Excluded volume effects in gene stretching

We investigate the effects excluded volume on the stretching of a single DNA in solution. We find that for small force F, the extension h is not linear in F but proportion to F(gamma), with gamma = (1 - nu)/nu, where nu is the well-known universal correlation length exponent. A freely joint chain model with the segment length chosen to reproduce the small extension behavior gives excellent fit to the experimental data of lambda-phage DNA over the whole experimental range. We show that excluded volume effects are stronger in two dimensions and derive results in two dimensions that are different from the three-dimensional results. This suggests experiments to be performed in these lower dimensions.