MODEL RELEASED. Teenager building DNA model. Teenage boy at home using chemical modelling units to construct the double helix of DNA (deoxyribonucleic acid). This macromolecule, found in cell nuclei, comprises two sugar phosphate strands in a twisting helical shape. These strands (black and white) have nucleotide bases (coloured) that bond to each other and join the two strands together. It is the sequence of these nucleotide bases that forms the genetic code. There are four bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The complementary pairs (blue and yellow; red and green) are G-C and A-T. For DNA replication, see C024/0360.