Cell recognition and the immune system

• Plasma membrane


  surrounds cell (and most organelles) and forms boundary between cytoplasm and environment, phospholipids are important components
• Extrinsic/Peripheral proteins


  proteins that don't extend right across the lipid barrier, give mechanical support or act as receptors for cell recognition, may help cells to bind/adhere together
• Intrinsic/Integral proteins


  Proteins that fully extends across the bilayer, either channels filled with water that allow water-soluble molecules through or they are carrier proteins that bind to molecules and move them through the membrane when they change shape
• Glycoproteins


  made of a carbohydrate covalently bonded to a protein, carbohydrate part extends from the bilayer into the outside of the cell, acts as a cell surface receptor for hormones and neurotransmitters, allows cell recognition, helps cells attach to one another to form tissues
• Glycolipids


  made of a carbohydrate covalently bonded to a lipid, help maintain membrane stability, carbohydrate part extend from the bilayer to the watery environment outside the cell, acts as a cell surface receptor for specific chemicals, helps cell attach to one another to form tissues
• Cholesterol


  adds strength and rigidity by limiting fatty acid tail movement, highly hydrophobic and so prevents water loss and loss of dissolved ions from cells.