Antibody structure simplified

"Antibodies are weapons used by the B cell."
An antibody is a large Y-shaped protein produced by B cells.
Polypeptide chains: Each antibody is made of four polypeptide chains (also known as Y shaped tetrapeptide protein). Of these, two chains are heavy chains (H) & two are light chains (L).

Each arm of the Y contains a complete L chain and a part of H chain and leg of the Y contains the remaining parts of the H chain.

Ends of the polypeptide chains: One end of each chain is called amino terminal end or N-terminal and the other is called the carboxy terminal end or C-terminal.

Each chain has two regions the variable region and a constant region.

The variable region: It is located at the tip of each arm of the Y-molecule in the N terminal end. It is different for each class and subclass.

Antigen binding site: The variable region of the heavy chain (VH) and variable region of the light chain (VL) together form the antigen binding site for interaction with a homologous antigen molecule.

The constant region: It is located at the base of the stalk of the Y in C terminal end.

Disulfide bonds: The four chains are held together by disulfide bonds. A disulfide bond holds each light chain to a heavy chain.

Hinge region: Two disulfide bonds also link the midregion of the two heavy chains, this part of the antibody displays considerable flexibility and is called the hinge region (This helps the antibody to bind to two epitopes simultaneously which are some distance apart).

Stem region: Beyond the hinge region, parts of heavy chain from the stem region.

Heavy chains: The heavy chains of a given antibody molecule determine the class of that antibody: IgM( μ), IgG(γ ), IgA(α ), IgD( δ), or IgE(ε ).

Light chains: Each class can have either kappa (κ) or lambda (λ) light chains.

That's all!