With the help of a suitable diagram describe the structure of a nucleosome.

Explanation

(1) Nucleosome is a small darkly staining body present in the nucleus of an eukaryotic cell.
(2) It is located in the chromatin network and appears as beads on string of chromatin fibres under an electron microscope.
(3) Each nucleosome is formed of DNA which is negatively charged and histone octamer which is positively charged.
(4 ) Histone octamer is made up of eight molecules of histones, two each of `H_(2)A, H_(2)B, H_(3) and H_(4)`
(5) Adjacent nucleosomes are linked by fragments called linker DNA. These are 54bp long.
(6) Nucleosome fibre is the structure formed by the condensation of 'beads on string' structure. This fibre is about 10 nm in diameter.
(7) Another type of nucleosome fibre is called solenoid fibre which is a thin and long fibre having a diameter of 30 nm.
(8) Nucleosomes are visible only at the time of interphase.
(9) Each nucleosome contains about 200bp of DNA helix.