ABSTRACT
Integral membrane proteins are tightly associated with the hydrophobic core of the lipid bilayer and can be removed from it only with organic solvents or detergents that disrupt the membrane structure. Integral proteins are asymmetrically distributed across the membrane and are usually free to move in the plane of the bilayer by lateral and rotational movement, but are not able to flip from one side of the membrane to the other. Some integral proteins have multiple membrane-spanning α-helices. Membrane proteins are classified as either peripheral or integral depending on how tightly they are associated with the membrane. Peripheral membrane proteins are less tightly bound to the lipid bilayer than integral membrane proteins and can be readily removed by washing the membranes with a solution of high ionic strength or high pH. The extracellular surface of the plasma membrane is often covered with a protective coat of carbohydrate.
