Which statement about DNA polymerase activity is true?

Which statement about DNA polymerase activity is true?

• A. They can begin synthesis on a template without a primer.
• B. They degrade RNA primers.
• C. They ligate Okazaki fragments.
• D. They can only add nucleotides to the 3' end.

Answer: (D)

DNA polymerases extend DNA by adding nucleotides to a pre-existing 3' hydroxyl group, moving in the 5' to 3' direction. Because elongation requires a 3' end to attach the next nucleotide, synthesis cannot start de novo on a plain template; a primer with a free 3' end must be present to begin replication. This makes the ability to add nucleotides only to the 3' end a universal truth about polymerase activity. The idea that they can start synthesis without a primer isn’t generally true, since a primer is needed to provide that initial 3' hydroxyl. While some polymerases can participate in primer removal or have exonuclease activities, those actions are not fundamental to the polymerase’s primary role and aren’t universal to all polymerases. And Okazaki fragment ligation is done by DNA ligase, not by the polymerase itself.

DNA polymerases extend DNA by adding nucleotides to a pre-existing 3' hydroxyl group, moving in the 5' to 3' direction. Because elongation requires a 3' end to attach the next nucleotide, synthesis cannot start de novo on a plain template; a primer with a free 3' end must be present to begin replication. This makes the ability to add nucleotides only to the 3' end a universal truth about polymerase activity. The idea that they can start synthesis without a primer isn’t generally true, since a primer is needed to provide that initial 3' hydroxyl. While some polymerases can participate in primer removal or have exonuclease activities, those actions are not fundamental to the polymerase’s primary role and aren’t universal to all polymerases. And Okazaki fragment ligation is done by DNA ligase, not by the polymerase itself.