Describe the structure of a nucleosome with the help of a well-labelled diagram.

Explanation

A nucleosome is a structure in chromosomes or bundled DNA. The negatively charged DNA is wrapped around positively charged histone octamer to form a structure called nucleosome. Each nucleosome has a core particle, DNA, and a linker protein. The proteins in the core particle and linker proteins are called histones. It consists of 8 histones (octamer). The DNA will wrap around the core particle about 1.65 times and is secured by the linker protein. A typical nucleosome consists of 200 bp of DNA helix. It consists of four types of proteins which occur in pairs : `H_2A, H_2B, H_3 and H_4`. About 200 bases of DNA are involved with each nucleosome. Humans have 23 pairs of chromosomes. DNA winds around the core (`1^3//4` turn involving approximately 146 base pairs), two successive nucleosomes are joined together by linker DNA (approximately 80 BP) `H_1`. histone holds the entire complex by connecting the linker DNA at the points of entry and exit. There are repeating units in chromatin fibre like beads on string.