Nucleic acids, macromolecules made out of units called nucleotides. They are composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus. Nucleic acids come in two naturally occurring varieties: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in living organisms, all the way from single-celled bacteria to multicellular mammals like you and me. Some viruses use RNA, not DNA, as their genetic material, but aren’t technically considered to be alive (since they cannot reproduce without help from a host).