Antibodies

• Antibodies


  Globular glycoproteins called immunoglobulins
• Antibody structure


  • Quaternary structure (Y-shaped)
  • Two 'heavy' (long) polypeptide chains bonded by disulfide bonds to two 'light' (short) polypeptide chains
  • Each polypeptide chain has a constant region and variable region
• Constant regions


  Do not vary within a class (isotype) of antibodies but do vary between the classes. Determine the mechanism used to destroy the antigens
• Classes of mammalian antibodies

  • 5 classes, each with different roles
• Variable regions


  Amino acid sequence in the variable regions of the antibodies (the tips of the "Y") are different for each antibody. Where the antibody attaches to the antigen to form an antigen-antibody complex
• Antigen-binding site


  Composed of 110 to 130 amino acids, includes both the ends of the light and heavy chains. Specific to the epitope (the part of the antigen that binds to the antibody)
• A pathogen or virus may present multiple antigens meaning different antibodies need to be produced
• Hinge region


  Gives flexibility to the antibody molecule which allows the antigen-binding site to be placed at different angles when binding to antigens
• Antibodies


  Produced by B-lymphocytes
• Antibodies


  Bind to specific antigens that trigger the specific immune response. Every antigen has one antibody
• Antigens


  • Pathogens and their toxins
  • Pollen
  • Blood cell surface molecules
  • Surface proteins found on transplanted tissues
• Function of antibodies


  Destroy pathogens within the body either directly, or by recruiting other immune cells
• Ways antibodies function


  • Anti-toxins
  • Opsonins
  • Agglutinins
• Anti-toxins


  Antibodies can combine with viruses and toxins of pathogens (e.g. bacteria) to block them from entering or damaging cells
• Opsonins


  Antibodies can attach to bacteria making them readily identifiable to phagocytes, enabling phagocytosis
• Agglutinins


  Antibodies can attach to the flagella of bacteria making them less active, and cause pathogens carrying antigen-antibody complexes to clump together (agglutination)
• Antibodies


  Can create holes in the cell walls of pathogens causing them to burst (lysis) when water is absorbed by osmosis