Isolation, composition and general structure of membranes

This chapter outlines the history of plasma membrane and discusses the isolation, composition, and general structure of membranes. Some studies of membrane structure can be made using membranes organized into cells; such studies include microscopical examination of membrane organization in cells and of membrane–cytoskeletal interactions, X-ray diffraction analysis of cells, which possess ordered membrane arrays, some types of measurement of the mobilities of membrane components, and labeling experiments designed to probe the asymmetric orientations of surface membrane components. However, purified membrane preparations are needed for most studies of the chemical composition or spatial organization of membranes. For studies of chemical composition, the chief criterion is that membrane preparations should be pure samples of a single type of membrane but studies of membrane structure also demand that samples of isolated membranes should preserve the spatial interrelationships between different molecules that prevail in the intact, healthy cell.