Stretching of a single tethered polymer in a uniform flow.
The stretching of single, tethered DNA molecules by a flow was directly visualized with fluorescence microscopy. Molecules ranging in length (L) from 22 to 84 micrometers were held stationary against the flow by the optical trapping of a latex microsphere attached to one end. The fractional extension x/L is a universal function of eta vL 0.54 +/- 0.05, where eta and v are the viscosity and velocity of the flow, respectively. This relation shows that the DNA is not "free-draining" (that is, hydrodynamic coupling within the chain is not negligible) even near full extension (approximately 80 percent). This function has the same form over a long range as the fractional extension versus force applied at the ends of a worm-like chain. For small deformations (< 30 percent of full extension), the extension increases with velocity as x approximately v0.70 +/- 0.08. The relative size of fluctuations in extension decreases as sigma x/x approximately equal to 0.42 exp (-4.9 x/L). Video images of the fluctuating chain have a cone-like envelope and show a sharp increase in intensity at the free end.
Perkins
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Department of Physics, Stanford University, CA 94305, USA.
Smith
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Larson
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Chu
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D001704:Biopolymers / Q000737:chemistry; D004247:DNA / Q000737:chemistry / Q000648:ultrastructure*; D004548:Elasticity; D008856:Microscopy, Fluorescence; D008956:Models, Chemical; D009690:Nucleic Acid Conformation
D001704:Biopolymers; D004247:DNA