[Heat-capacity of DNA at low temperatures and varying humidities].

Adiabatic low temperature microcalorimeter working in a wide temperature range, including that of liquid helium, is described. Heat capacity of DNA at various water concentrations was measured at 4-400 degrees K. It is shown that the pattern of its change is determined by the hydration parameter n (number of water molecules per mole of base pairs). According to the experimental findings the DNA molecule can be modelled by a sufficiently rigid "thin rod" and the dynamic characteristics of the subject under study can be explained in terms of monomeric continuum model. When studying low temperature heat capacity of DNA, account should be taken of the double helic hydration depending on GC-content. Measurement of heat capacity of DNA in native and denaturated states in a wide temperature range (4-400 degrees K) taking into account specific hydration of double helix allows a correct description of its thermodynamic properties.