A superhelix is a molecular structure in which a helix is itself coiled into a helix. 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:
About the writhing number, mathematician W. F. Pohl says:
Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship:
:L= T + W,
where L is the linking number, W is the writhe and T is the twist of the coil.
The linking number refers to the number of times that one strand wraps around the other. In DNA this property does not change and can only be modified by specialized enzymes called topoisomerases.