Thermodynamic anomaly and transitions in various states of poly (dG-dC)

Zimm and Bragg theory of helix\(\rightleftharpoons\) coil transition has been modified to explain order\(\rightleftharpoons\) order transition in polynucleotides, in particular \(B\rightleftharpoons Z\rightleftharpoons \psi (-)\rightleftharpoons\) coil transitions in poly (dG-dC) and poly (dG-me 5 dC). Lambda anomaly in specific heat measurements around the transition point have also been explained by a further modification of the same theory. Theoretical results are found to be in good agreement with the experimental data. The Nucleation parameter which determines the sharpness of transition and depends on the extent and strength of cooperativity, is consistent with the stabilization/destabilization of the ordered states under various environmental conditions, e.g. methylation of cytosine residue at C5 position or change in the cationic concentration of the solvent.