Statistical and Biological Physics

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Excluded volume effects on semiflexible ring polymers

Fabian Drube, Karen Alim, Guillaume Witz, Giovanni Dietler and Erwin Frey

poly_excl One aim of modern biotechnology is the controlled assembly and manipulation of structures. The simplest building blocks for constructing structures are rodlike polymers. The next higher level of complexity concerning building blocks is achieved with ringlike polymers. On the nano scale level the effective shape of such building blocks is governed by the interplay of entropic forces on the one hand and elastic stiffness and steric hindrance of the polymer segments on the other hand. Entropic forces lead to a coiled, cigar-like shape. This is opposed by elastic bending stiffness, which favors non-curved conformations. This poses the question how strong each of these molecular based forces contribute and how they affect the resulting shape of the building blocks.

We investigate the strength of entropic, steric and elastic forces on the shape of DNA rings on flat surfaces by experimental imaging and theory. Altogether we give a quantitative description of DNA rings, which enables a direct translation of molecular properties like bending stiffness and DNA diameter into nano scale properties like shape and size. We hope that our insights stimulate further development of nano structures.