Melting temperature

Encyclopedia : M : ME : MEL : Melting temperature

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The dissociation of a DNA double helix is often referred to as melting because it occurs quickly once a certain temperature has been reached. The melting temperature (T_m) is defined as the temperature at which 50% of the DNA molecules form a stable double helix and the other 50% have been separated to single strand molecules.

Methods

Various formulas with different accuracies are used to calculate T_m values Breslauer, K.J. et al. (1986) Proc. Natl. Acad. Sci. USA. 83: 3746-3750. [(pdf)] Rychlik, W. et al. (1990) Nucleic Acids Res. 18: 6409-6412. .

Wallace method

Suitable for oligos less than 18mers in length by counting the frequency of each nucleotide base.

[T_m = 2(A+T) + 4(G+C)]

The determination of T_m for DNA extracted from organisms was originally designed to determine the GC content of the DNA using the UV absorbance profile as a function of temperature. Mandel, M. and J. Marmur (1968) Methods in Enzymology 12 Nucleic Acids B: 195-206. For long chain DNA polymers CsCl density gradient analysis Meselson, M. F. W. Stahl and J. Vinograd (1957) Proc. Natl. Acad. Sci. USA. 43: 581-588 yields values which correlate with the melting temperatures Mandel, M. C. Schildkraut and J. Marmur (1968) Methods in Enzymology 12 Nucleic Acids B: 184-195. Where failures to correlate the buoyant density and the melting temperature arise (as in many bacteriophage DNAs) unusual bases have been found replacing all or part of one of the nucleotides in the genome.

References

See also

• denaturation (biochemistry)
• hybridisation
• PCR
• Melting point
• Primer for calculations of Tm

External links

• [T_m calculation] - by bioPHP.org.
• http://www.promega.com/biomath/calc11.htm#disc
• [Invitrogen T_m calculation]
• [AnnHyb software for T_m calculation using the Nearest-neighbour method]

 

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