Deoxyribonucleic acid (DNA) is the molecule that contains all genetic instructions for living organisms. DNA is formed into a double helix, and most DNA is found in the nucleus of a cell, but some can also be found in its mitochondria.
DNA molecules consist of nucleotides that are linked to each other in a chain. Each nucleotide has three components: one sugar (deoxyribose), one phosphate, and one of the four bases: adenine (A), cytosine (C), guanine (G), and thymine (T). All nucleotides contain the same sugar and phosphate backbone. The genetic information comes from the order in which the nucleotides appear.
DNA needs not only to store genetic information, but also to identically reproduce this information in order to pass it on to the next generation.