17. DNA polymerase III can only add nucleotides to an existing chain, so is required. a). an RNA primer b). DNA polymerase I c). helicase d). a DNA primer Answer:a

## Step 1<br />The problem is about the process of DNA replication, specifically the role of DNA polymerase III. DNA polymerase III is an enzyme that adds nucleotides to an existing chain during DNA replication.<br /><br />## Step 2<br />However, DNA polymerase III cannot initiate a new chain; it can only add nucleotides to an existing chain. This means that there must be a starting point for the new chain.<br /><br />## Step 3<br />This starting point is provided by an RNA primer. An RNA primer is a short segment of RNA that serves as a starting point for DNA synthesis.<br /><br />## Step 4<br />The RNA primer is synthesized by an enzyme called primase. Once the RNA primer is in place, DNA polymerase III can begin adding nucleotides to the chain.