Condensed Matter Physics Seminar

Ideal polymers: equilibrium properties from non-equilibrium processes, Raz Halifa-Levi , TAU

Abstract:

I consider several cases of an ideal polymer being dragged by an external force. The work W in such a process depends on the initial state of the polymer, and it's distribution can be related to the difference in the free energy ∆F between the initial and the (equilibrated) final states by the means of Jarzynski equality. I consider both Newtonian and over-damped Langevin dynamics, for a polymer moving in a free space or initially located near a repulsive wall. I reconstruct (either analytically or numerically) the distribution of W, and demonstrate that there is critical velocity vc such that for v<vc  the ∆F can be easily reconstructed, while for v>>vc  such reconstruction is, practically, impossible. The velocity vc  depends on the number of monomers and other parameters of the problem.

Axial symmetric lipid membrane under external pressure - a model system for fission of mitochondria mediated by the endoplasmic reticulum, Gonen Golani, TAU

Abstract:

Fission of mitochondria mediated by ER occurs at the point of contact between the two, consists of two stages, and is facilitated mainly by DNM1 protein and actin filaments. In the first stage, ER tubules warp the mitochondrial membrane and actin filaments associated with the ER generate pressure on the mitochondrial membrane causing narrowing of the mitochondria diameter. The second stage occurs when the radius of the mitochondria at the ER-mitochondria junction is reduced to about 40% of its initial value. At this point, the DNM1 self-assembles on the mitochondria membrane and facilitates fission by an unknown mechanism.

In this work we present a physical mechanism of the mitochondrial constriction necessary for the onset of DNM1 action. We consider two versions of such mechanism– in the first the actin filaments that originate from the ER tube polymerize and apply force on the outer membrane of the mitochondria, in the second the force is generated by myosin-II mediated contraction of actin filaments that wraps the mitochondria.

Seminar Organizer: Prof. Sasha Gerber