;Cell membranes play very important roles for the cell. In general, phospholipid is one of the major constituents of a cell membrane, whereas cell membranes contain many different kinds of phospholipids with different kinds of headgroups and degrees of unsaturation. In this report, we systematically compare different lipid molecules which have different headgroups and different degrees of unsaturation. We used X-ray diffraction to determine the static physical properties (such as elastic properties) of different kinds of lipid molecules, and used electron spin resonance spectroscopy to determine the dynamic physical properties (such as the dynamics of lipid hydrocarbon chains) of different kinds of lipid molecules. Finally, we used fluorescence spectrophotometer to investigate whether different lipid compositions will affect the biological function (such as membrane fusion) of lipid membranes. We want to find out the relationship between composition (including different headgroups and different degrees of unsaturation) and membrane physical property, and whether these properties will effect biological function. And we also want to know the mechanism underlying this correlation. The difference in headgroup (phosphatidylcholine(PC), phosphatidylethanolamine(PE)) has great influence on the spontaneous curvature and bending modulus, but it seems to have almost no effect on the dynamic of lipid hydrocarbon chain. And the membrane fusion rate increases with the amount of PE headgroup. Changing the degrees of unsaturation for both PE and PC headgroups has weak influence on the spontaneous curvature, but it would increase the dynamics of lipid hydrocarbon chain and decrease the bending modulus. And the membrane fusion rate was significantly decreased with increasing the degrees of unsaturation. Consequently, we found out the relationships among membrane composition, membrane physical property and biological function. Changing headgroups and degrees of unsaturation has a significantly different effect on membrane fusion rate. We speculated that there are two mechanisms which can change the fusion rate of the cell membrane. We can promote or inhibit the membrane fusion rate by changing membrane elastic energy and the dynamics of lipid molecular. This may be one of the reasons why cell membranes contain many different kinds of lipids.
