17.A fragment of a wild-type protein contains the following nine amino aclds N..

Question

17.A fragment of a wild-type protein contains the following nine amino aclds N...Trp-Trp-Trp-Met-Arg-Glu-Trp-Thr-Met.c In four mutant versions of this proteln, this same fragment contains the following amino acids: Mutant #1 N Trp-Trp-Trp-Met-C Mutant #2 N. Trp-Trp-Trp-Met-Arg-Asp-Tp-Thr-Met Mutant #3 N Trp-Trp-Trp-Met-Arg-Glu-Trp Met-Met Mutant #4 N. Trp-Trp-Trp-Met-Arg-Glu-Met-Asp-Asp c C C Each mutant protein is the consequence of a single nucleotide change: elther a substitution of one nucleotide, an insertion of one nucleotide, or a deletion of one nucleotide a) Using the information provided by the mutant protein sequences (and the codon table in your textbook), deduce the sequence of the wild-type mRNA encoding the nine amino acids in the wild-type protein. If there is more than one possible nucleotide, list all possibilities. b) Classify each of the four mutations as a nonsense, missense, silent, or frameshift mutation. Mutant # 1: Mutant #2: Mutant #3: Mutant #4:

Explanation / Answer

17. Given protein sequence: N'-Trp-Trp-Trp-Met-Arg-Glu-Trp-Thr-Met-C'

WT mRNA sequence: UGG UGG UGG AUG CGA GAA UGG ACG AUG

Number codons for Trp = 1

Number codons for Met = 1

Number codons for Arg = 6

Number codons for Glu = 2

Number codons for Thr = 4

Total number of possible mRNA sequences = 1 X 1 X 6 X 2 X 4 = 48

Mutant-1 mRNA sequence: UGG UGG UGG AUG UGA GAA UGG ACG AUG

It is a nonsense mutation.

Mutant-2 mRNA sequence: UGG UGG UGG AUG CGA GAU UGG ACG AUG

It is a missense mutation.

Mutant-3 mRNA sequence: UGG UGG UGG AUG CGA GAA UGG AUG AUG

It is a missense mutation.

Mutant-4 mRNA sequence: UGG UGG UGG AUG CGA GAA AUG GAC GAU G

It is a frameshift mutation.

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