3. Alternative Splicing (20 points) The human -tropomyosin gene is alternatively

Question

3. Alternative Splicing (20 points) The human -tropomyosin gene is alternatively spliced to produce several forms of - tropomyosin mRNA in various cell types (see below). For all forms of the mRNA, the encoded protein sequence is the same for exons 1 and 10. Exons 2 and 3 are alternative exons used in different mRNAs, as are exons 7 and 8. Which of the following statements about exons 2 and 3 is the most accurate? Is that statement also the most accurate one for exons 7 and 8? Explain your answers. (A) HUMAN -TROPOMYOSIN GENE 4 5 6 910 23 78 11 12 13 (B) FOUR DIFFERENT SPLICE VARIANTS Alternatively spliced mRNAs from the human -tropomyosin gene. (A) Exons in the human -tropomyosin gene. The locations and relative sizes ofexons are shown by the blue and red rectangles. (B) Splicing patterns for four -tropomyosin mRNAs. Splicing is indicated by lines connecting the exons that are included in the mRNA. (a.) (b.) Exons 2 and 3 must have the same number of nucleotides Exons 2 and 3 must each contain an integral number of codons (that is, the number of nucleotides dived by 3 must be an integer). (c.) Exons 2 and 3 must each contain a number of nucleotides that when divided by 3 leaves the same remainder (that is, 0, 1, or 2).

Explanation / Answer

If 2 and 3 are alternative exons then they must be so by maintaining the function of the protein and that can be if the amino acid sequences are not much different. So the basic requirement is the congruency of the number of amino acids which can be from a congruent number of codons which can come from a congruent number of nucleotides. hence (a) and (b) are must-have for the sequences.

Yes the same shall be applicable for 7 and 8 as well.

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