Practice question

Electron microscopy, X-ray scattering and analytical ultracentrifugation support solenoid model where 30 nanometer fiber forms helix of nucleosomes approximated six per turn. Pitch about 11 nanometers corresponding to diameter of nucleosome disc itself. Six nucleosomes pack edge to edge per helical gyre producing packing ratio near forty-fold relative to naked DNA. Alternative two-start zigzag model proposes tetranucleosome repeating unit but still estimates similar density about six per 11 nanometer turn. Higher values eight to twelve would increase fiber diameter beyond 30 nanometer not observed. Therefore textbooks universally cite six nucleosomes per turn defining geometry.