Force-displacement relations at compression of dsDNA macromolecules

Area of Science:

• Computational Physics
• Biophysics
• Polymer Science

Background:

• Understanding the elastic properties of double-stranded DNA (dsDNA) is crucial for molecular biology and nanotechnology.
• Previous models have shown limitations in accurately describing dsDNA behavior, particularly under compressional forces.

Purpose of the Study:

• To investigate the elasticity of dsDNA molecules using Monte Carlo simulations.
• To evaluate different simulation ensembles (Gibbs and Helmholtz) for their accuracy in predicting force-displacement curves.
• To elucidate the shortcomings of existing models like the Marko-Siggia relation under specific force conditions.

Main Methods:

• Utilized Monte Carlo simulations with a coarse-grained model of DNA.
• Computed force-displacement (f-r) curves under constant force (Gibbs) and constant length (Helmholtz) ensembles.
• Focused analysis on compressional (negative) and weak tensile forces.

Main Results:

• Vector Gibbs ensemble simulations inaccurately represent polymer compression behavior.
• Scalar Gibbs protocol simulations show qualitatively correct dsDNA compression when using quadratic averages of displacements.
• The Marko-Siggia relation's limitations at weak tensile forces were identified.
• Constant length ensemble simulations and new closed-form expressions accurately depict dsDNA elasticity across a wide range of forces (negative and positive).

Conclusions:

• The constant length ensemble and novel closed-form expressions provide a realistic model for dsDNA elasticity.
• Simulation methods, particularly the choice of ensemble and averaging, significantly impact the accuracy of predicted dsDNA compression.
• Experimental setup specifics and averaging methods may greatly influence the observed elastic response of DNA molecules.