LOW FREQUENCY DYNAMICS OF DNA

This dissertation describes an experimental study of the lowest lying vibrational modes of DNA. The importance of a dynamical understanding of this molecule is discussed, and the various theoretical approaches to DNA dynamics are reviewed. The lattice dynamical analysis of the "average" double helix and Lifshitz Green's Function analysis of local modes are considered in some detail. The application of inelastic laser light scattering as a probe of lattice and local modes is discussed.;The preparation and characterization (by gel electrophoresis and fiber diffraction) of oriented fibers of phenol extracted calf thymus DNA is described. Measurements of the zone center acoustic phonon shift yield the speed of sound both parallel to and perpendicular to the fiber axis. In B-DNA this is 1.89 (+OR-) 0.08 m/S, with no measurable anisotropy. In A-DNA the speed of sound perpendicular to the fiber axis is 2.22 (+OR-) 0.10 m/S with an increase of about 8% along the fiber axis in the most highly oriented samples. A wavevector independent mode is observed at about 580 MHz. This may be the predicted base destacking mode at a terminus. Initial searches for a soft optic mode in the range 0-20 cm('-1) were negative.