Cellular packaging of DNA. Illustration of the packaging of deoxyribonucleic acid (DNA) around proteins called histones (yellow). The DNA winds tightly into coils that wrap around the histones to form units called nucleosomes. Linker DNA joins the nucleosomes. Further coiling forms strands of chromatin, which condenses during cell division to form structures called chromosomes (blue, right). 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 artwork without labels, see image C023/8736.