Cellular packaging of DNA. Artwork of a strand of the genetic material DNA (deoxyribonucleic acid, right) unwound from a chromosome (centre). The chromosome is a condensed form of DNA that forms during cell division. DNA is located within the nucleus of cells in a form called chromatin, and a cell and its nucleus are shown at upper left. The DNA in a cell nucleus, which is less than 0.1 millimetres across, is over 2 metres in length when unravelled. This model of a DNA strand shows the double helix structure of two spiralling sugar phosphate strands joined by pairs of nucleotide bases (coloured bars).