Bending elasticity and bending fluctuations of lipid bilayer containing an additive.

The static and dynamic behavior of a bilayer containing an additive is examined theoretically. We have proved that the amplitudes of the thermal shape fluctuations of a quasi spherical lipid vesicle depend on the value of the bending elasticity of the vesicle's membrane at free exchange of molecules between its constituent monolayers. The dependence is calculated of this bending elasticity as a function of the concentration of the additive in the low concentration domain. In the same domain, the autocorrelation function of each vesicle fluctuation mode is found to be dependent on the two-dimensional diffusion coefficient of the bilayer additive.