Super
Coiling of DNA: A summary
The DNA double helix
(red) wraps around a Nucleosome.
Six nucleosomes form one turn of a Solenoid. Loops of
solenoid coils are attached to a non-histone
protein Scaffold.
The scaffold is
coiled, and is in turn coiled as a supercoil that
constitutes a single chromatin fiber.
During metaphase
of the cell cycle, the chromatin condenses
in an orderly manner to form a
microscopically-visible chromosome (comprising
two identical chromatids
joined at a centromere) with
distinctive size and morphology. The chromatin in
any single chromosome
appears to be a single, continuous DNA helix
Super-coiling of DNA resembles the coiling of
an unfastened rope for throwing, as in the following
series showing the coiling of a rope as a
maximally-compact, repetitive, organized "Bird's
Nest or Daisy Chain"
structure. Note that in the final photo, casting the
loose bight at bottom allows the coiled rope to pay
out smoothly, just as the DNA molecule
unwinds without tangling.
Top figure © 2000 by
Griffiths et al.; "Bird's Nest" figures ©2013
by bcworkz; text © 2014 by Steven
M. Carr