Superhelical Density and Energetics of Supercoiling

Superhelical density, a, is a term frequently used and is defined as the average number of superhelical turns per helical turn of DNA  

Osp refers to the inherent specific linking difference and the value of Osp can be different from that of a. 

The free energy of supercoiling is proportional to the square of the linking number difference in the DNA  

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