You are studying the tryptophan synthetase gene that Yanofsky also examined to d

Question

You are studying the tryptophan synthetase gene that Yanofsky also examined to determine the relationship between the nucleotide sequence and the amino acid sequence of the gene.

A) Yanofsky found a large number of mutations that affected the tryptophan synthetase gene. How did he find these mutations and why do you think he probably not recover missense mutations in a big stretch of the gene that encodes the part of the protein between amino acids 49 and 175?

B) You start by looking at the mutations that Yanofsky recovered. One of these mutations affected amino acid number 49 and changed it from Glutamic acid to Valine. If you took this mutant E. Coli line and exposed it to a mutagen that could potentially change bases, insert bases, or delete bases, what type of second mutation could you discover that would create a wild-type tryptophan synthetase gene and where would it be located?

C) Most of the mutations that Yanofsky recovered were missense mutations. However, Yanofsky also recovered a nonsense mutation that changed amino acid number 15 into a stop codon. This codon normally encodes Lysine. Does the recovery of this mutation support the hypothesis that this Lysine residue is critical in the function of the tryptophan synthetase protein? Why or why not?

Please answer these three parts, I will leave a thumbs up!

Explanation / Answer

A. Theoretically, each base in the DNA sequence has an equal probability of being mutated. However, mutations in non-essential regions such as non-coding regions are most common compared to mutations in coding regions. This is because mutations in coding regions may negatively affect the protein function and hence can not be tolerated and eliminated from the population. On the other hand, mutations in non-coding regions or non-essential regions of the coding sequence often do not cause any effect on a protein function. Hence these regions tend to accumulate mutations. In simple terms, conservation of a sequence is determined by its functional significance.

In the given scenario, most mutations are found in the region of 49-175. This shows that mutations in this region are tolerated and may not significantly affect protein function.

B. Glu ----> Val

It is a non-synonymous mutation. An acidic amino acid is changed to a non-polar amino acid. To reverse the effect of this mutation, another mutation must occur in the complementary region of the protein where a hydrophobic amino acid should be changed to an acidic amino acid (Glu or Asp)

C. No.

The location of a nonsense mutation does not indicate the functional significance of the amino acid position. Any base changes that generate UAA, UGA or UAG can lead to the production of truncated proteins.

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