The cell is highly organized with many functional units or organelles. Most of these units are limited by one or more membranes. To perform the function of the organelle, the membrane is specialized in that it contains specific proteins and lipid components that enable it to perform its unique roles for that cell or organelle. In essence membranes are essential for the integrity and function of the cell.
Membrane components may:
regulate transport in and out of cell or subcellular domain
allow selective receptivity and signal transduction by providing transmembrane receptors that bind signaling molecules
allow cell recognition
provide anchoring sites for cytoskeletal filaments or components of the extracellular matrix. This allows the cell to maintain its shape and perhaps move to distant sites.
help compartmentalize subcellular domains or microdomains
provide a stable site for the binding and catalysis of enzymes.
regulate the fusion of the membrane with other membranes in the cell via specialized junctions )
provide a passageway across the membrane for certain molecules, such as in gap junctions.