Antigens and Antibodies

Antigens

• Large protein molecules
• Often found as glycoproteins in cell membranes or cell walls
• Used to identify cells
• Example: Structure of cell membrane and glycoproteins as antigens for identifying specific bacteria
• Genetically controlled
  • Closely related cells have more similar antigens than unrelated cells

Antibodies

• Secreted by B-cells (a type of lymphocyte)
• Y-shaped protein molecules
  • Two binding sites at the ends
  • Binding sites attach to antigens on foreign bacteria
• Cause agglutination (clumping) of bacteria
  • Agglutinated bacteria are identified, engulfed, and digested by phagocytic leukocytes
• Specific antibodies bind to specific antigens
  • Refer to standard 6.3.4 for additional information