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# Long description

The diagram shows the dimensions of the chromosome components from the bare, unfolded DNA double helix of diameter 2 nanometres to the highly compacted mitotic chromosome. The double helix is wound around a histone-protein complex, forming a succession of nucleosomes - an extended chromatin strand of width about 11 nanometres, The strand is wound into a spiral structure of width 30 nanometres, which is looped and condensed into a structure 300 nanometres wide, characteristic of cells during interphase. Further spiralling and condensation occurs in cells preparing to divide, when each member of a pair of chromatids has a diameter of about 700 nanometres.