Practice question

B-form DNA double helix diameter measured by Franklin Wilkins X-ray diffraction patterns approximates 2.0 nanometers, corresponding to distance across base pair plus phosphate backbone van der Waals radii. This baseline dimension explains how 147 base pairs wrapped around 11 nanometer octamer achieves first level compaction. Subsequent levels: nucleosome 11 nanometer, solenoid 30 nanometer, looped scaffold 300 nanometer, metaphase chromatid 700 nanometer represent stepwise coiling. Recognizing 2 nanometer starting point underscores approximately seven-fold linear compaction achieved at nucleosome level alone before higher-order scaffolding multiplies packing ratio toward functional chromosome formation during mitosis.