Anatomy of an Antibody

An antibody, also known as an immunoglobulin, is a Y-shaped protein produced by the immune system in response to the presence of antigens. Antibodies play a critical role in the immune response by recognizing and binding to specific antigens, marking them for destruction by other immune cells.

Structure of an Antibody

An antibody consists of two light peptide chains and two heavy peptide chains, making a total of four chains. These chains are held together by disulfide bonds, creating a stable and functional structure. The light chains are shorter in length compared to the heavy chains.

Light Peptide Chains

- An antibody has two identical light peptide chains, also referred to as the L chains.
- Each light chain is composed of approximately 220-230 amino acids.
- Light chains are further divided into two regions: the variable region (VL) and the constant region (CL).
- The variable region contains antigen-binding sites that interact with specific antigens.
- The constant region determines the antibody's class or isotype.

Heavy Peptide Chains

- An antibody has two identical heavy peptide chains, also referred to as the H chains.
- Each heavy chain is longer than the light chain and consists of approximately 440-450 amino acids.
- Similar to light chains, heavy chains are divided into two regions: the variable region (VH) and the constant region (CH).
- The variable region contains antigen-binding sites that complement those of the light chains.
- The constant region determines the antibody's class or isotype.

Role of the Chains

- The heavy and light chains together form the antigen-binding fragment (Fab) of the antibody.
- The Fab region is responsible for recognizing and binding to specific antigens.
- The constant regions of the heavy chains form the antibody's crystallizable fragment (Fc), which interacts with various immune cells and molecules to initiate immune responses.

Summary

An antibody is composed of two light peptide chains and two heavy peptide chains. The light chains are shorter and consist of variable and constant regions, while the heavy chains are longer and also have variable and constant regions. Together, these chains form the antigen-binding fragment (Fab) and the crystallizable fragment (Fc), allowing antibodies to recognize and neutralize specific antigens.