| Abstract: | The melting curve for a covalently closed circular DNA has been analyzed on the basis of an expression for the supercoiling energy derived in terms of the elastic parameters of the macromolecule, treated as a homopolymer. The result obtained by applying the usual methods of statistical mechanics indicate close agreement with the available experimental data. It is found that the elevation of the melting temperature, as compared to that of the nicked circular or linear DNA, is a natural consequence of the fact that the supercoiled molecule is constrained by an invariant linking number. The flattening of the melting curve, on the other hand, arises as the closed circular duplex melts into a loose helix rather than random coils. |
