The DNA molecule can take various conformational forms. Investigations
focus mainly on the so-called ‘B-form’, schematically drawn in the famous
paper by Watson and Crick [1]. This is the usual form of DNA in a biological
environment and is the only form that is stable in an aqueous environment.
Other forms, however, can teach us much about DNA. They have the same
nucleotide base pairs for ‘building blocks’ as B-DNA, but with different
relative positions, and studying these forms gives insight into the interactions
between elements under conditions far from equilibrium in the B-form.
Studying the thermal denaturation is particularly interesting because it provides
a direct probe of those interactions which control the growth of the
fluctuations when the ‘melting’ temperature is approached. Here we report
such a study on the ‘A-form’ using calorimetry and neutron scattering. We
show that it can be carried further than a similar study on B-DNA, requiring
the improvement of thermodynamic models for DNA.
