What is the function of primase in DNA replication?

What is the function of primase in DNA replication?

• A. It unwinds the DNA helix to expose bases.
• B. It synthesizes an RNA primer to provide a 3'OH for DNA polymerase.
• C. It seals nicks between fragments.
• D. It adds nucleotides to the growing DNA strand.

Answer: (B)

Primase provides the RNA primer that starts DNA synthesis. DNA polymerases can’t begin a new strand from scratch; they need a preexisting 3' hydroxyl group to add nucleotides. Primase, a specialized RNA polymerase, lays down a short RNA primer complementary to the DNA template, supplying that 3'OH for DNA polymerase to extend. On the leading strand, one primer can suffice, while on the lagging strand multiple primers create Okazaki fragments that are later extended and eventually connected. After synthesis, the RNA primers are removed and replaced with DNA, and the fragments are joined. Primase doesn’t unwind the DNA (that’s helicase) or seal nicks (that’s ligase) or add nucleotides to the growing DNA strand itself (that’s DNA polymerase).

Primase provides the RNA primer that starts DNA synthesis. DNA polymerases can’t begin a new strand from scratch; they need a preexisting 3' hydroxyl group to add nucleotides. Primase, a specialized RNA polymerase, lays down a short RNA primer complementary to the DNA template, supplying that 3'OH for DNA polymerase to extend. On the leading strand, one primer can suffice, while on the lagging strand multiple primers create Okazaki fragments that are later extended and eventually connected. After synthesis, the RNA primers are removed and replaced with DNA, and the fragments are joined. Primase doesn’t unwind the DNA (that’s helicase) or seal nicks (that’s ligase) or add nucleotides to the growing DNA strand itself (that’s DNA polymerase).