DIRECT MEASUREMENT OF THE TRANSPORT-PROPERTIES OF A SINGLE DNA MOLECULE

A fluorescently labeled DNA molecule is end tethered to a small magnet ic bead and pulled by a calibrated magnetic force through a solution o f unlabeled DNA molecules to monitor the transport coefficients of the chain. From the force velocity diagram F-V, we report the first direc t measurement of the friction coefficient zeta = F/V of a single DNA m olecule. zeta is found to be highly velocity dependent due to sharp co nformational transitions for increasing velocities in agreement with a recent model by Ajdari et al.