Structure and Antigen Binding Sites
Start with the big picture
An immunoglobulin has two identical heavy chains and two identical light chains joined by disulfide bonds. Variable domains from both chain types meet to form the antigen-binding site, with three complementarity-determining regions from each chain shaping recognition. The hinge region allows the Fab arms to move, while the Fc portion supports effector functions. The lesson also relates structure to antibody classes and binding: isotype switching changes the Fc region while preserving antigen specificity, and affinity describes one epitope–paratope interaction whereas avidity describes the combined strength of multivalent binding. These distinctions provide a foundation for understanding antibody function and selected clinical associations.
What you'll learn
- Describe the basic heavy- and light-chain organization of an immunoglobulin.
- Explain how variable domains and CDRs contribute to antigen recognition.
- Distinguish Fab and Fc regions by structure and function.
- Differentiate affinity from avidity and relate each to antibody binding.
- Explain how isotype switching affects Fc structure without changing antigen specificity.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
