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 attached to a non-histone protein scaffold. At the fourth structural level, the scaffold forms a spiral 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 with distinctive size and morphology. The chromatin in any single chromosome appears to be a single, continuous DNA helix.

Figure © 2000 by Griffiths et al. ; text © 2014 by Steven M. Carr