What is the role of primase during DNA replication?

• A. Primase adds DNA nucleotides to start synthesis.
• B. Primase unwinds the double helix.
• C. Primase seals nicks between Okazaki fragments.
• D. Primase synthesizes an RNA primer to provide a 3'OH for DNA polymerases to begin synthesis.

Answer: (D)

Primase raises the starting point for DNA synthesis by laying down a short RNA primer. DNA polymerases can only extend from an existing 3' hydroxyl group, so they can’t begin synthesis on a bare strand. Primase provides that 3'OH, allowing DNA polymerases to add DNA nucleotides. On the leading strand one primer is enough, while on the lagging strand multiple primers are needed to start each Okazaki fragment. Later, the RNA primer is removed and replaced with DNA, and a separate enzyme seals the remaining nicks. This clarifies why primase’s job is to create the RNA primer for DNA polymerases to begin copying the DNA.