DNA molecule. Computer artwork of the molecular structure of DNA (deoxyribonucleic acid). The DNA molecule is composed of two strands twisted into a double helix. Each strand consists of an outer sugar-phosphate backbone (red) with nucleotide bases attached (blue). There are four different nucleotide bases. It is the varying sequence of these four bases along a DNA helix that forms the genetic code for that individual. A typical DNA molecule can contain a sequence that is many millions of bases long. The genetic code in DNA is the basis of all life on Earth.