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Single-stranded nucleic acid elasticity arises from internal electrostatic tension.

David R Jacobson1, Dustin B McIntosh1, Mark J Stevens2

  • 1Department of Physics, University of California, Santa Barbara, CA 93106.

Proceedings of the National Academy of Sciences of the United States of America
|May 3, 2017
PubMed
Summary
This summary is machine-generated.

Flexible polyelectrolytes like single-stranded nucleic acids (ssNAs) have complex conformations. This study quantifies their elasticity in intermediate force regimes, revealing how salt concentration affects internal electrostatic tension.

Keywords:
electrostaticsflexible polyelectrolytesforce spectroscopysingle-stranded nucleic acids

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Area of Science:

  • Biophysics
  • Polymer Physics
  • Molecular Biology

Background:

  • Understanding flexible polyelectrolytes, such as single-stranded nucleic acids (ssNAs), is challenging due to the interplay between chain entropy and salt-dependent electrostatic forces.
  • Molecular elasticity measurements are crucial for probing polymer conformation, with existing studies elucidating ssNA behavior at low and high forces.

Purpose of the Study:

  • To investigate the elasticity of single-stranded DNA (ssDNA) and single-stranded RNA (ssRNA) in the intermediate-force regime (5-100 pN).
  • To develop and apply a modified wormlike chain model that incorporates internal electrostatic tension to explain ssNA elasticity.
  • To determine the relationship between salt concentration and internal electrostatic tension in ssNAs.

Main Methods:

  • Performed molecular elasticity measurements on ssDNA and ssRNA.
  • Applied a modified wormlike chain model incorporating internal electrostatic tension.
  • Analyzed elastic data across a range of ionic strengths (5 mM to 1 M).

Main Results:

  • ssNA elasticity was measured in the intermediate-force regime (50-85% extension).
  • The internal electrostatic tension decreased with increasing salt concentration, from approximately 5 pN at 5 mM to near zero at 1 M.
  • An analytical model of electrostatic screening quantitatively described this decrease, showing an effective charge density independent of force and salt.

Conclusions:

  • The study connects microscopic chain physics to macroscopic elasticity and structure for flexible polyelectrolytes.
  • A modified wormlike chain model with internal electrostatic tension accurately describes ssNA elasticity.
  • The findings provide a framework for understanding flexible polyelectrolyte behavior across various extensions and salt conditions.