Analysis of an experimental model of DNA unwinding.

Experiments are described, showing that DNA solutions with lithium chloride present a hypochromicity, which increases with the molarity of the salt. Different absorbancy versus temperature curves are obtained for different solutions, and it is found that the melting point (Tm) increases with the lithium chloride concentration. When cooling the samples, the absorbancy decreases in a symmetric way. In accordance with this model, a theory of DNA unwinding is proposed, assuming that before the unwinding, it is necessary a stretching of the molecule which eases this process. An extension of these ideas are applied, to the transcription DNA-RNA operation.