Figure 1 - High-resolution AFM images and tracing.

Data shown were taken on V4-grade mica with 12 mM Mg²⁺ (see Supplementary Information for other surfaces and salt concentrations). a, A 0.5  0.5 m AFM image (256  256 pixels) of 2,743-bp dsDNA deposited on mica; z-range 1.5 nm. b, Cross-sectional height profile of the DNA molecule, showing a half width at half maximum of only 2.5 nm. c, Detail of the square section indicated in a, showing also the chain of points determined by our automated image-analysis routine and illustrating the geometric quantities discussed in the text. Successive points are separated by ℓ = 2.5 nm. The end–end distribution K(R; L) is the probability distribution of real-space separation R among points separated by contour length L; in the example in the centre of the figure, we take L = 4  2.5 nm. The angle distribution G(; L) is the probability distribution of angles between tangents (short blue arrows) separated by L, which in the example on the right of the figure is 3  2.5 nm.