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Stepwise unfolding of collapsed polymers
D Marenduzzo1, A Maritan, A Rosa
1Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OX1 3NP, England, UK. davide@thphys.ox.ac.uk
The European Physical Journal. E, Soft Matter
|October 14, 2004
Summary
Recent studies on DNA stretching reveal that polymer chains unravel in steps due to surface effects. This phenomenon, observed in flexible and stiff polymers, explains peaks in characteristic curves during DNA stretching experiments.
Area of Science:
- Polymer physics
- Biophysics
- Statistical mechanics
Background:
- Recent experimental data show DNA stretching in the presence of polyvalent counterions.
- Understanding polymer chain unfolding is crucial for interpreting biophysical experiments.
Purpose of the Study:
- To investigate the force-induced unfolding of homopolymers on and off lattices.
- To explain the emergence of peaks in characteristic curves during DNA stretching experiments.
Main Methods:
- Studied polymer unfolding in a fixed force ensemble.
- Performed approximate analytical and numerical calculations in a quasi-equilibrium fixed stretch ensemble.
- Analyzed the impact of surface effects and initial polymer configuration (spool) on unfolding.
Main Results:
- In the fixed force ensemble, polymer globules unravel in steps due to surface effects, significant for finite-size chains.
- Both flexible and stiff polymers exhibit step-wise unraveling.
- In a fixed stretch ensemble, average force versus elongation curves display peaks related to the initial spool-like configuration.
Conclusions:
- Surface effects play a key role in the step-wise unfolding of finite polymer chains.
- The geometry of the initial polymer configuration can lead to peaks in force-elongation curves.
- The proposed mechanisms may couple in experiments, with dynamic effects also contributing.