Transition of a polypeptide chain, helix-coil

The helix-coil transition of a polypeptide chain consisting of N monomers is usually described in terms of two parameters  

Small values of the cooperativity parameter, E, favor sharp helix-coil transitions which necessarily have very few segments. In terms of these parameters, the free energy per macromolecule may be simply written as 

The role of E in determining the sharpness of the transition may be graphically seen by considering the persistence length, V, which is the average number of monomers per helical segment. 

The (N/v) rigid segments are then confined to a volume of order, giving a rod density 

Excluded volume interactions will further decrease the density This is a strong argument suggesting that overlapping coils (semi-dilute solutions are necessary to obtain liquid crystalline order in solutions of worm-like macromolecules. 

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See also in sourсe #XX -- [ ]

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