Deoxyribonucleic Acid (DNA) is the hereditary material in humans and almost all other organisms. Virtually every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
DNA is composed of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group, and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G), and cytosine (C). The order, or sequence, of these bases determines what biological instructions are contained in a strand of DNA.
The DNA double helix structure was discovered in 1953 by James Watson and Francis Crick, who used X-ray diffraction data collected by Rosalind Franklin and Maurice Wilkins. This helical structure allows DNA to efficiently store genetic information and pass it on to subsequent generations.