Polynucleotides helix-coil transition

Typical examples are the conversion of the neutral form of an amino acid into its zwitterionic form, the helix-coil transitions in polypeptides and polynucleotides, and other conformational changes in biopolymers. Reactions of higher molecularity in which reactants and products have different dipole moments are subject to the same effect (association of the carboxylic acids to form hydrogen-bonded dimers). Equilibrium involving ions are often more sensitive to the application of an electric field ... 

As discussed by Pdrschke one can distinguish several basic features of helix-coil transitions in polynucleotides. Formation of a helix from separated complementary... 

The successful application of high resolution nuclear magnetic resonance (NMR) spectroscopy to monitor the structure and dynamics of the helix-coil transition of oligonucleotide duplexes (1.-4) and transfer RNA (5—9) in solution have prompted efforts in our laboratory to extend these investigations to the polynucleotide duplex level in solution (10,11.). 

With the exception of helix/coil transitions of polypeptides and polynucleotides, the kinetics of conformational transitions has only been investigated to a slight extent. Relatively large rate constants of 10 -10 s" have been obtained for these helix/coil transitions. However, rate constants of 10" to 1 s have been obtained for denaturing processes where helix / coil transitions also play a role (see also Chapter 4.4.2). The high rates of helix / coil transitions are undoubtedly due to the cooperativity of the process. The low rates for denaturing must therefore result from nonhelical regions. 

J. R. Fresco and J. Massoulie Polynucleotides V. Helix-coil transition... 

Energetics of helix coil transitions in synthetic polynucleotides ... 

Fig. 6. The calculated standard Gibbs energy AG of the helix-coil transition of synthetic polynucleotide sequences (rf. Table 3) as a function of the sodium concentration [Na ] and the bulk sequence composition Xoc-...

Melting Temperature. The double helix of polynucleotides described above becomes thermodynamically unstable at particular temperatures (with specified conditions of solute concentration, pH, etc.) and is transformed into the open random-coil arrangement. This transformation is rather sharp, and can be measured by the concurrent changes in a number of physical properties of the nucleic acid, such as the optical absorption coefficient. The midpoint of the transition region is called the melting point. 

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