Antibody Structure Problem Set

Problem 4. Antigen epitopes

Tutorial to help answer the question

The epitope is defined as the part of the antigen that is recognized by antibody. The structural studies using hen egg white lysozyme as an antigen show that the epitope is:
A. a single amino acid
B. continuous, or limited to a single stretch of amino acids
C. discontinuous, or can include amino acids from non-adjacent stretches of antigen amino acids
D. the entire antigen


The epitope includes the regions of the antigen (green) that are contacted by hypervariable regions (purple) of the antibody. The hypervariable regions are on the same side of the light and heavy chains of the antibody to maximize contact with antigen, allowing strong and specific binding.


The hypervariable region has been removed in the image below. The amino acids in the framework region do not directly interact with the antigen. The role the framework region is to hold the six hypervariable loops of the light and heavy chain in position to contact the epitope on the antigen.

Animation: Antigen interacts with HV region

This animation allows you to better visualize the nature of the antigen antibody contacts.


The Biology Project
The University of Arizona
Tuesday, June 20, 2000
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