DNA helix. Hands holding a model of part of the double helix of DNA (deoxyribonucleic acid), which is formed of spiralling paired strands of sugar phosphates that are linked by nucleotide base pairs. These pairs form struts, as on a ladder. The arrangement of the four types of nucleotide base along a helix of DNA forms the genetic code for protein synthesis and the functioning and growth of every living organism. DNA is found in cell nuclei.