Antibody

Antibodies are large glycoproteins that help protect the body against infection. They bind with a high degree of specificity to molecular structures (antigens) on infectious agents. This can lead to enhanced killing of microbes by phagocytes or complement.

They can be segregated into 5 classes; IgG, IgM, IgE, IgA and IgD; their class is determined by the type of heavy chain in the antibody. Each of them has different distribution in the body. IgM and IgA are multimeric. The other three are monomeric antibodies. IgA exist as both multimeric and monomeric antibody in different tissues of the body.  

Antibody molecules are in the shape of a Y, and all consist of three parts that are connected together by disulphide bonds in order to form this Y shape. Antibodies are also made up of a two polypeptide chains; a heavy chain and a light chain. All immunoglobulin molecules contain heavy and light chains that are identical, giving rise to two identical antigen-binding sites. 

Antigen-binding sites bind to epitopes on the antigen. The epitope can be linear (continuous) or conformational (discontinuous)