Which statement about RNA primers is true?

Which statement about RNA primers is true?

• A. They are composed of RNA nucleotides and provide a starting point for DNA synthesis
• B. They are DNA sequences that initiate replication
• C. They are proteins that unwind DNA
• D. They are ligases that seal fragments

Answer: (A)

RNA primers are short RNA nucleotide sequences laid down by primase to provide a starting point for DNA synthesis. DNA polymerases cannot begin a new strand from scratch—they require a free 3'-OH to add nucleotides. The primer supplies that initial point, allowing polymerase to extend the DNA strand. After synthesis starts, the RNA primer is removed and replaced with DNA, and any gaps are sealed by ligase on the backbone. The other statements don’t fit because replication initiation involves broader features like origins of replication and helicase activity, not primers themselves; primers are RNA, not DNA sequences; they are not proteins that unwind DNA; and they are not ligases that seal fragments.

RNA primers are short RNA nucleotide sequences laid down by primase to provide a starting point for DNA synthesis. DNA polymerases cannot begin a new strand from scratch—they require a free 3'-OH to add nucleotides. The primer supplies that initial point, allowing polymerase to extend the DNA strand. After synthesis starts, the RNA primer is removed and replaced with DNA, and any gaps are sealed by ligase on the backbone.

The other statements don’t fit because replication initiation involves broader features like origins of replication and helicase activity, not primers themselves; primers are RNA, not DNA sequences; they are not proteins that unwind DNA; and they are not ligases that seal fragments.