Helix-Coil Transition and Degree of Polymerization of Double Chains of Complementary Homopolynucleotides

Abstract

Thermal transitions, of DNA type molecules of degree of polymerization from 3 to 10 and larger than 100 are studied, using three models, that is, all or none model, zipper model and broken ladder model. Calculations are made for various values of the ratio of hydrogen bond energy to the sum of hydrogen bond energy and stacking energy. It is shown that this ratio markedly affects the dependence of the transition temperature upon the degree of polymerization. Therefore, the information on this ratio may be obtained from experimental studies of the chain length dependence of thermal transition. In each of three models for large values of degree of polymerization, it is shown that the reciprocal of the transition temperature is a linear function of the reciprocal of the degree of polymerization of a molecule. It is also shown that even in the case of small degree of polymerization three models give markedly different melting curves if this ratio is large.