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. Most integral proteins have one or more regions of the polypeptide chain that traverse the lipid bilayer. Peripheral membrane proteins are only loosely bound to the membrane and can readily be removed by washing the membranes with a solution of either high ionic strength or high pH. These treatments disrupt the noncovalent ionic and hydrogen bonds holding the peripheral proteins on the surface of the membrane. Sugar residues are found only on the extracellular side of the plasma membrane attached either to lipids to form glycolipids or to proteins to form glycoproteins. The carbohydrate forms a protective coat on the outer surface of the cell and is involved in intercellular recognition.
