I stand corrected. Thanks Darren.
I guess the definition of Tm can be a little fuzzy. For example, if I
take a solution of specific DNA (eg pBR322) and follow hypochromicity
(decrease in absorbance) as the temperature is gradually increased, I
will get a curve, the midpoint of which is the Tm. This midpoint will
be the same temperature no matter what my starting DNA concentration
is. Isn't that true? In other words, at a given temperature, a certain
fraction of the DNA is denatured. The reverse reaction of reannealing
the single strands is concentration dependent since the frequency of
collisions between DNA molecules will vary with concentration. But if
Tm is the temparature at which 50% of the DNA molecules have denatured,
is this concentration dependent?
Bob Gross
Dept. of Biology, Dartmouth College
bob.gross at dartmouth.edu
