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AS: BIOL1
ANTIGENS AND ANTIBODIES
ANTIGENS
An antigen is a molecule that is recognised as
__________ by the immune system and triggers
an immune response.
They are large complex molecules such as
______________, _________________ and
______________.
They are located on the
_____________________________.
ANTIBODY
Antibodies are _______________ found in plasma, tissue fluid and milk.
They can bind specifically to _________________.
They are also called IMMUNOGLOBULINS.
They are produced by__________________ .
Each B cell can produce antibodies at a rate of 1000 per second for 4 days. There are hundreds of
thousands of B cells; so during the immune response to an infection there are an enormous number of
antibodies in the body making it highly likely that every antigen will be targeted.
Structure
The structure of an antibody is shown below.
The variable region of the antibody is the part that combines with the antigen. There is a 3-D fit between
the amino acid chain in the antibody and the antigen. (This is similar to the fit between an enzyme and its
substrate.)
AS: BIOL1
How antibodies work
Antibodies have 2 antigen-binding sites (one on each arm of the Y), each of which can combine with a
separate antigen molecule to form a lattice like structure called an antibody-antigen complex.
How do antibodies lead to the destruction of pathogens?
Questions:
1.
Name the monomer making up the chains which form the structure of an antibody and the bonds
holding them together.
2.
Each antibody can form a complex with only one type of antigen. Explain why.
3.
The hinge region of the antibody allows both ends to pivot and rotate in relation to one another.
Suggest how this action assists the role of antibodies in agglutination.
4.
Which types of cells produce antibodies?
5.
Is the production of antibodies a specific or non-specific defence mechanism?
6.
Why don’t antibodies cause the destruction of the body’s own cells?