Physical approach of biological problems

Keywords: Statistical Physics, Non equilibrium phenomena, Membranes, Molecular motors, Cytoskeleton

Read the scientific activity report. (pdf 40Ko, last update 23th, april 2009)

A rapid inspection of orders of magnitude involved in cell components show that they are very similar to those relevant to “Soft Matter Physics”. There are however two important differences: biological systems are clearly out of equilibrium and molecular specificity can be strongly relevant. These simple remarks convince us that on the one hand Soft Matter Physics can provide a quantitative description of cellular systems, and that on the other hand biological systems raise an interesting number of new and challenging physical questions. For these reasons we concentrate our efforts towards understanding physical features of cell morphology and dynamics. This project is meaningful only with strong interactions with biologists.

Cells contain a very large number of components, but if we focus on mechanical properties, only a few classes of component are relevant: the cytoskeletal networks, molecular motors, phospholipid membranes and the large class of adhesion molecules such as integrins or cadherins. Therefore we study each of these components, keeping in mind the importance of the non-equilibrium behavior. In some cases, this requires the introduction of new physical concepts such as “active” membranes, “active” gels or  “isothermal ratchet”, which is a model to describe molecular motors by the Brownian motion of a particle switching between two different states.

A good physical understanding requires quantitative comparison between theory and experiments by systematically varying controlled parameters: for that reason, we work in close collaboration with the experimental groups both in our laboratory and in the Curie Subcellular structure and cellular dynamics Unit (UMR 144). For instance we contribute to the theoretical description of polymerization-based motion using biological models such as the bacteria Listeria and the keratocytes type of cells, but also biomimetic systems such as plastic beads and oil drops properly treated. Similarly we describe intra-cellular transport and interpret experiments on vesicles with the minimal numbers of components: Figure 1 shows a model of formation of membrane tubes by molecular motors and Figure 2 shows a model for the dynamin protein which is a protein involved in the breakage of membrane tubes.

Fig. 1

Fig. 2

We are convinced that we reached a reasonable physical understanding of each of the components and we extend our activity to the interaction between components. We are now able to discuss aspects of cell behavior such as cell motility, cell division and mechano-transduction. In the future, we will extend these studies to the multi-cellular level and study the mechanical properties of tissues. As an example, we show on Figure 3 the calculated beating pattern of a cilium such as those involved in the motion of a sperm cell, or of the protozoan paramecium.

Fig. 3 

Finally, many of these studies lead to the introduction of new physical concepts which are relevant to the general area of non-equilibrium physics: dynamic transitions, out of equilibrium fluctuations, active behavior...

Last update: April 2009

Last publications

2009

• Sorre B, Callan-Jones A, Manneville J, Nassoy P, Joanny JF, Prost J, Goud B, Bassereau P.
  Lipid Sorting In Membranes Nanotubes
  Biophysical Journal, 96(3):18a-19a
• G. Salbreux, J. Prost, J.-F. Joanny
  Hydrodynamics of Cellular Cortical Flows and the Formation of Contractile Rings
  Physical Review Letters, 103(5):058102 - Full version
• Prost J, Joanny JF, Parrondo JMR
  Generalized fluctuation-dissipation theorem for steady-state systems
  Physical Review Letters, 103(9): 090601
• Benoit Sorre, Andrew Callan-Jones, Jean-Baptiste Manneville, Pierre Nassoy, Jean-François Joanny, Jacques Prost, Bruno Goud, Patricia Bassereau
  Curvature-driven lipid sorting needs proximity to a demixing point and is aided by proteins
  Proceedings of the National Academy of Sciences of the United States of America, 106(14):5622-5626 - Full version
• O. Campàs, C. Leduc, P. Bassereau, J.-F. Joanny, J. Prost
  Collective Oscillations of Processive Molecular Motors
  Biophysical Reviews and Letters, 4(1-2):163-178 - Full version
• R. J. Hawkins, M. Piel, G. Faure-Andre, A. M. Lennon-Dumenil, J. F. Joanny, J. Prost, R. Voituriez
  Pushing off the Walls: A Mechanism of Cell Motility in Confinement
  Physical Review Letters, 102(5):058103 - Full version
• Jean-François Joanny, Jacques Prost
  Active gels as a description of the actin-myosin cytoskeleton
  HFSP Journal, 3(2):94-104 - Full version
• Padinhateeri Ranjith, David Lacoste, Kirone Mallick, Jean-François Joanny
  Nonequilibrium Self-Assembly of a Filament Coupled to ATP/GTP Hydrolysis
  Biophysical Journal, 96(6):2146-2159 - Full version
• Liverpool TB, Marchetti MC, Joanny JF, Prost J
  Mechanical response of active gels
  Europhysics Letters, 85, 18007 - Full version
• Pontani LL, Van der Gucht J, Salbreux G, Heuvingh J, Joanny JF, Sykes C
  Reconstitution of an Actin Cortex Inside a Liposome
  Biophysical Journal, 96(1):192-198 - Full version