Biology, Eighth Edition (Raven)

Chapter 51: The Immune System

Antigenic Determinants (Epitopes)

What is the advantage of having more than one antibody attack the same structure? Antibodies recognize specific areas of antigens called epitopes. Several different antibodies can attack antigens in different areas. If an antigen evolves a different structure a specific antibody may no longer be able recognize and bind to it. The antigen is much less likely to evolve differences at all the different binding sites than at just one epitope. Having multiple antibodies for a single antigen makes it more difficult for pathogens to evolve a form that is not recognized by the host. The coating of an antigen with multiple antibodies also means that it may be recognized and destroyed more rapidly by other components of the immune system.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Antigens

		A)	have molecular weights of around 1000
		B)	have one antigenic determinant (epitope).
		C)	are considered normal by the immune system
		D)	are made up of many antigenic determinants (epitopes)
		E)	are usually made of lipids

2.	Bacterial cells

		A)	have one identifiable antigen that binds antibody
		B)	have two epitopes per cell
		C)	have many different epitopes, which each bind to specific antibodies
		D)	have many different epitopes, which all bind to the same antibody
		E)	are not antigenic

3.	An individual antibody is made against

		A)	a whole bacterial cell
		B)	one epitope on the cell
		C)	one antigen on the cell
		D)	all of the combined antigenic determinants on a cell
		E)	the cell’s DNA

4.	Each antigen has one epitope.

		A)	True
		B)	False

5.	Many different antibodies can be made against a single antigen.

		A)	True
		B)	False