Semiflexible polymers are widepread in living cells.
Examples are DNA, the carrier of our genetic material, and actin and microtubuli that are
making up the cytoskeloton of a cell.
Nowadays there are many micromanipulation experiments that allow to stetch, compress or twist such polymers.
Our goal is to find analytical models that allow to predict the outcome of such experiments. Often the arrangement
can be more complex than just stretching a naked chain. As indicated in the figure below a DNA chain can
feature a loop or kink (induced by a bound protein) or the boundary condition can be nontrivial.
(1) Through a semiclassical treatment we were able to obtain analytical expressions to describe such setups.
What we find is that the stiffness of the chain (characterized by the persistence length) appears to be smaller
for such a system. This allows e.g. to extract from such a measurement the angle that a protein induces
on the DNA chain (see b in the figure above).
(2) We studied also the buckling of a semiflexible chain under compression. Such a situation occurs when
e.g. a microtubule grows against a wall (M. E. Janson and M. Dogterom, Phys. Rev. Lett. 92, 248101
(2004)).
(3) Currently we are calculating the behavior of DNA under tension when a fixed number of turns is introduced
into the chain. Such experiments are now performed worldwide by using magnetic tweezers. In such a case
one finds the formation of supercoils. We are able to predict quantitatively this effect in an analytical model
without any adjustable parameters for a wide range of salt concentrations.
Check out some of our recent contributions:
I. M. Kulic, H. Mohrbach, V. Lobaskin, R. Thaokar and H.
Schiessel: Apparent persistence length renormalization of bent DNA
, Phys. Rev. E 72, 041905 (2005)
I. M. Kulic, H. Mohrbach, R. Thaokar and H. Schiessel, Equation of state
of looped DNA, Phys. Rev. E75, 011913 (2007)
M. Emanuel, H. Mohrbach, M. Sayar, H. Schiessel and I. M. Kulic: Buckling
of stiff polymers: Influence of thermal fluctuations, Phys. Rev. E76, 061907-1-13 (2007)
