Genetic material is used to store the genetic information of an organic life form. For all currently known living organisms, the genetic material is almost exclusively Deoxyribonucleic Acid (DNA). Some viruses use (Ribonucleic Acid) RNA as their genetic material. The first genetic material is generally believed to have been RNA, initially manifested by self-replicating RNA molecules floating on bodies of water. This hypothetical period in the evolution of cellular life is known as the RNA world. This hypothesis is based on RNA's ability to act both as genetic material and as a catalyst, known as ribozyme or a ribosome. However, once proteins, which can form enzymes, came into existence, the more stable molecule DNA became the dominant genetic material, a situation continued today. Not only does DNA's double-stranded nature allow for correction of mutations but RNA is inherently unstable. Modern cells use RNA mainly for the building of proteins from DNA instructions, in the form of messenger RNA, ribosomal RNA, and transfer RNA. Both RNA and DNA are macromolecules composed of nucleotides, of which there are four available in each molecule. Three nucleotides compose a codon, a sort of "genetic word", which is like an amino acid in a protein. The codon-amino acid translation is known as Translation (genetics).
