Computer graphics image of DNA, showing its double helix structure & base pairing. DNA (deoxyribonuc- leic acid) consists of two linked strands of nucleotides (dark blue & purple), coiled into a helix. The strands are joined by the hydrogen bonding of pairs of organic bases (light blue & yellow) on adjacent nucleotides. Each nucleotide contains the sugar deoxyribose & one of four bases: thymine (T), adenine (A), cytosine (C), & guanine (G). T pairs up only with A, C with G. The genetic information is determined by the ordering of these pairs. The image shows the B form of DNA (B-DNA).