Practice question

Electron microscopy of chromatin isolated in low ionic strength buffer reveals necklace-like organization: 11 nanometer particles spaced by thin linker DNA resembling beads on string. This configuration corresponds to extended primary chromatin fiber without H1-mediated coiling, exposing nucleosomes individually. Solenoid model describes 30 nanometer helix with six nucleosomes per turn, zig-zag describes two-start helix of 30 nanometer fiber, loop fiber denotes scaffold-anchored 300 nanometer domain. Beads-on-string visualization requires low salt to prevent folding, providing classic illustration of first level packing and histone octamer as repeating bead.