Building block of DNA and RNA
The macromolecules DNA and RNA are made from four basic building blocks (ACGT for DNA and ACGU for RNA). These elementary building blocks of DNA and RNA are called 'bases'. However, when looking at one base at a time, the term base is often also used for just the flat group of atoms that is different between the bases. So in that case, the base consists of a base-plane, a sugar and a phosphate group. The bases are also found in small molecules with their own function. ATP for instance contains the adenosine base and stores energy.