Which enzyme starts an RNA chain from scratch?

Which enzyme starts an RNA chain from scratch?

• A. DNA polymerase
• B. Helicase
• C. Ligase
• D. Primase

Answer: (D)

The task here is about who can start an RNA chain from nothing during replication. Primase is the enzyme that does this: it synthesizes a short RNA primer de novo, using ribonucleotides, to provide a free 3' hydroxyl group for DNA polymerase to extend. DNA polymerases, by contrast, cannot start a new strand on their own; they need that existing primer to begin adding DNA nucleotides. Helicase’s job is to unwind the double helix, not to make primers. Ligase seals nicks after synthesis. So primase uniquely provides the initial RNA segment that kick-starts synthesis, making it the correct choice.

The task here is about who can start an RNA chain from nothing during replication. Primase is the enzyme that does this: it synthesizes a short RNA primer de novo, using ribonucleotides, to provide a free 3' hydroxyl group for DNA polymerase to extend. DNA polymerases, by contrast, cannot start a new strand on their own; they need that existing primer to begin adding DNA nucleotides. Helicase’s job is to unwind the double helix, not to make primers. Ligase seals nicks after synthesis. So primase uniquely provides the initial RNA segment that kick-starts synthesis, making it the correct choice.