DNA is a charged semiflexible polymer. Apart from its fundamental importance for biology, codified mainly in the linear sequence of nucleotide bases along its length, it has many other fascinating properties that are mostly not related to its base sequence. It is these properties that are the focus of the physics of DNA. The most important physical properties of DNA are interactions and conformations. We have been studying both of them extensively.

The figure represents concentrated DNA in the s.c. line hexatic phase where one can study the interactions between very long DNA fragments (left). Though locally DNA is hexagonally packed it can make very complicated spatial structures where it has to wind back on itself because of volume constraints, like in this spherulite of a cholesteric phase in solution (right). Similar ordered structures exist also in several viruses.

There are several important physical problems that we have addressed recently:

DNA-DNA interactions. Segments of DNA molecule interact via electrostatic (at larger separations) and hydration (at smaller separation) forces. Both have been quantified in various ionic environments.

H.H. Strey, R. Podgornik, D.C. Rau and V.A. Parsegian: DNA-DNA Interactions, Curr. Opin. Struc. Biol. 8 (1998) 309-313.

DNA phase diagram. DNA in solutions makes a wide variety of ordered liquid crystalline mesophases that can be characterized by the type and range of molecular order. In the regime of DNA densities relevant for e.g. viral packing DNA is in a s.c. line hexatic phase.

R. Podgornik, H.H. Strey and V.A. Parsegian: Colloidal DNA, Curr. Opin. Coll. & Interf. Sci. 3 (1998) 534-539.

DNA elasticity. At very long length scales DNA behaves as a macroscopic elastic filament (an Euler - Kirchhoffian elastic filament). Elastic properties of this filament are codified by its bending and stretching moduli that depend essentailly on the interactions between DNA segments.

R. Podgornik, P.L. Hansen and V.A. Parsegian, Elastic moduli renormalization in self-interacting stretchable polyelectrolytes. J.Chem. phys., 2000, 113, pages 9343-9350 (1999)

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