Draw a complete Ig molecule and identify antigen-binding siteson the antibody.

Describe antigen-antibody binding and it’s results. What are the 5 steps?

Addition of immunoglobulin G (IgG) specific for hemoglobin to a solution of hemoglobin results in the formation of a red precipitate. In contrast, addition of the Fab fragments from this antibody to hemoglobin results in no such precipitate. What could explain this difference in results? Treatment with papain produces Fab fragments with different antigen specificity than the original IgG molecule. IgG can simultaneously bind two different antigens, whereas an Fab fragment can only bind one antigen at a time. The Fab fragments preferentially bind to other Fab fragments rather than to hemoglobin. The hemoglobin molecule antibody-binding sites can bind IgG molecules, but cannot bind Fab fragments.