DNA stands for deoxyribonucleic acid. It is a molecule that contains the genetic instructions used in the development and function of all living organisms. DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases pair up in a specific way (A with T, and C with G) to form the rungs of a twisted ladder-like structure called a double helix. The sequence of these bases determines the genetic code that is passed down from one generation to the next. DNA is found in the nucleus of cells in all living organisms.