- Antibodies are proteins consisting of four polypeptide chains, two identical heavy chains and two identical light chains. Each chain is composed of segments encoded for by immunoglobulin genes. Immunoglobulin genes originally have segments for hundreds of different variable (V) regions, many different junction (J) regions, and several different constant (C) regions. - As a B cell matures, these genes rearrange to produce a unique sequence that will en code a unique antibody. - The diagram to the left shows a simplified version of DNA rearrangement in immunoglobulin genes. As the B cell differentiates, a stretch of DNA is removed from the original gene. This deletion places the V2 region next to the J region. - The DNA is then transcribed, and RNA processing takes place. The protein that will result consists of the V2 region and the J and C regions. - Keep in mind that this diagram shows only three variable regions and one J and C region. In reality there are hundreds of V regions, several J regions, and several C regions. In addition, there are two different chains (the heavy chain and light chain). Thus, millions of possible antibodies can arise from the rearrangement of antibody genes.

The site on an antibody where an antigen binds is referred to as the antibody’s variable region because:

- The region is different on different antibody molecules.

Identify the different chains of molecules in the figure below.

1. DNA of undifferentiated lymphocyte; 2. DNA of B cell; 3. pre RNA; 4. mRNA; 5. Polypeptide of antibody.

Which statement regarding antibody diversity is not true?

- Antibody diversity is partly due to clonal selection in B cell genes.

- Introns are pieces of DNA that do not code for an amino acid in a polypeptide.

12.9.2 Antibodies and DNA Rearrangement Flashcards by Irina Soloshenko

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12.9.2 Antibodies and DNA Rearrangement Flashcards

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