The nucleus of each cell in our bodies contains approximately 1.8 metres of DNA in total, although each strand is less than one millionth of a centimetre thick. This DNA is tightly packed into structures called chromosomes, which consist of long chains of DNA and associated proteins. In eukaryotes, DNA molecules are tightly wound around proteins - called histone proteins - which provide structural support and play a role in controlling the activities of the genes. A strand 150 to 200 nucleotides long is wrapped twice around a core of eight histone proteins to form a structure called a nucleosome. The histone octamer at the centre of the nucleosome is formed from two units each of histones H2A, H2B, H3, and H4. The chains of histones are coiled in turn to form a solenoid, which is stabilised by the histone H1. Further coiling of the solenoids forms the structure of the chromosome proper.