Describe the antigen-antibody complex
a. Antibodies are always antigen specific. Combining sites of antigen, called antigenic determinants or epitopes react with corresponding antigen binding sites of antibodies called paratopes.
b. Specificity of an antibody for an antigen lies in its sequence of amino acids within variable regions of two chains. These are active sites of antibody where the molecules bind to specific antigens.
c. Both the arms have same amino acid sequence and therefore bind the same kind of antigen.
d. Thus each antibody can join two antigen like Lock and Key manner called antigen − antibody complex.