What marks the transition from primer to DNA synthesis?

What marks the transition from primer to DNA synthesis?

• A. The 3' end of the RNA primer serves as the starting point for DNA synthesis by DNA polymerase
• B. The primer is extended by RNA polymerase
• C. The primer is removed before DNA synthesis begins
• D. The RNA primer is degraded and no longer used

Answer: (A)

DNA synthesis by polymerases requires a pre-existing 3' hydroxyl group to start adding nucleotides. The RNA primer laid down by primase provides that 3' end, so DNA polymerase can begin extending the new DNA strand from that point. When the 3' end of the RNA primer serves as the starting point for DNA synthesis, the process shifts from primer setup to true DNA synthesis. After synthesis proceeds, the RNA primer is removed and replaced with DNA. The primer isn’t extended by RNA polymerase, and it isn’t removed before any synthesis begins.

DNA synthesis by polymerases requires a pre-existing 3' hydroxyl group to start adding nucleotides. The RNA primer laid down by primase provides that 3' end, so DNA polymerase can begin extending the new DNA strand from that point. When the 3' end of the RNA primer serves as the starting point for DNA synthesis, the process shifts from primer setup to true DNA synthesis. After synthesis proceeds, the RNA primer is removed and replaced with DNA. The primer isn’t extended by RNA polymerase, and it isn’t removed before any synthesis begins.