DNA - deoxyribonucleic acid - is the molecule that stores and carries the genetic information used to control the growth, development, functioning and reproduction of all living organisms. It is the hereditary material within each cell. Within eukaryotic organisms, the DNA within the nucleus of the cell is organized into linear structures called chromosomes. The information in DNA is stored in the form of a concise code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). It is the sequence of these base pairs that determines the structure of every protein in the body, and it is what makes each person unique. Human DNA consists of a sequence of about 3 billion bases, but surprisingly more than 99 percent of those bases are the same in all people. DNA structure is in the form of the now-famous double helix. The spiral helices of the DNA consist of 2 backbones of sugar and phosphates, connected to one another by the base pairs, in structures that look somewhat like rungs on a ladder.