Question

DNA replication in vivo requires a primer with a free 3' end. What molecular species provides this 3' end, and how is it provided?"

A) tRNA; provided by RNA polymerase
B) mRNA; provided by reverse transcriptase
C) rRNA; provided by ligase
D) RNA primer; provided by primase

Answer 1

The correct option in the final answer is D. The molecular species that provides the free 3' end for DNA replication is an RNA primer, which is synthesized by the enzyme primase.

Step-by-step explanation:

DNA Replication Primer and Enzyme

In the process of DNA replication, a primer is necessary to provide a free 3' hydroxyl (-OH) group for DNA polymerase to begin adding nucleotides. The specific molecular species that provides this 3' end is an RNA primer, which is short, complementary to the DNA strand, and facilitates the start of DNA synthesis.

This RNA primer is synthesized by an enzyme called primase, which is an RNA polymerase capable of adding RNA nucleotides against a DNA template without needing a pre-existing 3' end. Therefore, the correct option for the molecular species that provides the 3' end and the enzyme that synthesizes it is: D) RNA primer; provided by primase.