B1.1.7 Role of glycoproteins in cell–cell recognition Notes

Glycoproteins Are The “ID Badges” of Cells

1. Structure: The carbohydrate chains typically protrude from the cell surface, acting as identifiers for other cells.
2. Function
   1. Cell–Cell Recognition: Like ID badges, glycoproteins enable cells to recognize and distinguish each other as “self” or “non-self.”
   2. Tissue Organization: During embryonic development, glycoproteins ensure cells attach in the correct location to form tissues.
   3. Immune Defense: Immune cells use glycoprotein “barcodes” to detect and eliminate pathogens or infected cells.
   4. Blood Type Compatibility: Glycoproteins on RBCs determine blood groups (e.g., ABO system).

How Does Cell–Cell Recognition Work?

1. Carbohydrate “Barcodes”: The carbohydrate portion of glycoproteins is diverse, providing a unique marker for each cell type.
2. Receptor Interactions
   1. When one cell encounters another, receptor proteins on the first cell’s membrane bind to specific carbohydrate chains on the glycoprotein of the second.
   2. This lock-and-key interaction ensures high specificity in recognizing cell identity.

ABO Blood Group System: A Case Study in Glycoprotein Recognition

1. Antigens on RBCs
   1. Type O: Carries a base glycoprotein (antigen O).
   2. Type A: Has an N-acetylgalactosamine added to antigen O.
   3. Type B: Has a galactose added to antigen O.
   4. Type AB: Possesses both modifications (A and B).
2. Why It Matters
   1. Type O is called the “universal donor” since it lacks A or B modifications that might trigger an immune response.
   2. Type AB is the “universal recipient,” having both antigens and therefore no antibodies against A or B.
3. Immune Response
   1. People naturally produce antibodies against non-self antigens.
   2. Mismatched blood transfusions can lead to agglutination (RBC clumping) and severe complications.