Antibodies, also known as immunoglobulins, are Y-shaped proteins that play a critical role in the immune system's defense against pathogens. Their intricate structure allows them to specifically bind to antigens, foreign molecules that trigger an immune response.
SUBUNIT COMPOSITION:
- Antibodies consist of four polypeptide chains:
- Two heavy chains, longer and structurally similar (around 440 amino acids each).
- Two light chains, shorter and identical (around 220 amino acids each).
CHAIN ARRANGEMENT:
- These chains are linked together by disulfide bonds (strong covalent bonds) and non-covalent interactions (weaker bonds) to form the characteristic Y-shape.
- The arms of the Y are formed by the N-termini (ends) of the heavy and light chains coming together, creating the antigen-binding fragments (Fab).
- The base of the Y is formed by the C-termini (opposite ends) of the heavy chains, known as the fragment crystallizable (Fc) region.
FUNCTIONAL REGIONS:
- Variable (V) regions: Located at the N-termini of both heavy and light chains, these regions are highly variable in their amino acid sequence. This variability allows the Fab regions to recognize and bind to specific antigen shapes with remarkable precision.
- Constant (C) regions: The C-termini of the heavy chains have a more constant amino acid sequence. This region determines the antibody class (IgG, IgM, IgA, etc.) and influences how the immune system interacts with the antigen.
