RNA

Ribonucleic acid (RNA) is a molecule found in all cells, comprised of many individual units of nucleic acid. It differs from Deoxyribonucleic acid (DNA) in that it only contains a single, not double strand, and substitutes uracil for thymine. The primary role of RNA is to transfer a copy of the information coded in DNA to a ribosome to be expressed as a protein. It is also a component of the ribosome itself.

The polio virus is an example of an organism which contains only RNA to carry its genetic information.