Nucleosomes are the fundamental repeating units of eukaryotic chromatin, with the exception of mature sperm. They are the smallest structural unit of eukaryotic DNA packaging, fundamental to the structure of the chromosome(s) inside the cell nucleus and can play a role in controlling gene expression. They are made up of about 146 base pairs of DNA and four pairs of proteins called histones, and resemble "beads on a string of DNA" when observed with an electron microscope (a 10nm fiber). The nuc… (More on Nucleosome)