What is the function of RNA primers in replication, and what happens after their job is done?

• A. Primers provide 5' phosphate ends for ligation.
• B. Primers provide 3' OH ends for DNA synthesis; after synthesis, RNA primers are removed and gaps filled with DNA and sealed.
• C. Primers remain in place as final segments of DNA.
• D. Primers degrade the RNA to prevent interference.

Answer: (B)

DNA replication hinges on giving DNA polymerase a starting point to add nucleotides. RNA primers provide a short 3' hydroxyl group that polymerase can extend from, enabling synthesis of a new DNA strand. Primase lays down these primers, and DNA polymerase extends from them in the 5' to 3' direction. On the leading strand, a single primer suffices, while the lagging strand uses multiple primers to create Okazaki fragments.

After the new DNA is copied, the RNA primers are removed and the resulting gaps are filled in with DNA. The remaining nicks are then sealed by DNA ligase to produce a continuous DNA strand. This is why primers are essential to start synthesis but are not part of the final sequence; they’re replaced by DNA during replication.

The other options don’t fit this role: primers don’t provide 5' phosphate ends for ligation, they aren’t retained as final DNA segments, and they aren’t simply degraded to prevent interference—their RNA is removed and replaced with DNA before sealing the backbone.