Light scattering study of natural DNAs over a wide range of molecular weights: Evidence for compaction of the large molecules

This work reports light scattering measurements on DNA in aqueous solutions (100 mM NaCl, 1 mM EDTA and 10 mM Tris-HCl buffer, pH 7.8) over a wide range of molecular weights (102-105 base pairs) and shows that, in the above standard solvent, shorter chains (<104 base pairs) behave as a “wormlike chain” and their diffusion coefficients as obtained by dynamic light scattering measurements, confirm the prediction of standard wormlike model, whilst longer chains (>104 base pairs) behave in a different manner. Dynamic and static light scattering and SEM analysis indicate that DNA molecules 105 base pairs long, condense into compact structures in our solvent conditions. Calculations done using a wormlike model are also presented and discussed in comparison both to our experimental data and to other data reported in the literature.