Chromatin: The formation of chromosomes Chromatin is packed into chromosomes during mitosis. We will look at the steps from interphase to metaphase There are several levels of organisation in terms of chromatin folding? Free DNA 2nm Formation of the nucleosome: The DNA strand wraps around a core of eight histones (H2A, H2B, H3, H4: x2) 1.65 times. Also known as ?beads-on-a-string? and is the basic chromatin structure. 10nm An H1 histone tails binds on the outside of the coil on each nucleosome unit, now chromatosome units. Further condensing occurs: 30nm Interactions between: Interactions between chromatosomes (nucleosomes and H1 histones) leads to more folding of the 30nm fibres, creating a thicker fibre. 30nm