DNA is the genetic material found in the nucleus of a cell. It is a polymer: a very long molecule made by joining many small repeating units together in a chain. The repeating units in DNA are called nucleotides.
Because DNA is a polymer, it can be extremely long, and it can store a huge amount of information in the order of its nucleotides. In a cell the long DNA molecules are coiled up into chromosomes.
Scientists and students build models of DNA, for example from coloured beads or paper shapes. A model shows how the units join in a chain, but it is a simplified version of the real molecule.
