Describe the structure of an antibody and relate it to it's function.

An antibody is a Y shaped protein which has a constant region and a variable region. The variable region of an antibody is of a complementary shape to a specific pathogenic antigen and this allows the antibody to bind to the antigen and neutralize the pathogen. The shape of the variable region varies between different antibodies therefore different antibodies can bind different antigens. The constant region of the antibody is the same for all antibodies. The constant region allows phagocytes to bind to the antibody. This allows the antibodies to act as opsonins which means they help the pathogens to be phagocytosed by phagocytes. Antibodies also have a hinge region which increases their flexibility and allows them to bind multiple pathogens at once - this is called agglutination.