RNA Primer synthesis
and Primer-dependent DNA Synthesis

DNA polymerases are primer-dependent: they require an existing 3' end to begin nucleotide attachment. A short RNA Primer is synthesized chemically from the template strand by an RNA Primase. This provides the necessary 3' end, which is then extended by a DNA Polymerase.

Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2014 by Steven M. Carr