Q.Explain the structure of immunoglobulin with suitable diagram.

Step 1. An antibody (immunoglobulin) monomer is built from four polypeptide chains: two identical light (L) chains (~25,000 Da) and two identical, larger heavy (H) chains (~50,000 Da).

Step 2. One light chain pairs with each heavy chain, and the two heavy chains join each other via disulphide (S-S) bonds, producing an overall Y-shaped structure represented as H2L2.

Step 3. The heavy chains carry a flexible hinge region near their middle, letting the two arms of the Y move somewhat independently to grip antigen at different angles.

Step 4. Each chain (H and L) runs from an N-terminal (amino) end to a C-terminal (carboxyl) end and is divided into a variable (V) region and a constant (C) region.

Step 5. On each arm of the Y, the V regions of the paired heavy and light chains fold together to form an antigen-binding site shaped to fit one specific antigenic determinant (epitope) — so each monomer has two such identical binding sites, one on each arm.

Step 6. The C regions form the stem of the Y and determine which antibody class (IgG, IgM, IgA, IgD, IgE) the molecule belongs to, along with shared effector functions common to all antibodies of that class. …

Describe the four-chain composition, bonding, and variable/constant region organisatio …