Double Helix
The structure of DNA, in which two antiparallel polynucleotide strands wind around a common axis.
Formula / equation
10.5 base pairs per turn
Unit
nm
In depth
The sugar–phosphate backbones lie on the outside and the hydrogen-bonded base pairs stack in the core, where base stacking contributes as much stability as the hydrogen bonds. The 2 nm-wide helix has major and minor grooves through which proteins read the sequence.
Examples in the real world
Watson and Crick's 1953 model, built on Franklin's X-ray diffraction photograph.