Secondary & Tertiary chromosome
The DNA double helix is wrapped twice
around a octamer core unit
that comprises eight histone proteins.
These nucleosomes are
separated by a run of spacer DNA complexed
with a single histone H1 unit.
At the tertiary level [right], six nucleosomes form a
spiral organized around
their H1 histone spacers, to
form a solenoid.
Figure © 2000 by
al. ; text © 2008 by Steven M.