DNA molecule. Computer artwork showing a double stranded DNA (deoxyribonucleic acid) molecule. DNA is composed of two strands twisted into a double helix. Each strand consists of a sugar-phosphate backbone (purple and silver) attached to nucleotide bases (bars). There are four bases: adenine, cytosine, guanine and thymine. The bases are joined together by hydrogen bonds (rods, between spheres). DNA contains sections called genes that encode the body's genetic information.