What are those structures that appear as ‘beads-on-string’ in the chromosomes when viewed under electron microscope?
(3) Base pairs
(2) Nucleosome is sub-microscopic sub-unit of chromatin which is formed by wrapping of DNA over a core of histone proteins. The term was coined by Oudet et. al, (1975). It is oblate structure with a length of 10 nm and a thickness of 5-5.7 nm. Its core is called nu-body. The latter is formed of four pairs of histone molecules. H2A, H2B, H3 and H4. DNA makes 1.75 turns over the