A mutation in the TYR gene produces a protein that has a different structure tha

Question

A mutation in the TYR gene produces a protein that has a different structure than the original tyrosinase protein, thus creating a second TYR allele. This second TYR allele, produces a tyrosinase protein that results in less melanin second production. The phenotype associated with this allele is blond hair, blue eyes and light colored skin. Shown below is the same TYR gene DNA that was shown in problem 2. Two base pairs are highlighted in the DNA strand. Assume there is a mutation at each of these locations that changes the highlighted base to the to the nitrogenous base indicated above the arrow. Which of these mutations would produce the new TYR allele described, What type of mutation is this, and how do you know?

Explanation / Answer

If the given sequence is this I thinks so as the (screenshot is not readable clearly) of the DNA

5' TGT GCG GGC GCG GAG GAG GCA TGT TCT TGG TTT TAG CAA CGC CTG GAA CTG CGT AGC GGC CAT TGA CGT AAA CGA TGA CCA CAG 3'

This it DNA sequence, on Transcription it will form mRNA and latter which will be translated to protein. The mutation has occurred on the highlighted base pair region into “Adenine” a nitrogenous base pair. The base pairs are arranged into codons i.e. 3 nucleotide forms 1 codons and each codon codes for an Amino acid to form a polypeptide chain.

Now after mutation, the DNA base sequence is :-

5' TGT GCG GGC GCG GAG GAG GCA TGT TCT TGA TTT TAG AAA CGC CTG GAA CTG CGT AGC GGC CAT TGA CGT AAA CGA TGA CCA CAG 3'

The mRNA sequence for the mutated DNA strand is

5’ UGU GCG GGC GCG GAG GAG GCA UGU UCU UGA UUU UAG AAA CGC CUG GAA CUG CGU AGC GGC CAU UGA CGU AAA CGA UGA CCA CAG 3'’

The coding strand of DNA is same with the transcribed RNA except for Thymine (T) is replaced by Uracil (U)

The mutated codon 5’ UGA 3’ code for stop codon. And the synthesis of the protein will stop due to the mutated base in the DNA. This type of mutation is also called Lethal mutation as unwanted termination of protein synthesis occur. As the 1 mutation code for stop codon so, there is no significance for the 2 mutation as the protein synthesis is already stops.

      This type of mutation is called “Non sense mutation.” This is becuse the mutation which causes premature chain termination of the protein is Non Sense Mutation. In this case the peptide fragment which is formed would completely lose its biological activity and prevent the organism from surviving are known as Lethal Mutation.

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