The Temperature of Melting (Tm) refers to the temperature at which 50% of double-stranded DNA (dsDNA) is changed to single-standard DNA (ssDNA). In the double helix of DNA, Adenine bases always pair with Thymine bases through two hydrogen bonds, whereas Guanine bases always pair with Cytosine bases through three hydrogen bonds. In consequence, a DNA molecule containing a higher GC content is more stable than another DNA molecule containing a lower GC content. The Tm can be calculated as follows = 2 °C(A + T) + 4 °C(G + C) = °C Tm (this equation is useful for oligonucleotides of 14 to 20 base-length).
