formamide for DNA

Todd Johnson TJOHNSON at
Fri Jun 16 12:08:26 EST 1995

A question was raised about the addition of formamide and its
specific function in DNA experimentation.

Formamide H2NCH=O is able to effectively compete for hydrogen bonding
locations on the different DNA bases.  Thus, the normal interactions
that hold the DNA duplex together (H-bonds) are broken and the
effective melting temperature of the DNA is lowered.  The actual
melting temperature (Tm) of complimentary DNA strands is directly
related to the formamide concentration (Tm= 81.5 + (41 x GC pairs)
+ (16.6 x log [molarity of monovalent salt]) - (0.72 x % (v:v)

It is believed that urea reacts in the same manner.

Best wishes


Todd M. Johnson, Ph.D.
Chemistry Dept.
Weber State University

E-mail:  TJohnson at


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