The biological membranes provide much of the functionality of the organisms of which they are a part. From intracellular organelles to extracellular cellâcell interactions, membranes provide the structures necessary for biological function and organisation. Many structural and functional features are common among membranes in archaea, bacteria, eukaryotic cells and enveloped viruses. The fundamental architecture of all biological membranes is built upon the lipid bilayer. Thus, all membranes have properties in common. Membrane proteins confer a myriad of specific functions expressed by cell membranes. Plasma membranes determine the cell boundary and the interactions of the cell with its environment. Intracellular membranes compartmentalise cells into different functional units with differing internal compositions.