Mechanical properties of closed lamellar membranes and cellular processes

This paper considers cellular processes that involve changes in membrane co nformation. A general overview of the relationship between the mechanical p roperties of lamellar membranes and the shapes of vesicles and cells is giv en. Variational procedures are described for calculating the equilibrium sh apes of simple vesicular objects, based on the assumption that these shapes correspond to the minimum of the sum of the membrane local and nonlocal be nding energies. The two properties of closed lamellar membranes which could form a physical basis for biological processes axe proposed to be the symm etry breaking in vesicle shape behavior and vesicle budding. The cellular p rocesses are discussed on the basis of the hypothesis that the shape behavi or of simple vesicular objects may serve as a framework for their analysis. It is proposed that the description of certain cellular processes requires the inclusion of energy contributions additional to the membrane bending e nergy, and/or the involvement of cytoplasmic structures which exert forces on the membrane. Several specific examples are used to demonstrate that suc h generalizations may help reveal the functional role of certain cell const ituents.