The specificity of an antibody is determined by the
(a) Fixed segment
(b) Antigenic determinants
(c) Variable region
(d) Size of the antibody
(e) Antibody class

Verified step by step guidance

1. Understand that an antibody is a Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses.
2. Recall that antibodies have different regions: the fixed (constant) region and the variable region. The fixed region determines the class of the antibody, while the variable region is responsible for binding to specific antigens.
3. Recognize that antigenic determinants, also called epitopes, are specific parts of an antigen that antibodies bind to, but they do not determine the antibody's specificity; rather, they are the target of the antibody.
4. Identify that the specificity of an antibody is determined by the structure of its variable region, which varies between different antibodies to recognize different antigens.
5. Conclude that among the given options, the variable region (option c) is the correct answer because it determines the unique antigen-binding specificity of the antibody.

Key Concepts

Antibody Structure

Antibodies are Y-shaped proteins composed of variable and constant regions. The variable region, located at the tips of the Y, is responsible for binding to specific antigens, while the constant region determines the antibody's class and effector functions.

Variable Region

The variable region of an antibody contains unique amino acid sequences that create a specific binding site for an antigen. This region's diversity allows antibodies to recognize a vast array of antigens with high specificity.

Antigenic Determinants (Epitopes)

Antigenic determinants, or epitopes, are specific parts of an antigen recognized and bound by an antibody's variable region. The interaction between the variable region and these epitopes determines the antibody's specificity.