31 - 3.2 Answer#2 Diversity through combinatorial assembly...

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3.2 Answer #2: Diversity through combinatorial assembly The second question -- how the myriad antigen specificities are encoded in the immunoglobulin gene DNA -- was solved by sequence analysis of homogeneous antibodies and their genes. These studies revealed that each antibody molecule is composed of four protein chains (see Figure 2): two identical large proteins (heavy chains) and two identical smaller light chains. The amino acid sequences of these chains were found to have an unusual property: the first hundred or so amino acids of each chain form a domain that is different for virtually every antibody that is sequenced ("variable" or V region), while the rest of the sequence is identical for every antibody chain of a particular class ("constant" or C region). (Among light and heavy chains there are about ten different classes of antibody chains, but the distinctions between these classes are irrelevant to this discussion.) Not surprisingly, the variable domains are involved in binding to the diverse possible antigens. The second question considered above can then be reformulated: how can the diversity of amino acid sequences of the variable regions of antibody proteins be encoded in the
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31 - 3.2 Answer#2 Diversity through combinatorial assembly...

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