The mechanical behaviour of cell membranes as a possible physical origin of cell polarity.

The mechanical behaviour of a closed layered membrane enclosing a structureless interior is considered. The shape of such an object in flaccid conditions is determined theoretically by assuming that it corresponds to the minimum value of the membrane bending energy. The symmetry breaking properties of this system are revealed. It is suggested that a continuous transition from an axisymmetrical shape involving mirror symmetry with regard to the equatorial plane of the object to the shape with polar asymmetry could be the primary event in establishing cell polarity.