- Antibodies can bind two identical antigens simultaneously however, IgM and IgA are multivalent 
- A foreign substance usually has many antigenic regions – places where antibodies can bind. 
- When the immune system activates, there are many different antibodies made to bind these different antigenic regions
- In this way they can cross link and form a lattice and quickens its breakdown from the immune system (i.e. B cell proliferation). 


Biochemsitry: Stimulating an Immune Response 

- Antigens (foreign substance) stimulate creation of preexisting B cell the antibodies which recognize the antigen. 
- The genes that code for antibodies are limited – so where does the diversity come from? 
- The antibody diversity is accounted from the genetic changes of the B lymphocytes development. 
- Antibodies are coded by DNA segments: V, J and C for the light chains and V, D, J and C for the heavy chains. Because there are so many segments and many versions of these segments are possible, the possibilities for antibodies are significantly large. 
- Additionally, changes occur once a B cell has encourntered an antigen and secrets antibodies. 
- The B cells divide and the antibody gene mutation increases and creates a trial of nucleotides that vary (one amino acid mutations for every cell generation) and this allows for antigen specificity of the antibody to be fine tuned over many cell generations. This antigen-binding affinity increases with the B cell proliferation. 


Diversity of Antibodies and DNA segments

- Despite having the conserved immunoglobulin fold motif, immunoglobulins can bind many different types of antigens. 
- Amino acid variations lie at the immunoglobulins antigen-binding site.  


Grand Valley State University

- “arms” of the Y-shaped antibody 
- “ab” = antigen binding because these sections contain the antigen binding sites 
- Vary from IgG to IgG in the N-terminal halves, or the very tops of the chains – contain the variable region – two on each arm


IgG Light Chain (Fab)

Voet, D., Voet, J. G., & Pratt, C. W. (2013). Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contractions, and Antibodies. In Fundamentals of biochemistry: Life at the molecular level (4th ed., pp. 176-216). Hoboken, NJ: Wiley. Retrieved February 21, 2021, from archive.org.

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