Deoxyribonucleic acid (DNA) is the hereditary material in humans and in every other organism on Earth, apart from some viruses.
It is a polymer, consisting of four different monomers, called nucleotides, shaped as a double helix, which functions as a code, or blueprint, for the manufacture of enzymes and RNA within cells and thus controls cell division and metabolism.
The DNA molecule is made up of two long chains of nucleotides running in opposite directions (anti-parallel). Part of each nucleotide is a sugar, another part is called a base.
There are four different bases; this gives the four different DNA monomers and it is the sequence of bases which encodes information - "the genetic code"- which specifies the sequence of amino acids within proteins.
Because some of the sequences encode for proteins which result in the switching on or off of other sequences, DNA can act over time, allowing, for example, embryonic development.
DNA is found in the chromosomes and, except for identical twins, or clones, is unique to each individual.