Nucleosomes appear as 'beads-on-string' in the chromosome when viewed under electron microscope. The beads in 'beads-on-string" arrangement are complexes of histones and DNA. The bead plus the connecting DNA that leads to the next bead from the nucleosome. Nucleosome is the fundamental unit of organization on which the higherorder packaging of chromatin is built. The bead of each nucleosome contains eight histone molecules in which two copies each of H2A,H2B,H3 and H4 are found.
