What is the role of primase in DNA replication?

What is the role of primase in DNA replication?

• A. It unwinds the DNA double helix
• B. It proofreads newly synthesized DNA
• C. It elongates the DNA strand
• D. It synthesizes RNA primer on both strands which helps DNA polymerase know where to bind

Answer: (D)

Primase’s job is to lay down short RNA primers that start DNA synthesis. DNA polymerases can’t begin a new strand from scratch; they need a 3′-OH end to add nucleotides onto. Primase, a RNA polymerase, provides exactly that starting point on both strands. On the leading strand, one primer suffices for continuous synthesis; on the lagging strand, primers are made repeatedly to create Okazaki fragments that are later extended and joined. These primers give DNA polymerase the spot to begin adding DNA nucleotides. The other options describe different enzymes or activities: unwinding the DNA is done by helicase, proofreading is done by exonuclease activity, and elongating the DNA strand is the job of DNA polymerase itself.

Primase’s job is to lay down short RNA primers that start DNA synthesis. DNA polymerases can’t begin a new strand from scratch; they need a 3′-OH end to add nucleotides onto. Primase, a RNA polymerase, provides exactly that starting point on both strands. On the leading strand, one primer suffices for continuous synthesis; on the lagging strand, primers are made repeatedly to create Okazaki fragments that are later extended and joined. These primers give DNA polymerase the spot to begin adding DNA nucleotides. The other options describe different enzymes or activities: unwinding the DNA is done by helicase, proofreading is done by exonuclease activity, and elongating the DNA strand is the job of DNA polymerase itself.