What enzyme synthesizes the RNA primers required for DNA synthesis?

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

Answer: (A)

RNA primers are needed to start DNA synthesis because DNA polymerases can only add nucleotides onto an existing 3' end. The enzyme that creates these primers is primase, a specialized RNA polymerase. During replication, primase lays down a short RNA segment on each strand—the leading strand gets one primer to begin synthesis, while the lagging strand requires multiple primers to start each Okazaki fragment. After the primers are in place, DNA polymerase extends from them to build the new DNA. The RNA primers are later removed and replaced with DNA. Other enzymes have different roles: helicase unwinds the double helix, DNA polymerase synthesizes the new DNA, and ligase seals the nicks between Okazaki fragments. So primase is the enzyme responsible for synthesizing the RNA primers.