High Quality Content by WIKIPEDIA articles! Nucleic acid thermodynamics is the study of the thermodynamics of nucleic acid molecules, or how temperature affects nucleic acid structure. For multiple copies of DNA molecules, the melting temperature (Tm) is defined as the temperature at which half of the DNA strands are in the double-helical state and half are in the "random-coil" states. The melting temperature depends on both the length of the molecule, and the specific nucleotide sequence composition of that molecule.