Question

Compare and contrast the generation of diversity in antibody molecule binding pockets and in T cell receptor peptide-binding clefts. any info appreciated

Answer 1

ANSWER:-

Antibodies

The basic structure of antibodies (immunoglobins) is shown by the diagram to the right. It represents specifically an antibody of the IgG class. Other classes we will study are IgM, IgA and IgE. All of these are built from the basis Y-shaped structure shown to the right. Observe that are four polypeptide chains; two identical light chains and two identical heavy chains. Notice especially the two identical binding sites for a specific antigen.

To the left, one bar represents the polypeptide chain of a heavy chain and another the polypeptide cain of a light chain. The divisions in each bar represent the domains that comprise each chain. The heavy chain has four domains, while the light chain has two. The variable domains differ in antibodies of the same class that bind different antigens. Particularly important in this figure are the hypervariable regions of the variable domains. These are the portions of the light and heavy chains that allow a specific antobody molecule to bind a specific antigen.

T Cells Receptors

T Cell receptors are likewise formed from constant and variable domains. But in this case, there is only one binding site. Moreover, T cell receptors are always attached to a membrance by transmembrance domains.

Molecular Structure of Antibodies and T Cell Receptors

• both are based on a beta-sheet secondary structure. All molecules of the immunoglobin family are constructed from similar domains.   
• In the variable domain, the hypervariable regions are found in the loops that extend between the portions from the beta sheet structure. These loops are the portions that specifically bind the antigen. By necessity, the portions of the polypeptide chain that create the bete-sheet secondary structure are conserved.

Finally, observe the actual three-dimensional structure of the two variable domains of an antibody binding an antigen. Notice the precise "lock and key" relationship between the antigen and antibody. (The antigen, in this case, is a specific portion of an envelope protein of the HIV virus binding to a corresponding anti - HIV antibody).

The generation of diversity in immunoglobulins... Furthemore, the response even to a simple antigen-bearing a single antigenic determinant is diverse, comprising many different antibody molecules each with a unique affinity, or binding strength, for the antigen and a subtly different specificity.

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