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Watching molecules crowd: DNA double helices under osmotic stress
R Podgornik1, H H Strey, D C Rau
1Laboratory of Structural Biology/DCRT/NIDDK, National Institutes of Health, Bethesda, MD 20892, USA.
Biophysical Chemistry
|December 1, 1995
Summary
High concentrations of DNA cause molecules to straighten and become confined, driven by electrostatic repulsion, not just physical contact. This packing behavior is observed in liquid crystalline DNA phases under osmotic pressure.
Area of Science:
- Biophysics
- Materials Science
- Polymer Chemistry
Background:
- In dilute solutions, long DNA polyelectrolytes adopt random coil conformations.
- Understanding DNA packing at high concentrations is crucial for biological and material applications.
Purpose of the Study:
- To investigate the packing and energetics of high-density liquid crystalline DNA phases.
- To elucidate the mechanisms driving DNA molecule crowding and confinement at increasing concentrations.
Main Methods:
- Simultaneous measurements of DNA packing and energetics under osmotic stress.
- X-ray scattering to analyze structural and dynamic characteristics of ordered DNA phases.
- Direct measurement of packing energies and structural parameters.
Main Results:
- Increasing DNA concentration leads to straightening of random coils and molecular confinement.
- DNA molecules become progressively immobilized within 'cages' formed by neighbors.
- Confinement is dominated by soft potentials of electrostatic or hydration repulsion, not steric forces.
Conclusions:
- DNA crowding in liquid crystalline phases is driven by electrostatic/hydration repulsion, leading to molecular straightening and immobilization.
- Observed packing behavior deviates from models based solely on steric repulsion.
- Direct measurements confirm the role of intermolecular forces in confining DNA motion.