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Rotational drag on DNA: a single molecule experiment
Philippe Thomen1, Ulrich Bockelmann, François Heslot
1Laboratoire de Physique de la Matière Condensée, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France.
Physical Review Letters
|June 13, 2002
Summary
We studied rotational drag on DNA molecules by measuring forces during unzipping. Rotational friction torque increases with DNA length and cranking speed, impacting opening force.
Area of Science:
- Biophysics
- Molecular Biology
- Physical Chemistry
Background:
- Understanding DNA mechanics is crucial for molecular biology.
- Rotational dynamics of DNA influence its function and interactions.
- Previous studies have not fully quantified rotational drag effects on DNA unzipping.
Purpose of the Study:
- To investigate the impact of rotational drag on double-stranded DNA during mechanical unzipping.
- To quantify the relationship between rotational friction torque and DNA length and angular velocity.
- To estimate the magnitude of rotational torque for a specific DNA length and rotation rate.
Main Methods:
- Utilized a single-molecule configuration to study DNA mechanics.
- Measured forces during the mechanical opening (unzipping) and closing of the DNA double helix.
- Cranked one end of the DNA molecule while the other end was free to rotate.
Main Results:
- Rotational drag contributes an additional force during DNA double helix opening.
- The effect of rotational drag increases with the length of the DNA molecule.
- Rotational drag is approximately proportional to the angular velocity of cranking.
Conclusions:
- Rotational friction torque is a significant factor in DNA mechanical manipulation.
- An estimated torque of ~1k(B)T was observed for 10,000 base pairs of DNA at 2000 turns/sec.
- These findings provide insights into the physical properties of DNA under torsional stress.