Question

Below is the coding DNA sequence for a gene called tribble, including the wild-type and several mutant alleles. For each mutant allele, fully classify the mutation and its effect in the amino acid sequence. Wild-type 5'-ATGGCAACTACATATAGCACAGTTTGAACC-3' a. Mutant allele #1 5'-ATGGCAACTACATAAAGCACAGTTTGAACC-3' b. Mutant allele #2 5'-ATGGCAACTACATATAGCATAGTTTGAACC-3' c. Mutant allele #3 5'-ATGGCAACTACATACAGCACAGTTTGAACC-3' d. Which mutant allele is most likely to be a knockout and why?

Answer 1

Wildtype DNA sequence:

5'-ATGGCAACTACATATAGCACAGTTTGAACC-3

mRNA : 5'-AUGGCAACUACAUAUAGCACAGUUUGAACC-3'

polypeptide: Met-Ala-Thr-Thr-Tyr-Ser-Thr-Val

The provided DNA sequence is the coding strand of the DNA.

a.

Mutant 1:

DNA : 5'-ATGGCAACTACATAAAGCACAGTTTGAACC-3'

mRNA: 5'-AUGGCAACUACAUAAAGCACAGUUUGAACC-3'

polypeptide: Met-Ala-Thr-Thr

Because UAA is a stop codon.

This type of point mutation is known as Nonsense mutation. It leads to premature termination of translation.

b.

Mutant 2 :

DNA :5'-ATGGCAACTACATATAGCATAGTTTGAACC-3'

mRNA: 5'-AUGGCAACUACAUAUAGCAUAGUUUGAACC-3

polypeptide: Met-Ala-Thr-Thr-Tyr-Ser-Ile-Val

This type of mutation is called missense mutation. This mutation is a change in one DNA base pair that leads to substitution of one amino acid to another .

c.

Mutant 3 :

DNA : 5'-ATGGCAACTACATACAGCACAGTTTGAACC-3'

mRNA : 5'-AUGGCAACUACAUACAGCACAGUUUGAACC-3'

Polypeptide: Met-Ala-Thr-Thr-Tyr-Ser-Thr-Val

This is a silent mutation. The mutation have no affect on the polypeptide. The nucleotide substitution results to a change which codes for the same amino acid.

d.

Mutant 1 is most likely to knockout. Because it results into a truncated most probably nonfunctional protein.