ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
DNA. Computer artwork of a deoxyribonucleic acid (DNA) molecule (right) and a historical drawing of a male figure by Leonardo da Vinci (1453-1519). DNA is composed of two strands twisted into a double helix. Each strand consists of a sugar- phosphate backbone (larger beads) attached to nucleotide bases (smaller beads). 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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