ABSTRACT
Membranes form boundaries around the cell and around distinct subcellular compartments. They act as selectively permeable barriers and are involved in signaling processes. All membranes contain varying amounts of lipid and protein and some contain small amounts of carbohydrate. All membranes contain two basic components: lipids and proteins. Lipids were originally classified as biological substances that were insoluble in water but soluble in organic solvents such as chloroform and methanol. Biological membranes are not just homogeneous mixtures of lipids and proteins. Within them are discrete domains in which certain lipids and proteins cluster together to form structural and functional units. Membrane lipids are amphipathic molecules as they are made up of hydrophobic fatty acid chains and a hydrophilic polar headgroup. Lipid bilayers will spontaneously self-assemble in aqueous solution. The major driving force behind this is the hydrophobic effect – the hydrophobic fatty acid chains avoid coming into contact with the water molecules.
