Which part of the antigen do antibodies bind to?

Antibodies specifically bind to regions on the antigen known as epitopes. An epitope is the distinct part of an antigen that is recognized by the immune system, specifically by antibodies or T-cell receptors. This binding is crucial for the immune response, as it allows antibodies to identify and neutralize pathogens such as bacteria and viruses. The unique structure of each epitope enables antibodies to distinguish between different antigens, ensuring that the immune system can target a wide array of threats effectively.

Other terms in the options, such as fragment, substrate, and enzyme, do not accurately represent the part of the antigen that antibodies interact with. While antibodies can recognize larger fragments of antigens, it is the specific epitope within those fragments that is critical for the binding process. Understanding the role of epitopes in antibody-antigen interactions is essential in immunology and for applications like vaccine development and therapeutic antibodies.