RNA (RiboNucleic Acid) are molecules used in cells as intermediary between genes.

There are many families of RNAs, each of which has a particular structure or function:

- messenger RNAs: these copy, at the level of each gene, a DNA sequence that will serve as a template

- ribosomal RNAs: they play a role in the binding of messenger RNAs

- transfer RNAs: they act as translators of the genetic sequence of the messenger RNA and allow their incorporation into proteins

An RNA polymerase is an enzyme that synthesizes (or polymerizes) RNA molecules by copying DNA (this is called DNA-dependent RNA polymerase) or by copying RNA (this is called RNA-dependent RNA polymerase).