<p>An evidence describes the source of an annotation, e.g. an experiment that has been published in the scientific literature, an orthologous protein, a record from another database, etc.</p>
A membrane is a lipid bilayer which surrounds enclosed spaces and compartments. This selectively permeable structure is essential for effective separation of a cell or organelle from its surroundings. Membranes are composed of various types of molecules such as phospholipids, integral membrane proteins, peripheral proteins, glycoproteins, glycolipids, etc. The relative amounts of these components as well as the types of lipids are non-randomly distributed from membrane to membrane as well as between the two leaflets of a membrane.