A fragment of a wild-type polypeptide is sequenced for seven amin...

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 polypeptide 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 . . .

Identify the mutation that produces each mutant polypeptide.

Accepted Answer

Hey, everyone. Let's take a look at this question together. The amino acid sequence of a fragment of wild type and mutant polypeptides is given below. We have our wild type polypeptide containing the following amino acid sequence. We have our mutant one which contains the following amino acid sequence. And we have our mutant two containing the following amino acid sequence, which of the following statements is correct regarding these sequences. And so we have to determine what type of mutation is seen in either of the two mutants. So first, let's determine the differences between our mutant one and our mutant two compared to that wild type polypeptide. And we can number our amino acids so that we can use the numbers to determine where the differences are in the sequences. And so looking at mutant one, we can see that we have a difference in that fourth amino acid or we have valine instead of glycine at the fourth position in our mutant one, which means that at the fourth position in mutant one, we have a single substitution. Since the fourth amino acid in our mutant one sequence is the only difference between mutant one and the wild type polypeptide sequence, which means that we have a miss sense mutation in mutant one, mutant two. We can see that amino acid one is the same as the wild type polypeptide. However, the rest of the amino acid sequence differs from that wild type polypeptide, which means that we have a shift in the reading frame since the whole sequence is different after that amino acid, which tells us that we have a frameshift mutation. So mutant one has a missense mutation and mutant two as a frameshift mutation. So looking at our answer choices, we can eliminate answer choice. A since mutant one and mutant two both do not have frameshift mutations and we can eliminate answer choice B because they don't both have miss sense mutations and we can eliminate answer choice. D since mutant two is the mutant with the frameshift mutation. And mutant one is the mutant with that missense mutation. Making answer choice C the correct answer since we are able to identify what type of mutation is found in mutant one, which is that missense mutation in mutant one. And we know that in mutant two we have a frameshift mutation. So answer choice C is the correct answer. I hope you found this video to be helpful. Thank you and goodbye.

Key Concepts

Amino Acids and Polypeptides

Types of Mutations

Comparative Sequence Analysis

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