primer to begin synthesis. Once the primer is laid down, DNA polymerase extends the DNA chain from that starting point. On the lagging strand, primers are laid repeatedly to start each Okazaki fragment, and later the RNA primers are replaced with DNA and the fragments joined. The other enzymes have different roles: DNA polymerase builds DNA, ligase seals nicks between fragments, and topoisomerase relieves torsional stress ahead of the fork.

Primase makes a short RNA primer at the replication fork. DNA polymerase can only add nucleotides starting from an existing 3' end, so it needs this RNA primer to begin synthesis. Once the primer is laid down, DNA polymerase extends the DNA chain from that starting point. On the lagging strand, primers are laid repeatedly to start each Okazaki fragment, and later the RNA primers are replaced with DNA and the fragments joined. The other enzymes have different roles: DNA polymerase builds DNA, ligase seals nicks between fragments, and topoisomerase relieves torsional stress ahead of the fork.