DNA molecule. Computer artwork of part of a strand of DNA (deoxyribonucleic acid). Atoms are depicted as balls and sticks and are colour-coded: nitrogen (blue), phosphorous and carbon (yellow) and oxygen (red). The surface of the molecule is represented as dots. DNA contains all the inherited instructions necessary to produce an organism. The DNA molecule is composed of two spiral strands of atoms forming a sugar-phosphate backbone, joined by the interactions of cross-linking nucleotide bases between them. It is the sequence of these bases that makes up the genetic code in the form of genes, specific segments of DNA.