Biomedical subjects

Tanniemola B Liverpool

Publications and source records attributed to Tanniemola B Liverpool.

8 recordsLinked to original sources

PubMed2006

Active gels: where polymer physics meets cytoskeletal dynamics.

The cytoskeleton provides eukaryotic cells with mechanical support and helps them to perform their biological functions. It is predominantly composed of a network of semiflexible polar protein filaments. In addition, there are many accessory proteins that bind to these filaments, regulate their assembly, link them to organelles and provide the motors that either move the organelles along the filaments or move the filaments themselves. A natural approach to such a multiple particle system is the study of its collective excitations. I review some recent work on the theoretical description of the emergence of a number of particular collective motile behaviours from the interactions between different elements of the cytoskeleton. In order to do this, close analogies have been made to the study of driven soft condensed matter systems. However, it emerges naturally that a description of these soft active motile systems gives rise to new types of collective phenomena not seen in conventional soft systems. I discuss the implications of these results and perspectives for the future.

Actins↗

PubMed2006

Condensation of DNA-actin polyelectrolyte mixtures driven by ions of different valences.

Multivalent ions can induce condensation of like-charged polyelectrolytes into compact states, a process that requires different ion valences for different polyelectrolyte species. In this work we examine the condensation behavior in binary anionic polyelectrolyte mixtures consisting of DNA coils and F-actin rods in the presence of monovalent, divalent, and trivalent ions. As expected, monovalent ions do not condense either component and divalent ions selectively condense F-actin rods out of the polyelectrolyte mixture. For trivalent ions, however, we observe a microphase separation between the two polyelectrolytes into coexisting finite-sized F-actin bundles and DNA toroids. Further, by increasing the DNA volume fraction in the mixture, condensed F-actin bundles can be completely destabilized, leading to only DNA condensation within the mixture. We examine a number of possible causes and propose a model based on polyelectrolyte competition for ions.

Actins↗

PubMed2005

Dynamics of inextensible semiflexible filaments.

We address the problem of the fluctuating dynamics of an isolated inextensible and semiflexible filament of length L . By focusing explicitly on two key properties of the filaments--their connectivity and inextensibility--we obtain insights into their dynamics. We calculate the dynamics, and we calculate the correlation functions for chains of finite length taking into account the boundary conditions at the chain ends. We obtain closed-form expressions that separate the internal bending modes from the global rotation modes.

Journal Article↗

PubMed2005

Propulsion of a molecular machine by asymmetric distribution of reaction products.

A simple model for the reaction-driven propulsion of a small device is proposed as a model for (part of) a molecular machine in aqueous media. The motion of the device is driven by an asymmetric distribution of reaction products. The propulsive velocity of the device is calculated as well as the scale of the velocity fluctuations. The effects of hydrodynamic flow as well as a number of different scenarios for the kinetics of the reaction are addressed.

Colloids↗

PubMed2004

Statistical mechanics of double-helical polymers.

We introduce a simple geometric model for a double-stranded and double-helical polymer. We study the statistical mechanics of such polymers using both analytical techniques and simulations. Our model has a single energy scale which determines both the bending and twisting rigidity of the polymer. The helix melts at a particular temperature T(c) below which the chain has a helical structure and above which this structure is disordered. Under extension we find that for small forces, the behavior is very similar to wormlike chain behavior but becomes very different at higher forces.

Biopolymers↗

PubMed2003

Instabilities of isotropic solutions of active polar filaments.

We study the dynamics of an isotropic solution of polar filaments coupled by molecular motors which generate relative motion of the filaments in two and three dimensions. We investigate the stability of the homogeneous state for constant motor concentration taking into account excluded volume and an estimate of entanglement. At low filament density the system develops a density instability, while at high density entanglement drives the instability of orientational fluctuations.

Actins↗

PubMed2003

Anomalous fluctuations of active polar filaments.

Using a simple model, we study the fluctuating dynamics of inextensible, semiflexible polar filaments interacting with active and directed force generating centers such as molecular motors. Taking into account the fact that the activity occurs on time scales comparable to the filament relaxation time, we obtain some unexpected differences between both the steady-state and dynamical behaviors of active as compared to passive filaments. For the statics, the filaments have a length-scale-dependent rigidity. Dynamically, we find strongly enhanced anomalous diffusion.

Actin Cytoskeleton↗

PubMed2002

Conformational instability of rodlike polyelectrolytes due to counterion fluctuations.

The effective elasticity of highly charged stiff polyelectrolytes is studied in the presence of counterions, with and without added salt. The rigid polymer conformations may become unstable due to an effective attraction induced by counterion density fluctuations. Instabilities at the longest, or intermediate length scales, may signal collapse to globule, or necklace states, respectively. In the presence of added salt, a generalized electrostatic persistence length is obtained, which has a nontrivial dependence on the Debye screening length. It is also found that the onset of conformational instability is a reentrant phenomenon as a function of polyelectrolyte length for the unscreened case, and the Debye length or salt concentration for the screened case. This may be relevant in understanding the experimentally observed reentrant condensation of DNA.

Journal Article↗