1,721,592 research outputs found
The soft-mode instability of a membrane induced by strong polymer adsorption
No full textThe interaction between a flexible polymer and a fluctuating membrane is a fundamental problem in soft-matter physics with relevance to biological phenomena occurring in cells. We find that polymer fluctuations in a strongly adsorbed state can renormalize the bending rigidity of a planar membrane to a negative value. It gives rise to a novel phenomenon that the membrane with a small surface tension can be unstable to spontaneous formation of a soft mode, i.e., a large-amplitude undulation with the wavelength comparable to the interaction range which can be long.X113sciescopu
Effects of nonequilibrium fluctuations on ionic transport through biomembranes
No full textWe investigate the effects of nonequilibrium flutuations on ionic transport through ion channels in membranes using the concept of localized ratchet. Due to the localization, the ionic population in the binding site can be enhanced or suppressed depending upon ionic potential and its fluctuations, affecting the gating kinetics of the channel. The localized dichotomic fluctuations of ionic potential are shown to give rise to a current reversal differing from the results of periodic ratchets. It is also found that strong correlations between binding energy and membrane potential fluctuations induce resonancelike behaviors in ionic current as the fluctuating rate varies. [S1063-651X(99)17010-7].open1111sciescopu
Enhanced bubble formation in looped short double-stranded DNA
No full textRecent experiments have shown the double-stranded (ds) DNAs readily bend and loop over the scale much shorter than their persistence length (50 nm). In an effort to unveil this seemingly surprising phenomenon, we study the emergence of bubbles in short ds DNA loops by simulating the breathing DNA model. We analyze the bubble size distributions and the melting curves for varying contour lengths, which are critically compared with those of linear DNA of the same lengths. We analytically evaluate the free energies associated with double-strand bending and single-strand bubble formation to explain the simulation data. It is found that in shorter looped DNA the bubbles are more easily initiated and formed to release the large bending energy, giving rise to melting at a lower temperature and a lower contour length.open1144sciescopu
Does stochastic resonance occur in periodic potentials?
No full textThe possibility of observing stochastic resonance (SR) in a periodic potential without a static bias, driven by noise and an oscillating field, is investigated in both limits of damping. It is shown from the matrix continued fraction method that, although an underdamped Brownian particle moving in a periodic potential displays a dynamical resonance facilitated by noise, there is no conventional SR irrespective of damping. The reason such SR cannot be observed in an overdamped regime is demonstrated by a hopping model. Due to the unbound motion in the periodic potential, transition probability decays algebraically and there is no persistent synchronized hopping. However, the noise-induced enhancement of the diffusion constant related to escape rate enhancement exhibits an SR-like behavior. A comparison with the dynamics on a circle as a different example of an unbound system is given.open1127sciescopu
Charge density and bending rigidity of a rodlike polyelectrolyte: Effects of multivalent counterions
No full textWe study line charge density and bending persistence length of a semiflexible polyelectrolyte rod typified by DNA in a z:1 electrolyte with or without pre-existing 1:1 salt. We use a wormlike chain model, where the effective Hamiltonian incorporates bending energy, as well as where the Coulomb interaction between charged segments is screened and mediated by the ions in the solution. By analytically evaluating the free energy associated with the contour undulation and charge density fluctuation affected by the adsorbed ions, we find renormalized mean line-charge-density and persistence length. Multivalent counterions bind to the polyelectrolyte more readily than monovalent counterions, due to electrostatic attraction dominant over the entropy. Also, our results show that at physiological conditions the electrostatic interaction gives no appreciable change on the persistence length from its bare value, against the implications of earlier studies. This is because the mean-field and charge fluctuation effects largely cancel each other in the rodlike conformation.open1177sciescopu
Polymer translocation induced by adsorption
No full textWe study the translocation of a flexible polymer through a pore in a membrane induced by its adsorption on the trans side of the membrane. When temperature T is higher than T-c, the adsorption-desorption transition temperature, the attractive interaction between polymer and membrane plays little role in affecting polymer conformation, leading to translocation time that scales as tau similar to L-3, where L is the polymer contour length. When T<T-c, however, the translocation time undergoes a sharp crossover to tau similar to L-2 for sufficiently long polymers, following the second-order conformational (adsorption) transition. The translocation time is found to exhibit the crossover around T=T-c', which is lower than T-c for polymers shorter than a critical length (N < N-c). (C) 1998 American Institute of Physics.open11100sciescopu
Vesicular budding induced by a long and flexible polymer
No full textWe investigate the shape transformation of a vesicle incorporated with a long and flexible polymer. We evaluate the grand canonical partition function of the polymer to consider the effects of chain conformational changes on the membrane. It is found that the polymer loops with the ends adsorbed or anchored on the membrane play a major role on vesicular budding transition.X1118sciescopu
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