Multicomponent solutions of biological macro‐molecules: Thermodynamic and conformational studies of DNA

In this contribution we show how theoretical concepts and experimental procedures developed in the study of macromolecular solutions can be applied towards obtaining information on polymers of biological interest. Thermodynamic and conform ational studies of DNA solutions will be reviewed. Equilibrium sedimentation and density measurements under well specified conditions contribute to our understanding of preferential and, sometimes, specific interactions. Equilibrium sedimentation in a density gradient unambiguously determines the molecular weight of large DNA particles. The flexibility of DNA molecules is well described by the persistent, or worm‐like chain. The Kratky‐Porod persistence length (derived from light scattering and transport measurements) provides a unique parameter invariant over the whole molecular weight range accessible to experimentation. Angular dependence of the scattering of light has now been extended to the study of quasi‐elastic scattering which provides additional information with respect to internal motion and flexibility on DNA molecules.