While comparing two different protein-sequencing methods requiring minute amount
ID: 79529 • Letter: W
Question
While comparing two different protein-sequencing methods requiring minute amounts of protein, you established the amino acid sequence of the entire light chain of a purified immunoglobulin. From this sequence you will be able to determine [complete the sentence and assess the resulting statements (1-6) as either factually correct (= true) or incorrect (= false)]:
1. the isotype of the immunoglobulin.
2. whether the B cell that produced this antibody received T-cell help.
3. the specific variable gene fragment used to produce this chain.
4. the antigen specificity of the immunoglobulin.
5. the approximated strength of the immunoglobulin’s binding to different Fc receptors.
6. the molecular weight of the post-translationally unmodified light chain.
Explanation / Answer
Please find the answers below and reasons in parentheses:
1. True (Since every isotype of an antibody arises form different post-transcriptional modifications, they give rise to a different set of protein. Thus, knowing the sequence of a protein, the seqeunce and thus isotype of the immunoglobulin can be determined for a species)
2. False (The process of generation of antibodies from the B cell may or may not require the help of T-cell i.e. T-helper cells. This depends upon the nature of immunogen and the mode of immune-response of the body, not on the proteins sequence of the antibody)
3. True (Since a specific gene sequence will give rise to a specific mRNA sequence and consequently, a very specific protein sequence, knowing the protein seuqence help in knowing the identity of its encoding gene)
4. False (The immunoglobulins respond to millions or countless number of antigens which are varied in types and existences. The antigens which specifically elicit immune response of same time can differ in their identity alot and thus, the nature of immunoglobulin and its protein sequence cannot determine the nature of antigen specificity for it.)
5. True (The binding of immunoglobulin to the different Fc receptors is based upon protein-protein interaction and nature of amino acids they contain. Thus, the nature of protein sequence determines the strength of antigen-antibody binding)
6. True (The statement is true since post-translational unmodified light chain of immunoglobulin will comprise of only those amino acids which are reflected by its mRNA transcript. Thus, the actual sequence of the protein can be determined to judge the nature of post-translational light chain sequence)
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