Antigen & Antibody:
While discussing about ‘self’ and ‘non-self’, we got a broad idea of antigen.
Definition and Properties of an antigen
An antigen is any foreign molecule that can trigger a specific immune response. Most antigens are either proteins or very large polysaccharides. Another term ‘immunogen’ is also used for antigen. However, there is a slight difference between the two.
Paratopes and Epitopes : The part of antibody molecule which makes contact with the antigen is termed the paratope. The part of antigen molecule that makes, contact with paratope is called the epitope. There may be a series of epitopes on on an antigen. Such epitope clusters are called ‘antigenic determinant’.
Requirements for becoming an antigen
- Substance should be foreign to the host.
- Molecular weight of molecule should be 10,000 Dalton or more.
- It should possess chemical complexity.
Antibody: Definition and properties
Antibody is a protein molecule produced in animals in response to an antigen. Antibodies belong to the category of proteins called immunoglobulin. Each antibody molecule is composed of four interlinked polypeptide chains. The two long chains are called heavy chains, and the two short chains are called light chairs An antibody has a “stem” called “Fc” portion which comprises the lower half of the two heavy chains and two “prongs” (the amino acid sequences that bind antigen”. The amino acid sequences of Fc portioff are identical (constant) for all antibodies of same class. In contrast amino acid sequences for antigen binding site vary from antibody to antibody in a given class.
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