Which statement best describes the role of primase?

Which statement best describes the role of primase?

• A. It unwinds DNA
• B. It synthesizes RNA primer from scratch using DNA as a template
• C. It seals nicks in the backbone
• D. It transcribes mRNA

Answer: (B)

In DNA replication, primase acts as an RNA polymerase that lays down a short RNA primer from scratch, using the DNA as a template. This primer provides a 3' hydroxyl group for DNA polymerase to begin synthesizing the new strand, since DNA polymerases cannot start a new chain on their own. After synthesis, the primer is removed and replaced with DNA, and the backbone is sealed by ligase. For contrast, unwinding the DNA is done by helicase, and transcribing mRNA is carried out by RNA polymerase during gene expression, not replication.

In DNA replication, primase acts as an RNA polymerase that lays down a short RNA primer from scratch, using the DNA as a template. This primer provides a 3' hydroxyl group for DNA polymerase to begin synthesizing the new strand, since DNA polymerases cannot start a new chain on their own. After synthesis, the primer is removed and replaced with DNA, and the backbone is sealed by ligase. For contrast, unwinding the DNA is done by helicase, and transcribing mRNA is carried out by RNA polymerase during gene expression, not replication.