Proteins for Membrane Function

• Types: Integral/transmembrane proteins (span from one side of the bilayer to the other), Peripheral proteins (sit on one of the surfaces); can slide around the membrane
• Hydrophilic regions hold protein to the membrane surface and hydrophobic regions stabilise proteins within the membrane
• • Functions of proteins in membranes…
  • Receptor Sites
  • Transporters
  • Enzymes
  • Structural
  • Antigens
  • Glycoproteins and Glycolipids
• Receptor Sites: Must be on the outside surface of cell membranes and have a specific binding site for hormones, enzymes, or other chemicals complementary in shape to the protein to bind; binding then triggers other events in the cell membrane or the cell (cell signalling)
• Enzymes: Proteins that catalyse reactions in the cytoplasm or outside the cell (e.g. maltase in the small intestine), so they must be attached either on the inside or outside
• Structural: On the inside surface of cell membranes and attached to the cytoskeleton, they are involved in maintaining the cell’s shape or in changing it for cell mobility
• Antigens: On the cell surface that are identified by the immune system cells (e.g. Aand B antigen groups on erythrocytes); often have attached carbohydrates, forming a glycoprotein
• Glycoprotein: Short sugar molecule chainattached to a membrane protein (slightly more common) and Glycolipid: Short sugar molecule chainattached to a phospholipid molecule
• Glycoproteins and Glycolipids: The sugar chains project from the bilayer’s external surface only; they act as antigens/ recognition sites for specific chemicals,maintain membrane stability and aid cell attachment (to form tissues)