The intrinsic nature of secondary structures

The formation of secondary stractures requires cooperative behavior of adjacent monomers, i.e, in addition to pairwise repulsion, information about the relative position of the monomers to each other in the chain is necessary to effectively model the competition between noncovalent monomeric attraction and short-range repulsion due to volume 

Two examples of circles with different radii of curvature. The small circle is defined by the three consecutive monomers 8,9, and 10 in which case its radius is called the local radius of curvature. From (243). 

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