Illustration of 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 attached to nucleotide bases. There are four bases: adenine (A), cytosine (C), guanine (G), and thymine (T), which are joined together by hydrogen bonds. DNA contains sections called genes that encode the body's genetic information.