Caption

DNA molecule. Computer artwork representing the structure of a DNA (deoxyribonucleic acid) double helix. The helix molecule carries the genetic code, which controls and transmits an organism's hereditary traits. It is composed of two twisting strands (white/blue) of sugar-phosphate molecules, linked by complementary pairs of nucleotide bases (coloured spheres). There are four types of nucleotide base; adenine, guanine, cytosine and thymine. The sequence of base pairs, arranged in discrete segments known as genes, determines the genetic code.