Each cell in your body has around 2 metres of DNA inside. DNA is a very long chemical called a polymer, that is built from lots of individual nucleotides, or bases. The order that these bases come in encodes genes, which are the assembly instructions for all the proteins that make living things function. DNA is double-stranded, with one strand encoding the information and the other strand acting as a backup copy in case of damage. DNA twists in a spiral, with about 11 pairs of bases per full rotation.