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DNA Topoisomerases

DNA Topoisomerases

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. Type I...

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Tethered DNA dynamics in shear flow.

Yu Zhang¹, Aleksandar Donev, Todd Weisgraber

¹Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706-1691, USA.

The Journal of Chemical Physics

|June 25, 2009

Summary

This summary is machine-generated.

This study investigates polymer dynamics in shear flow, suggesting a standard stochastic process rather than previously claimed cyclic periodicity. Findings challenge existing theories on polymer behavior under flow conditions.

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Area of Science:

Polymer physics
Fluid dynamics
Computational physics

Background:

Understanding polymer behavior in shear flow is crucial for materials science and biophysics.
Previous studies suggested cyclic dynamics for tethered polymers, but experimental and simulation evidence remains debated.

Purpose of the Study:

To investigate the cyclic dynamics of a single polymer tethered to a hard wall in shear flow.
To examine the influence of chain length (N) and dimensionless shear rate (Wi) on polymer dynamics.
To clarify the nature of polymer motion, specifically questioning previously claimed periodicity.

Main Methods:

Utilizing Brownian dynamics, the lattice Boltzmann method, and stochastic event-driven molecular dynamics simulations.
Focusing on the dynamics of the free end (last bead) of the tethered polymer chain.
Analyzing cross-correlation functions and power spectral densities of chain extensions in flow and gradient directions.

Main Results:

Extensive simulation results indicate a classical fluctuation-dissipation stochastic process.
Evidence suggests that the cyclic dynamics of the polymer chain may not be periodic as previously claimed.
Analytical calculations for a harmonic dimer in shear flow support the numerical findings.

Conclusions:

The dynamics of a single tethered polymer in shear flow are best described by a fluctuation-dissipation stochastic process.
The existence of periodicity in cyclic dynamics is questioned, challenging prior research.
This work provides a more accurate understanding of polymer behavior under shear flow conditions.