[Thermodynamic models of binding ligands to nucleic acids]

Models of adsorption were considered, which describe the binding of biologically active ligands on DNA templates. The binding is described most comprehensively and in greatest detail by the distribution function, which determines the probability of detecting the preset number of adsorbed ligands on the template. In the case of noncooperative binding, this function corresponds to the Gaussian distribution and is characterized by two quantities: the mean value of the occupation of the template by ligands and the dispersion of occupation. The accuracy of the occupation of the template by ligands is inversely proportional to dispersion. As the length of the template and the number of reaction sites covered by one ligand upon binding increase, the accuracy of the occupation of the template by ligands increases. An important characteristic of binding is the degree of coverage of the template by ligands. This characteristic represents the portion of template reaction sites covered by all ligands adsorbed on the template. If polycations are bound to nucleic acid molecules, the coverage of the template determines the transition of nucleic acids to a compact state. The degree of template coverage for extended ligands depends only slightly on the binding constant in a wide range of concentrations of a free ligand in solution. Different adsorption models are considered from the unified point of view. The classification of cooperative interactions for a wide class of systems is given, from situations when several ligands are bound on nucleic acid templates to a situation when templates change by the action of ligands and begin to interact with each other.