LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY
DNA molecule. Plastic molecular model showing the structure of DNA (deoxyribonucleic acid). DNA is composed of two strands twisted into a double helix. Each strand consists of a sugar-phosphate backbone (on outside of helix) attached to nucleotide bases (horizontal, between strands). There are four different bases: guanine, cytosine, thymine and adenine. DNA contains sections called genes, which encode the body's genetic information.
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