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Updated: Jun 20, 2026

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers
Published on: October 13, 2011
Compaction and swelling of single stretched DNAs driven by molecular crowding
Paritosh Gupta1, John F Marko2, Vittore F Scolari3
1Indian Institute of Science Education and Research, CNRS, Sorbonne Université, PSL, Institut Curie, CNRS, Sorbonne Université, PSL, Institut Curie, Physique des Cellules et Cancer, Research University, UMR168, Paris 75005, France; Laboratoire Dynamique du Noyau, Research University, UMR3664, Paris 75005, France; and Department of Physics, Dr. Homi Bhabha Road, Pune 411 008, India.
None:
We present a theory for the effects of osmotic pressure exerted by macromolecular crowders on a double-stranded DNA or other semiflexible polymer extended by tension. Our results predict the force and crowder-density dependence of the polymer extension. The lowest-order effect is a crowder-dependent compression that counteracts the external stretching force, which can collapse the polymer at a crowder-dependent critical force f^{*}. This compression is dependent on crowder radius r and density ϕ, with higher densities and smaller radii having greater effects on the force-extension curve. At first order in perturbation theory, we also find a fluctuation-dependent correction to the depletion volume, which can overwhelm the simple compression effect for large crowders, leading to expansion of the polymer.
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