HYDRODYNAMICS OF A DNA MOLECULE IN A FLOW-FIELD

The hydrodynamics of a single, fluorescing, DNA molecule held at one e nd by ''optical tweezers'' and subjected to a uniform flow are compare d with Monte Carlo simulations that account for the molecule's entropi c elasticity, Brownian motion, and hydrodynamic drag. Using self-diffu sion data and analytic expressions to obtain the drag in the limits of the undeformed coil and of the fully stretched thread, the predicted chain stretching and mass distribution are in quantitative agreement w ith measurements. The results explain the success of the nonlinear ela stic ''dumbbell'' model in predicting the rheological properties of di lute polymer solutions.