Superhelix

This is significant to both proteins and genetic material, such as overwound circular DNA.

The earliest significant reference in molecular biology is from 1971, by F. B. Fuller: A geometric invariant of a space curve, the writhing number, is defined and studied.

For the central curve of a twisted cord the writhing number measures the extent to which coiling of the central curve has relieved local twisting of the cord.

[2]Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship: where Lk is the linking number, W is the writhe and T is the twist of the coil.

In DNA this property does not change and can only be modified by specialized enzymes called topoisomerases.