1. Clonal Selection

2. Antibody Structure Made up of 4 polypeptide chains Made up of 4 polypeptide chains –2 identical heavy chains –2 identical light chains Each half of antibody is made up of 1 light chain and 1 heavy chain Each half of antibody is made up of 1 light chain and 1 heavy chain 1 antibody has 2 antigen- binding sites 1 antibody has 2 antigen- binding sites

3. Variable region of Antibodies Thousands of B cells Thousands of B cells –Each w/ a different receptor Receptor binds to complementary shape of antigen Receptor binds to complementary shape of antigen

4. Clonal Selection When a T or B cell binds an antigen When a T or B cell binds an antigen Proliferates Proliferates Clonal selection Clonal selection –All of descendants will have same antibody –Only those clones that bind to antigen will divide

5. Genetic Diversity Over 18 billion possible different antibodies Over 18 billion possible different antibodies 2 types of light chains 2 types of light chains –Lambda  2 Variable, 4 Junctions, 4 Constant regions –Kappa  300 Variable, 5 Junction, and 1 Constant region gene 5 types of heavy chains 5 types of heavy chains –IgM, IgD, IgG, IgE and IgA, –V,D,J, C regions