Question

you are given two solutions containning different purified DNAs. one is from the bacterium P. aeruginosa and has a G+C content of 68%, whereas other is from a mammal and has a G+ C content of 42.5%. which solution has the higher Tm value and why?

Answer 1

G and C binds with three hydrogen bonds. A and T binds with two hydrogen bonds. The amount energy which is required to breack three bonds needs more energy than the two hydrogen bonds.

If you take the frist DNA, the GC% is 68% which means the AT% = 32 (100-38).

If you take the second DNA the GC% is 42.8% which means the AT% = 57.2 (100-42.8).

The number of triple bonds is more with GC content, as the DNA with 68% has more number of triple bonds it requires more amount of energy to melt. So, the Tm is higher in 68%GC of DNA when compared with 42.5% GC DNA.