The Lifsonmdash;Zimms' theory for helix to random coil transition has been extended tonhyphen;stranded polynucleotides. Formulas are derived which relate the stacking free energy and ring closure index to the maximum slope of the helix to coil transition in matching and dAT:dAT polynucleotides. The effect of interhyphen; and intrastrand excluded volumes on transition point and on the stacking free energy in double stranded molecules has been examined. Both excluded volume effects have been expressed by a single parameter ggr;, which appears in the relation between the mean square endhyphen;tohyphen;end distance and the number of units in a given polymer. It is concluded that the interstrand excluded volume effect shifts the transition point, descreases the tgr; value, and increases the egr; value for doublehyphen;stranded molecules.
展开▼
