Telomeres and Replication: Part 1

During replication, DNA polymerase can only add nucleotides to the 3′ -OH group of an existing DNA or RNA strand.

Initiating replication of a new DNA strand requires an enzyme called primase, which uses a template DNA strand to synthesize a stretch of RNA called an RNA primer. The RNA primer forms just upstream of the start of replication and provides a place for DNA polymerase to begin replication.