Semiflexible polymers confined in soft tubes.

We discuss various conformations for a polymer (of persistent length l(p)) confined into a deformable tube (the wall being a lipid bilayer with a certain surface tension sigma and curvature energy K). Our study assumes that there is no adsorption of the chain on the wall. Three states are compared: (a) an unperturbed tube, plus a confined chain, (b) a tube swollen in all the region surrounding the chain (similar to a snake eating a sausage), (c) a globule, a roughly spherical coil surrounded by a strongly deformed tube. We construct a (qualitative) phase diagram for these systems with two variables: the surface tension sigma and the degree of polymerization N. Our main conclusion is that "globules" usually win over "snakes".