Why is the Tm of DNA higher with GC ratioSolutionTm is defin

Why is the Tm of DNA higher with GC ratio?

Solution

Tm is defined as the temperature at which DNA strand denatures. Denaturation of DNA by definition is the separation of double stranded DNA into 2 single strands. In a double stranded DNA molecule, the both strands are connected to each other by the hydrogen bonds between the purines and pyramidines of the nucleotide base pairs. Adenine and Thymine are connected by a double Hydrogen bond. Whereas, Guanine and Cytosine are connected by triple hydrogen bond. High temperature breaks the hydrogen bonds and separates the strands. If a DNA fragment is rich in G C pairs, then it would be difficult to denature it and it needs higher temperature to break the triple hydrogen bonds between G and C compared to the douible hydrogen bonds between A and T. Hence the Tm is higher.