RNA Primer synthesis
and Primer-dependent DNA Synthesis

Most DNA polymerases are primer-dependent, that is, they require a free 3' end to begin nucleotide attachment. In prokaryotes, a short RNA Primer is synthesized chemically from the template strand by an RNA Primase. This provides the necessary 3' end.

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