Super Coiling of DNA
The DNA double helix wraps around a nucleosome. Six nucleosomes form one
turn of a solenoid. Loops of solenoid coils are
a non-histone protein scaffold.
At the fourth level, the scaffold forms a spiral supercoil, which constitutes a chromatin fiber. During metaphase of the cell cycle, the
chromatin condenses in an orderly manner to form
microscaopically-visible chromosomes with distinctive sizes and
morphologies. The chromatin that
makes up a single chromosome appears
to be a single, continuous DNA helix.
Figure © 2000 by
al. ; text © 2008 by Steven M.