Base-pair structure of DNA, illustration. The double helix of the genetic molecule deoxyribonucleic acid (DNA) is at left, with an expanded schematic view of its nucleotide bases at right. The nucleotide bases (here represented by coloured hexagons) are cytosine (C, yellow), guanine (G, pink), adenine (A, orange) and thymine (T, green). The nucleotide base pairs are shown as coloured bars in the double helix at left. DNA is the genetic material that controls the growth and development of all living organisms. It is a double helix, with two spiralling sugar phosphate strands joined by nucleotide base pairs (coloured bars). The order of these nucleotides base pairs forms the genetic code. For this illustration without the nucleotide letter labels, see image C046/9208.