Structure of Antibody

Antibodies, also called immunoglobulins (Igs), are highly specific glycoproteins produced by plasma cells (themselves derived from activated B-lymphocytes) in response to antigenic stimulation — mature plasma cells can churn out antibody molecules at the extremely rapid rate of about 2,000 molecules per second.

Structure : Structurally, an antibody is a 'Y'-shaped molecule built from four polypeptide chains: two identical, longer heavy (H) chains and two identical, shorter light (L) chains. These four chains are held together by disulfide bonds (-S-S-), and the region where the two arms join the stem of the 'Y' is called the hinge. Each chain — heavy or light — is itself divided into two regions: a variable region, which differs from antibody to antibody, and a constant region, which does not. The variable regions of a paired heavy and light chain together form the antigen-binding site, also called the paratope; because most antibodies have two arms, each with its own antigen-binding site, antibodies are described as bivalent. Small differences in the amino-acid sequence of the variable region are what make each antibody uniquely specific for one particular antigen.