15 - BIO 305 Problem set for lecture 15 Winter 2008 1(C...

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BIO 305 Problem set for lecture 15 Winter 2008. 1. (C level) You are studying a yeast gene that encodes two different transcripts. The exons and their respective lengths are shown below. The only difference between the two transcripts is that alternative splicing allows either exon #2a or exon #2b to be included in the final message. Transcript A exon#1(9 nt) exon#2a(33 nt) exon#3(242 nt) exon#4(198 nt) Transcript B exon#1(9 nt) exon#2b(21 nt) exon#3(242 nt) exon#4(198 nt) (a) In which exons might you find a frameshift mutation that inactivates the product of the Transcript A, but not that of Transcript B? (b) In which exons might you find a missense mutation that inactivates the product of the Transcript A, but not that of Transcript B? (c) In which exons might you find a nonsense mutation that does not inactivate the product of either transcript? (a) exon#2a: the mutation will cause a frameshift in the product of transcript A but not B. (b) exon#2a: A missense mutation in this exon could potentially inactivate the product of A, but not of B. (c) 4: if the nonsense mutation is toward the end of the gene, the gene product may still be functional. 2. (B level) (a) You are using the mutagen hydroxylamine which causes the replacement of a G-C base pair by an A-T base pair (G to A transition). Could hydroxylamine be used to induce an intragenic revertant of a nonsense mutation? (b) Could hydroxylamine cause a phenylalanine codon to be mutated to a tyrosine codon? (c) Starting with a codon for Glycine and allowing hydroxylamine to cause one substitution, codons for which four which amino acids (other than glycine) are the possible outcomes?
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