Belarusian State University, Belarus

Molecular DNA diagnostics being directed to detecting unknown point mutations such as single-nucleotide genomic variations, is based on temperature-dependent hybridization processes between target deoxyribonucleic acid molecules (target DNA) and probe DNA molecules. Due to the lack of a satisfactory theory of the helix–coil phase transition, phenomenological formulas for DNA melting temperature calculations are ordinary used in molecular genetic DNA studies. The difficulties of the phenomenological approach are stipulated by the increased noise in melting curves as the number of experimental points increases at decreasing the temperature discretization step. In this report, we propose a geometrodynamic approach to describing the helix–coil transition in double-stranded DNA (dsDNA) as a first-order phase transition at the interface between aqueous and dielectric media. One of the media is an aqueous salt solution (electrolyte). Due to the hydrophilicity of phosphate groups, one strand (ssDNA) of dsDNA is getting away into the aqueous medium as a temperature become above the melting point. In our model, the hydrophobic base pairs of dsDNA are located inside a cylinder with a diameter equal to that of the DNA helix. The dielectric interior of the cylinder, simulating dsDNA, is a medium near the boundary of which hydrophilic phosphate groups are located. In the coil transient DNA state, the hydrated phosphate groups form a Langmuir monolayer on the cylindrical surface. There exists an electrostatic potential at the interface. The phosphate groups leave the hydrated complexes under the action of the electrocapillary forces during the phase transition to double helix state and then, at the end of the phase transition, form an ordered monolayer. It is assumed that fluctuations in DNA result in the emergence of loops as domains (bubbles) of the new phase. We study the sensitivity of melting temperature to nucleotide composition and show that the two-dimensional phase transition is a true first-order phase transition without any spreading over the temperature scale.