ON DEFECTS IN DIFFERENT PHASES OF TWO-DIMENSIONAL LIPID BILAYERS.

The phospholipid bilayer is the basic structure of biological membranes as well as a suitable model of a two-dimensional system. Defects within these bilayers are studied electron microscopically by application of the freeze fracture method. Topological and non-topological defects can be distinguished. The first type is analyzed in terms of the homotopy theory. Two defect systems, an Abelian and a non-Abelian, are found which are a consequence of a symmetry breaking. The effect of small amounts of impurities on the defect structure is studied. An outline of the possible biological relevance of defects is given in the last part.