USA Biology Olympiad (USABO) Practice Exam

A polyclonal antibody can bind to which of the following?

1. Only one type of antigen

2. Multiple molecules of the same antigen

3. Only linear epitopes of an antigen

4. All antigens in the body

The correct answer is: Multiple molecules of the same antigen

A polyclonal antibody is produced by multiple clones of B cells and can recognize and bind to several different epitopes on the same antigen. This ability arises because each B cell can produce antibodies that target distinct portions of the antigen, leading to a diverse range of binding sites. In contrast, if an antibody could only bind to one type of antigen, it would be classified as a monoclonal antibody. Similarly, polyclonal antibodies do not bind exclusively to linear epitopes; they can also recognize conformational epitopes, which are formed by the three-dimensional structure of the antigen. While polyclonal antibodies can bind to multiple molecules of the same antigen, they do not bind to all antigens in the body, as that would imply nonspecific or universal recognition, which is not characteristic of any specific antibody type, including polyclonal antibodies.