Which molecule binds specifically to an antigen during an immune response?

The molecule that binds specifically to an antigen during an immune response is an antibody. Antibodies, also known as immunoglobulins, are produced by B cells (a type of white blood cell) in response to the presence of an antigen, which can be a foreign substance such as a pathogen or a toxin. The structure of an antibody allows it to recognize and bind specifically to a unique part of the antigen known as an epitope. This binding is crucial for the immune response, as it helps to neutralize the pathogen, mark it for destruction by other immune cells, or prevent its entry into cells.

On the other hand, enzymes are biological catalysts that speed up chemical reactions, but they do not interact with antigens in a specific manner. Antigens themselves are molecules that trigger an immune response, but they do not have the ability to bind to other antigens. Hormones are signaling molecules that regulate physiological processes and functions in the body, lacking the specific binding role with antigens that antibodies exhibit. Thus, the specific and critical role of antibodies in recognizing and binding to antigens highlights their importance in the adaptive immune response.