DNA helix. Computer artwork of part of a strand of DNA (deoxyribonucleic acid). The DNA molecule has a double helix arrangement, being composed of two right-handed spiral strands of sugar phosphates. These strands are held together by complementary pairs of four cross-linking nucleotide bases (geometric shapes): adenine, cytosine, guanine and thymine. The sequence of bases makes up the unique genetic code of every individual organism.