A fragment of a wild-type polypeptide is sequenced for seven amino acids. The sa

Question

A fragment of a wild-type polypeptide is sequenced for seven amino acids. The same polypeptide region is sequenced in four mutants.

Wild-type N-Thr-His-Ser-Gly-Leu-Lys-Ala-C

Mutant 1 N-Thr-His-Ser-Val-Leu-Lys-Ala-C

Mutant 2 N-Thr-His-Ser-C

Mutant 3 N-Thr-Thr-Leu-Asp-C

Mutant 4 N-Thr-Gln-Leu-Trp-Ile-Glu-Gly-C

a. Use the available information to characterize each mutant using the appropriate terms from this list: missense, nonsense, silent, frame-shift, transition, transversion.

b. Determine the wild-type mRNA sequence.

c. Identify the mutation that produces each mutant polypeptide.

Explanation / Answer

a. Wild-type N-Thr-His-Ser-Gly-Leu-Lys-Ala-C

Mutant 1 N-Thr-His-Ser-Val-Leu-Lys-Ala-C

There is mutation which changes Gly to Val

Codon for Gly is GGG and Val is GUG

Therefore there is a mutation which changes purine to pyrimidine.

So transversion mutation takes place.

ii. Wild-type N-Thr-His-Ser-Gly-Leu-Lys-Ala-C

    Mutant 2 N-Thr-His-Ser-C

In this case the Gly must be converted to a stop codon and then the truncated ppolypeptide formed.

GGG is converted to UGG.

This is called nonsense mutation.

iii. Wild-type N-Thr-His-Ser-Gly-Leu-Lys-Ala-C

      Mutant 3 N-Thr-Thr-Leu-Asp-C

ACU CAU AGU GGU CUU AAA GCU

ACU ACA CUU GAU

Frameshift mutation

iv. FRameshift mutation due to deletion.

b. mRNA sequence of wild type is

5’ACU CAU AGU GGU CUU AAA GCU3’

c. Described in part a

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