15- Immunoglobulin Genes and Generation of Diversity

Question 1

Describe the genetic basis of generation of diversity for antigen specificity

Answer 1

Mammals can produce thousands of different antigen receptors on B and T cells. Multiple genes code for each receptor chain. Several genes code for the variable region, where only one codes for the constant region. The single constant region genes can be combined with any one of the variable region genes to make a complete receptor chain. Antigen receptor chains may be paired in different combinations to yield even greater diversity= combinatorial association

Question 2

Explain how VJ and VDJ gene recombination generated Ig diversity

Answer 2

Random selection of one gene from each of the several gene groups. There are many combinations of selected genes, leading to genetic diversity

Question 3

Explain how base deletion generates Ig diversity

Answer 3

Random removal of nucleotides from the cut ends of the genes. This results in the precise nucleotide at which V and J join varies, leading to changes in the nucleotide sequence and variations in the amino acid sequence of the V region

Question 4

Explain how base insertion generates Ig diversity

Answer 4

Additional nucleotides may be inserted at the V-D and D-J splice sites- leading to variation in the amino acid sequence

Question 5

Explain how combinatorial association generates Ig diversity

Answer 5

The ability for multiple combinations of a single constant region with several variable regions to make a complete receptor chain, leading to greater diversity

Question 6

Explain how receptor editing generates Ig diversity

Answer 6

B cells are able to continue to rearrange their V, D, J genes even after exposure to an antigen. This receptor editing will eliminate receptors that bind to self-antigen

Question 7

Explain the genetic basis for antibody classification switching

Answer 7

In the heavy chain (IGH) of B cells during the assembly process, IgM is the initial Ig created as it is the first reporting Ig when a B cell is first responding. As the immune response progressed, responding B cells then switch to using genes for IgD, IgG, IgA, and IgE

Question 8

Define somatic mutation

Answer 8

Somatic mutation is the process of mutations being made in the rapidly proliferating B cell within its DNA that encodes for the antigen binding region of the antibody produced . As a result, you will have antibodies with different affinities for the same antigen.

Question 9

What is the difference between somatic mutation and receptor editing

Answer 9

Somatic mutation: changing the constant region
Receptor editing: changing the variable region

Question 10

Describe gene conversion

Answer 10

Many pseudogenes exist upstream and will insert into the variable (V) region to cause an increase in diversity

Question 11

The shape of the antigen-binding groove depends on what?

Answer 11

The sequence of the amino acids that line the groove