The sites where new nucleotides are added during DNA replication are called ______.

• A. Initiation Site
• B. Origin
• C. Replication Fork
• D. Primer

Answer: (C)

DNA synthesis occurs at the replication fork, the region where the double helix is unwound and the template strands are exposed. Here, DNA polymerases add nucleotides to the 3' end of the growing strand, using each parental strand as a template. The leading strand is built continuously toward the fork, while the lagging strand is synthesized in short Okazaki fragments away from the fork, each fragment starting with a short RNA primer laid down by primase. The origin marks where replication begins, not the ongoing site of nucleotide addition, and a primer provides the starting point for synthesis but the actual addition of nucleotides happens at the replication fork.