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Melting point of double stranded DNA means the temperature at which the two strands separate by breakage of the Hydrogen bonds between the purine and pyrimidine bases. As G and C residues are joined by three Hydrogen bonds whereas A and T residues are joined by two Hydrogen bonds, the energy required to separate the strands of any DNA rich in G-C bases is more than that required to separate the strands of any A-T rich sequence. So, G-C content of the ds DNA is the most important factor for determining the melting temperature of DNA.



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More the number of hydrogen bonds, higher will be the melting point for a DNA (as higher energy will be required to break greater number of bonds). In a DNA, A joins with T via two hydrogen bonds while G joins with C via three hydrogen bonds. So clearly GC rich DNA will have more the number of hydrogen bonds as there are in AT rich DNA. Hence GC rich DNA will have higher melting point (Tm) as compared to AT rich DNA.

Hi Ram Mohan Nayak !

GC rich DNA has higher melting point. Because G-C pairs form three hydrogen bonds, while A-T pairs form only two, the higher the percentage of GC content, the higher its melting temperature. Thus, A double-stranded DNA rich in G and C needs more energy to be broken than one that is rich in A and T .

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