Compaction and swelling of single stretched DNAs driven by molecular crowding

Area of Science:

• Biophysics
• Polymer Physics
• Statistical Mechanics

Background:

• Macromolecular crowders are used to study polymer behavior in crowded environments.
• Understanding polymer extension under tension is crucial in molecular biology and materials science.

Purpose of the Study:

• To develop a theory for the effects of osmotic pressure from macromolecular crowders on semiflexible polymers (like DNA) under tension.
• To predict how polymer extension depends on stretching force and crowder properties (density, size).

Main Methods:

• Theoretical modeling using perturbation theory.
• Analysis of osmotic pressure effects on polymer elasticity.

Main Results:

• Crowders induce a force-dependent compression, counteracting the stretching force.
• A critical force (f*) is predicted, at which the polymer may collapse.
• Crowder size and density influence the degree of compression.
• For large crowders, fluctuation effects can lead to polymer expansion, overriding compression.

Conclusions:

• Crowder-induced osmotic pressure significantly alters polymer force-extension behavior.
• The interplay between crowder size, density, and polymer tension dictates whether compression or expansion dominates.
• This theory provides insights into polymer physics in crowded biological and synthetic systems.