Lipids and Membranes

Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The main biological functions of lipids include energy storage, as structural components of cell membranes, and as important signaling molecules.

Membrane is an enclosing or separating amphipathic layer that acts as a barrier within or around a cell. It is, almost invariably, a lipid bilayer, composed of a double layer of lipid (usually phospholipid) molecules and proteins that may constitute close to 50% of membrane content.