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

Question

17. A fragment of a wild-type protein contains the following nine amino acids:

N...Trp-Trp-Trp-Met-Arg-Glu-Trp-Thr-Met...C

In four mutant versions of this protein, 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-Trp-Thr-Met...C

Mutant #3 N...Trp-Trp-Trp-Met-Arg-Glu-Trp-Met-Met...C

Mutant #4 N...Trp-Trp-Trp-Met-Arg-Glu-Met-Asp-Asp...C

Each mutant protein is the consequence of a single nucleotide change: either 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

Answer:

The given wildtype sequence of protein containing 9 amino acids is:

N...Trp-Trp-Trp-Met-Arg-Glu-Trp-Thr-Met...C

Different amino acids are coded by below mentioned triplet codons:

The wildtype sequence and 4 mutant protein sequences are:

There are two possible mRNA seqeuences for the given protein. The corresponding mRNA nucleotide sequence deduced from different mutated versions of the given protein is:

b) Classify each of the four mutations as a nonsense, missense, silent, or frameshift mutation.

Mutant #1: Non sense mutation (chain termination due to premature stop codon)

Mutant #2: Substitution mutation (Glutamic acid to Asparatic acid - conservative replacement)

Mutant #3: Missense mutation (Threonine to Methionine)

Mutant #4: Missense mutation

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