40 research outputs found
Interactions between proteins bound to biomembranes
We study a physical model for the interaction between general inclusions
bound to fluid membranes that possess finite tension, as well as the usual
bending rigidity. We are motivated by an interest in proteins bound to cell
membranes that apply forces to these membranes, due to either entropic or
direct chemical interactions. We find an exact analytic solution for the
repulsive interaction between two similar circularly symmetric inclusions. This
repulsion extends over length scales of order tens of nanometers, and contrasts
with the membrane-mediated contact attraction for similar inclusions on
tensionless membranes. For non circularly symmetric inclusions we study the
small, algebraically long-ranged, attractive contribution to the force that
arises. We discuss the relevance of our results to biological phenomena, such
as the budding of caveolae from cell membranes and the striations that are
observed on their coats.Comment: 22 pages, 2 figure
Public International Law: Environmental Law
Noteworthy international activity relating to the environment occurred in a wide variety of fora in 2000. This chapter provides brief updates on some of the most significant developments. Though by no means a comprehensive review, the chapter reflects the wide sweep of issues and large number of entities now involved in the development of international environmental law, at the start of this new century. It also reflects how critical and complex this international work is, and how much remains to be done
Dynamic phase separation of fluid membranes with rigid inclusions
Membrane shape fluctuations induce attractive interactions between rigid
inclusions. Previous analytical studies showed that the fluctuation-induced
pair interactions are rather small compared to thermal energies, but also that
multi-body interactions cannot be neglected. In this article, it is shown
numerically that shape fluctuations indeed lead to the dynamic separation of
the membrane into phases with different inclusion concentrations. The tendency
of lateral phase separation strongly increases with the inclusion size. Large
inclusions aggregate at very small inclusion concentrations and for relatively
small values of the inclusions' elastic modulus.Comment: 6 pages, 6 figure
The shape of polymer-decorated membranes
Flexible membranes with anchored polymers are studied using both analytical
methods and Monte Carlo simulations. The anchored polymers exert an
entropically induced pressure on the membrane which is calculated
explicitly using a small-gradient expansion. Likewise, we are able to
determine both the shape profile of the membrane, which approaches a cone-like
shape close to the anchor and a catenoid far away from it, and the profile of
the induced mean curvature. We also consider membranes decorated by many
polymers and identify two coverage regimes; one of which is governed by
polymer/membrane and the other by polymer/polymer interactions
Adsorption of polymers anchored to membranes.
Polymers, which are attached to a membrane at one of their ends, exert an
entropic pressure, which curves the membrane away from the
polymers. It is shown that adsorption which arises from a short-ranged
potential between the polymer and the membrane has a large influence on the
curvature of the membrane, leading to a decrease of the entropically induced
curvature. If one ignores the finite size of the anchor segment, the
polymer-induced curvature does not change sign and vanishes in the limit of
strong adsorption and a pure contact potential. If one includes the finite
size of the anchor segment, the membrane bends towards the polymer for
sufficiently strong adsorption