What would happen to immunoglobulin genes if alternative mRNA splicing was nonfunctional?

Question

A.  Transcripts would contain a single V region only.
B.  Transcripts would contain all possible V, D, J, and constant regions.
C.  Transcripts would have extra V, D, and J segments attached to a single constant region.
D.  Transcripts would have single V and D segments, but extra J segments and constant regions.


Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?
 
Gather Content
What do you already know about mRNA splicing? What other information is related to the question?
 
Choose Answer Given what you now know, what information is most likely to produce the correct answer?
 
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

D.  Transcripts would have single V and D segments, but extra J segments and constant regions.

Clarify Question
What is the key concept addressed by the question?
        · This question is asking about the consequences to immunoglobulins of alternative splicing of mRNA.
What type of thinking is required?
        · Analyze level:
            o This is an analyze question because you have to break alternative splicing of mRNA and the nature of immunoglobulins into their component pieces to understand how they function.
 
Gather Content
What do you already know about mRNA splicing? What other information is related to the question?
        · Immunoglobulins, or antibodies, have variable regions that recognize specific antigens, as well as constant regions that are similar for different antibodies.
        · Many different combinations are possible for the variable regions.
        · The DNA sequence that codes for the heavy chains of immunoglobulins has approximately 50 V segments, 30 smaller D segments, and 6 smaller J segments.
        · Each segment codes for a different series of amino acids.
        · In the synthesis of a heavy chain of an immunoglobulin, a V, D, and J region are randomly selected and joined together.
        · In the synthesis of immunoglobulins, heavy-chain-encoding pre-mRNA transcripts start at the rearranged VDJ and continue through exons encoding m and d constant regions.
        · Light chains are synthesized in a similar, way except they lack a D segment.
 
Choose Answer Given what you now know, what information is most likely to produce the correct answer?
        · Alternative splicing of tRNA transcripts removes any extra J segments that remain 3¢ to the rearranged VDJ, as well as either d or m sequences, resulting in transcripts that all encode the same variable region but either m or d constant region exons, respectively.
        · Translation results in a m or d heavy-chain polypeptide, which associates with a light-chain polypeptide in the rough endoplasmic reticulum.
        · Thus, the mature naive B cell expresses both IgM and IgD on its surface, both having the same antigen-binding specificity..
 
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Analyze level:
            o Answering this question correctly depended not only on distinguishing between the constant and variable regions of an antibody, but on your ability to break down, or analyze, alternative splicing. If you got an incorrect answer, did you remember that components of the variable region include many different possible combinations, or that alternative splicing of mRNA can accommodate this variation? Did you have trouble breaking down the nature of antibodies to determine the correct answer?