Nucleosome

When we study the chromosome structure, we first see the whole chromosome. In its condensed metaphasic state it is about 1400nm thick.

The second step in examining the chromosome is to see the looped domains which form a fiber about 300nm thick. Here DNA and protein complexes are loosely looped around the central protein scaffold.

The third step in DNA packaging is the 30nm thick fiber which contains packed nucleosomes (see below).

Nucleosomes (10nm thick) are the last stage of packaging of DNA in chromosome. Here DNA double helix is rotated around the histone proteins.

The most common histone types are H2A, H2B, H3, H4.