IMMUNOGLOBULIN STRUCTURE AND GENES THAT CODE FOR THEM Antibodies(immunoglobulins) are produced in vertebrates due to antigenic challenge They exist in two forms -Membrane bound form; on surfaces of B lymphocytes where they act as receptors -Secreted form; in circulation, mucosal sites,tissues

Structure An antibody molecule has a symmetric core structure composed of two identical light chains and two identical heavy chains. Heavy and light chains are linked together by disulfide bonds Both the light chains and the heavy chains contain a series of repeating, homologous units, each about 110 amino acid residues in length, folded due to intra chain disulphide bonds forming domains

Heavy chain has 1VH domain, 3 to 4 CH domains (CH 1, CH 2, CH 3. CH 4) The light chain has 1VL domain and 1 CL domain Both heavy chains and light chains consist of amino terminal variable (V) regions that participate in antigen recognition and carboxy-terminal constant (C) regions

  The C regions of the heavy chains mediate effector functions(biological functions) The hinge region is found only in IgG, IgA and IgD. Other Ig ie IgM and IgE instead have an extra CH4 Domain Variable regions are so named because they contain regions of variability(differences/changes) in amino acid sequence that distinguish the antibodies made by one clone of B cells from the antibodies made by other clones. There are five types of heavy chains (α,ε,γ.µ,δ) and two light chains(Kappa K and Labda L)

Digestion of Ab(Ig) with enzymes Papain-yields three fragments ie 2 identical Fab and 1 Fc Fab(Fragment antibody) Because Fragment That is Antigen Binding Fc (fragment crystalisation) Because Found To Crystallize In Cold Storage  Pepsin-yields F(ab`)2 No Fc Recovery, Digested Entirely

Revision questions? 1. The structure of an antibody is composed two chains, name them a)One of the chains has five types, name them b)The other chain has two types, name them 2.Write briefly on the following a)Constant(C) region of an antibody b)Variable(V) region of an antibody