Related Experiment Video
Updated: May 2, 2026
11:41
Magnetic Tweezers for the Measurement of Twist and Torque
Published on: May 19, 2014
25.2K
Torque transfer coefficient in DNA under torsional stress.
1UPR9080 CNRS, Université Paris Diderot, Sorbonne Paris Cité, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, Paris 75005, France. alexey@ibpc.fr
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 26, 2012
Summary
Researchers found that not all applied torque transfers to supercoiled DNA. A torque transfer coefficient (TTC) less than 1 should be assumed for accurate DNA mechanics interpretation.
Area of Science:
- Biophysics
- Molecular Biology
- Nanotechnology
Background:
- Nanotechniques enable single-molecule manipulation of supercoiled DNA.
- Accurate interpretation of DNA mechanics requires precise torque measurements.
Purpose of the Study:
- To investigate the relationship between external torques and internal twisting stress in DNA.
- To determine the torque transfer coefficient (TTC) in manipulated DNA molecules.
Main Methods:
- All-atom molecular dynamics (MD) simulations were employed.
- Analysis of torque transfer during DNA stretching and twisting experiments.
Main Results:
- A torque transfer coefficient (TTC) consistently less than 1 was observed.
- MD simulations indicate TTC values around 0.8 under optimal conditions.
- Achieving higher TTC values necessitates specialized experimental conditions.
Conclusions:
- External torques are not fully transferred to DNA's double helix twisting stress.
- The TTC is a crucial factor for accurate DNA mechanics interpretation.
- Discrepancies in measured DNA twisting rigidity may be attributed to the TTC.
Related Concept Videos
02:02DNA Topoisomerases
32.3K
Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. ...
Types and Mechanism of action
Topoisomerases are divided into two main types. ...
32.3K
01:18Stresses in a Shaft
1.2K
The shaft PQ is subjected to a twisting force when equal and opposite torques are applied on either side. A section that cuts perpendicular to the shaft's axis at any arbitrary point R is examined to understand this. When the free-body diagram of the QR segment is analyzed, it reveals the shearing forces exerted by the PR portion onto the QR segment as the shaft experiences twisting.
Applying equilibrium conditions to the QR segment establishes that the internal shearing forces within the...
Applying equilibrium conditions to the QR segment establishes that the internal shearing forces within the...
1.2K
01:18Stress Concentrations in Circular Shafts
739
Consider the elastic torsion formula, which applies to a circular shaft with a consistent cross-section. This formula assumes that the shaft's ends are loaded with rigid plates firmly attached. However, in many cases, torques are applied to the shaft through mechanisms like flange couplings or gears, which are connected by keys inserted into keyways. This application method modifies the stress distribution near the point of torque application, causing it to deviate from the distributions...
739
01:16Torsion of Noncircular Members
901
Circular shafts undergoing torsional stress maintain their cross-sectional integrity due to their axisymmetric nature. This symmetry ensures an even distribution of stress, allowing the shaft to withstand torsion without distorting. In contrast, square bars, lacking this axial symmetry, experience significant distortion across their cross-sections when subjected to torsion, with the exception of along their diagonals and at lines connecting midpoints. A detailed examination of a cubic element...
901
01:15Thin-Walled Hollow Shafts
740
In analyzing a thin-walled hollow shaft subjected to torsional loading, a segment with width dx is isolated for examination. Despite its equilibrium state, this segment faces torsional shearing forces at its ends. These forces are quantitatively described by the product of the longitudinal shearing stress on the segment's minor surface and the area of this surface, leading to the concept of shear flow. This shear flow is consistent throughout the structure, indicating a uniform distribution of...
740
01:15Design of Transmission Shafts - Stress Analysis
811
Designing a transmission shaft requires a thorough understanding of the stresses induced by bending moments and torques, especially in systems where power is transferred through gears. These forces create force-couple systems at the centers of the shaft's cross-sections, leading to both transverse and torsional loading. Although shearing stresses from transverse loads are typically smaller than those from torques and are often overlooked, the significant normal stresses from these loads...
811