Antigen-Antibody Complex (AQA AS Biology) : Revision Note

Antigen-Antibody Complex

• An antigen and its complementary antibody have complementary molecular shapes

  • This means that their molecular structures fit into each other

• When an antibody collides with a foreign cell that possesses non-self antigens with a complementary shape, it binds with one of the antigens

• When this occurs the two molecules combine to form an antigen-antibody complex

• Y-shaped antibodies have two antigen-binding sites, meaning that they can bind to more than one antigen at the same time

  • This can cause groups of the same pathogens to become clumped together in agglutination

• The binding of antibodies to antigens either neutralises the pathogen or acts like a marker to attract phagocytes, which engulf and destroy the pathogens

  • Due to agglutination, phagocytes can often phagocytose many pathogens at the same time, as they are all clumped together