The typical length of an RNA primer is 5-10 nucleotides.

• A. 15-20 nucleotides
• B. 5-10 nucleotides
• C. 1-2 nucleotides
• D. 50-60 nucleotides

Answer: (B)

RNA primers provide the starting point for DNA synthesis during replication, so their length must strike a balance: long enough to give DNA polymerase a reliable 3' OH to extend from, but short enough to be efficiently removed and replaced during processing. In practice, primers are typically about five to ten nucleotides long. This short length makes them easy to start synthesis without committing to a long RNA segment that would need extra steps to remove, yet long enough to stably base-pair with the template and guide the polymerase.

If primers were much longer, like fifteen to twenty nucleotides, they would create longer RNA segments that are more cumbersome to remove and replace, potentially slowing replication and complicating processing on the lagging strand. If primers were extremely short, such as one or two nucleotides, they would be unstable and unlikely to provide a reliable starting point for polymerase activity. A primer in the range of five to ten nucleotides fits the needs of efficient initiation and smooth removal, making it the best answer.