Biology - Antibodies

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Antigens are molecules that can stimulate an immune response. Almost any molecule could act as an antigen. Antigens are usually large molecules that have a specific shape. A foreign antigen will be detected by the immune system and will stimulate the production of antibodies. These antibodies will be specific to the antigen. As the antigen is specific to the organism, we can think of the antibody as being specific to the pathogen. Antigens are usually a protein or glycoprotein in or out of the plasma membrane (cell surface membrane). Our own antigens are recognised by our immune system and do not stimulate any response.



Antibodies are molecules produced by the lymphocytes in the immune system. They are released in response to an infection. Antibodies are large proteins and are also known as immunoglobulins. They have a specific shape that is complimentary to that of a particular antigen.  Therefore antibodies are specific to particular antigens. Our immune system must manufacture one type of antibody for every antigen that is detected. Antibodies attach to antigens and render them harmless.


The structure of an antibody:

Antibody molecules are Y-shaped and have two distinct regions. The structure of an antibody molecule includes the following features:

·         Four polypeptide chains held together by disulfide bridges.

·         A constant region, which is the same in all antibodies. This enables the antibody to attach to phagocytic cells and helps the process of phagocytosis.

·         A variable region, which has a specific shape and differs from one type of antibody to another. This is the result of its amino acid sequence. It ensures that the antibody can attach only to the correct antigen. The shape of the variable region is complimentary


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