On the flexibility of the boundaries between the A-form and B-form sections in DNA molecule.
The degree of orientation of DNA in a flow has been studied within the interval of the B - A transition induced by ethanol. The orientation of the B DNA (60-65% ethanol, v/v) and that of the A DNA (80-82% ethanol) are nearly identical. This means that both conformations have similar persistence lengths and that there is no aggregation in the course of formation of the A form. Within the transition range (65-78% ethanol) the orientation attains a sharp minimum which coincides with the half-transition point (73% ethanol). The cooperative character of the B - A transition presupposes the existence of boundaries between the alternating sections of the A and B conformations that may entail an increased flexibility of the DNA molecule and a corresponding drop of orientation. Theory predicts an elliptical dependence of the number of boundaries on the proportion of the A form. The experimental degree of orientation follows the same pattern. Quantitative evaluation shows that the flexibility of a boundary is small, so that several dozen of boundaries are required to simulate free rotation.
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004247:DNA; D000431:Ethanol; D006860:Hydrogen Bonding; D008956:Models, Chemical; D009690:Nucleic Acid Conformation; D012212:Rheology; D012996:Solutions; D014867:Water
D012996:Solutions; D014867:Water; D000431:Ethanol; D004247:DNA