Antibodies = proteins synthesised by B cells.
When body is invaded by non-self material, B cell produces antibodies that react with antigens on surface of non-self material by binding to them precisely.
Antibodies are very specific (although molecule is flexible rather than rigid like the induced fit model of enzyme activity) and each antigen has its own antibody.
Massive variety of antibodies is available - made from proteins.
Antibodies = four polypeptide chains - one pair are long (heavy chains) and one pait are short (light chains). Antibodies are Y-shaped.
So the antibody can fit around the antigen, they can change shape by moving as if they had a hinge at the fork of the Y-shape.
Antibodies' binding site fits very precisely onto antigen = forms antigen-antibody complex.
Binding site is variable on different antibodies = variable region (top of each fork of Y).
Each site consists of a sequence of amino acids that form a specific 3D shape, binds directly to single type of antigen.
Rest of antibody is the same on all antibodies = constant region.
Bacterium or other micro-organism entering the body can have many hundreds of different antigens on its surface - each inducing a different type of B cells to multiply and clone itself.
Each clone produces…