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Related Experiment Videos

Stretching DNA with optical tweezers

M D Wang1, H Yin, R Landick

  • 1Department of Molecular Biology, Princeton University, New Jersey 08544, USA.

Biophysical Journal
|March 1, 1997
PubMed
Summary

Researchers precisely measured DNA elasticity using optical trapping, finding that multivalent ions like Mg2+ significantly reduce DNA

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Polymer Physics

Background:

  • Understanding DNA mechanics is crucial for molecular biology.
  • Previous studies used various methods to measure DNA elasticity.
  • Optical trapping offers high-resolution force-extension measurements.

Purpose of the Study:

  • To accurately measure force-extension relationships of single DNA molecules.
  • To investigate the effect of buffer conditions and ionic strength on DNA elasticity.
  • To determine the persistence length and elastic modulus of DNA.

Main Methods:

  • Utilized a modified optical trapping interferometer with feedback control.
  • Attached one DNA end to a surface via stalled RNA polymerase.
  • Stretched DNA by moving a stage and recorded bead position with nanometer resolution.

Main Results:

  • Achieved rapid, accurate force-extension data for short DNA molecules (<1 micron).
  • Measured persistence length (Lp) of ~47 nm in 10 mM Na+ buffer.
  • Found Lp decreased to ~40 nm with multivalent cations (Mg2+, spermidine 3+).

Conclusions:

  • DNA's intrinsic persistence length is approximately 40 nm.
  • Multivalent ions significantly impact DNA's elastic properties.
  • Elasticity theories based on worm-like chain models accurately describe DNA stretching behavior.

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