DNA, or deoxyribonucleic acid, is a molecule that carries the genetic instructions for all living organisms. It is composed of two long strands that twist together to form a double helix. Each strand is made up of smaller units called nucleotides, which contain a sugar, a phosphate group, and a nitrogenous base. The sequence of these bases encodes the information needed for growth, development, and functioning. In humans and many other organisms, DNA is found in the nucleus of cells. It is organized into structures called chromosomes, which ensure that genetic information is accurately copied and passed on during cell division. DNA plays a crucial role in heredity, as it is inherited from parents and determines traits in offspring.