Regarding the 3' end of the RNA primer, which statement is true?

Regarding the 3' end of the RNA primer, which statement is true?

• A. The 3' end has no role in initiating synthesis
• B. The 3' end is the 5' end of the primer
• C. The 3' end provides a free hydroxyl group for DNA polymerase to add nucleotides
• D. The 3' end is removed before replication

Answer: (C)

In DNA replication, DNA polymerase can only add nucleotides to an existing strand that has a free 3' hydroxyl group. The RNA primer laid down by primase provides this exact 3' end, enabling DNA polymerase to extend the new DNA chain by attaching nucleotides to that 3' OH. Synthesis proceeds in the 5' to 3' direction, so growth occurs from the primer’s 3' end. On the leading strand, one primer suffices for continuous synthesis; on the lagging strand, primers mark the start of each Okazaki fragment. After synthesis, the RNA primers are removed and replaced with DNA, and the gaps are sealed. So the statement that the 3' end provides a free hydroxyl group for DNA polymerase to add nucleotides is the correct description. The 3' end is not the 5' end, and it isn’t removed before replication begins; primer removal happens afterward during processing of the new DNA.

In DNA replication, DNA polymerase can only add nucleotides to an existing strand that has a free 3' hydroxyl group. The RNA primer laid down by primase provides this exact 3' end, enabling DNA polymerase to extend the new DNA chain by attaching nucleotides to that 3' OH. Synthesis proceeds in the 5' to 3' direction, so growth occurs from the primer’s 3' end. On the leading strand, one primer suffices for continuous synthesis; on the lagging strand, primers mark the start of each Okazaki fragment. After synthesis, the RNA primers are removed and replaced with DNA, and the gaps are sealed. So the statement that the 3' end provides a free hydroxyl group for DNA polymerase to add nucleotides is the correct description. The 3' end is not the 5' end, and it isn’t removed before replication begins; primer removal happens afterward during processing of the new DNA.