DNA helix. Hand holding a model of a double helix of DNA (deoxyribonucleic acid), which is formed of spiralling paired strands of sugar phosphates that are linked by nucleotide base pairs. There are four bases: adenine, thymine, guanine & cytosine (coloured links) that when paired form struts, as on a ladder. The arrangement of the bases along a helix of DNA is the genetic code for protein synthesis and the functioning & growth of every living organism. DNA is found in cell nuclei.