Final answer:
The hypervariable regions or complementary determining regions (CDRs) of an antibody are located in the variable regions of the heavy and light chains. They enable antibody specificity by forming an antigen-binding surface and display high variability, providing the ability to bind to a multitude of different epitopes.
Step-by-step explanation:
The hypervariable regions, also known as complementary determining regions (CDRs), are located in the variable region of an antibody's heavy and light chains. In the heavy chains, these regions are found at positions 31-37, 51-68, 86-91, and 101-109. They are held in place by more conserved framework regions, comprising 80-85% of the structure, whereas the hypervariable regions make up about 15-20%. These hypervariable regions form an antigen-binding surface when the variable regions of the light chain and the heavy chain come together in three-dimensional space, thus determining the specificity of the antibody to its corresponding epitope.
Antibodies are composed of two identical heavy chains and two identical light chains, linked by disulfide bonds, presenting a 'Y' shape. The antigen-binding sites, accounting for the antibody's specificity, are located at the far end of the arms of the Y, known as the Fab region. These regions have a high degree of variability and are essential for the antibody's diverse functions such as neutralization of pathogens, agglutination, and antibody-dependent cell-mediated cytotoxicity.
Moreover, antibody diversity is ensured by the mutation and recombination of gene segments that encode these variable domains in B cells. The diversity of the variable domains in the light and heavy chains of the antibody molecule allows for the formation of millions of unique antigen-binding sites, enabling the immune system to recognize a vast array of antigens.