The enzyme responsible for creating the primer that allows DNA replication to start is called RNA primase. RNA primase synthesizes a short RNA primer on the DNA template strand, providing the starting point for DNA polymerase to begin DNA synthesis. Without this primer, DNA polymerase cannot add nucleotides to initiate replication because it can only extend an existing strand, not start one from scratch.
In more detail, RNA primase builds the RNA primers at specific initiation sites on the single-stranded DNA during replication. These RNA primers are typically about 10-12 nucleotides long and serve as the 3' hydroxyl (-OH) group attachment site for DNA polymerase to add DNA nucleotides. After the RNA primer is synthesized, DNA polymerase extends the primer by adding DNA nucleotides, eventually replacing the RNA with DNA to complete the strand.
Additionally, in eukaryotes, the enzyme complex Polα-primase plays a role by first synthesizing the RNA primer and then extending it with a short stretch of DNA before more accurate DNA polymerases continue replication.
Thus, the creation of the primer that allows DNA replication to start is primarily catalyzed by RNA primase.