The packaging of DNA inside the nucleus of a cell. As a typical DNA molecule is about 3 cm long, it must have tertiary structure (see protein) to enable it to fit inside a cell nucleus. Segments of DNA are wrapped around histones to form nucleosomes, with each nucleosome being separated from the next by a ‘linker’ that consists of some 50 base pairs of DNA. The nucleosomes themselves form a helix. Thus, DNA in cells can be regarded as a supercoil, i.e. a coiled coil. This supercoil picture accounts for much of the packing but further refinements are necessary to account for all of it.