Cellular packaging of DNA. Illustration of the packaging of deoxyribonucleic acid (DNA) from chromosome (centre left) to the DNA strand form and its nucleotide base pairs (upper right). Between these states, the DNA winds tightly into coils that wrap around protein structures called histones to form units called nucleosomes (both at lower right). Further coiling forms strands of chromatin, which condenses during cell division to form structures called chromosomes. DNA is found in the cell nucleus, shown in a cutaway view of a cell at far left. DNA forms the genetic basis of nearly all living organisms. The DNA in a cell nucleus (less than 0.1 millimetres across) is over 2 metres in length when unravelled. For this illustration without labels, see image C046/9211.