Caption

DNA, computer artwork. DNA (deoxyribonucleic acid) consists of two strands (blue/purple) of sugar phosphates forming a double helix (spiral). The strands are held together by interactions between each strand's nucleotide bases (coloured rods). Although there are four types of nucleotide base, only two base pairings are usually possible (here, blue-green and red-yellow): adenine bonds to thymine, and cytosine bonds to guanine. This means each DNA strand is a reversed copy of the other, a vital part of DNA replication. The base sequence along the molecule is the inherited genetic code that controls growth and development. DNA, found in all living things, is stored in cell nuclei.