Illustration of a DNA (deoxyribonucleic acid) molecule (left) replicating. DNA is composed of two strands twisted into a double helix, held together by bonds between paired nucleotide bases. Before replication, the strands separate from each other. Each strand then each acts as a template for the formation of two new DNA molecules (upper and lower right). This is known as semiconservative replication. DNA contains sections called genes, which encode the body's genetic information.