General ---------Biology----------------------------------------------------- ------------------Online---------------------------------- Ch. 8 Membrane Structure and Function

Some glycoproteins (proteins combined with short chains of sugars) serve as identification tags that are specifically recognized by other cells.

Your white blood cells recognize invading bacteria by "reading" the glycoproteins on the surface of the bacterial cell.  When your white blood cells encounter a foreign glycoprotein, they trigger the production of antibodies and legions of new white blood cells to fight the infection.  The antibodies are proteins.  Each antibody protein has several active sites that match the foreign glycoprotein.  This allows one antibody molecule to attach to several bacteria cells causing them to clump up around the antibody molecule.  The white blood cells then can efficiently ingest the clumped up bacteria by phagocytosis.  This mechanism is one of the immune system responses.

If you are blood Type A, then you have a glycoprotein on the surface of your blood cells that is called the "A glycoprotein."  If you get a transfusion of Type B, your white blood cells encounter the "B glycoprotein" and assume it is a foreign invader and attack it with the immune systems response.  When a patient "rejects" an organ transplant, the mechanism of rejection is a similar immune systems response, when your white blood cells produce antibodies against the glycoproteins on the cells of the transplanted organ.

Hormones produced by your brain travel through the body in the blood stream and "recognize" the tissue where they will stimulate activity by binding to specific glycoproteins that occur nowhere else but on the surface of that tissue.  Medicines also use glycoproteins to "recognize" when they bump into their intended tissue (cartoon).