Question

A polypeptide has the following amino acid sequence: Met-Ser-Pro-Arg-Leu-Glu-Gly The amino acid sequence of this polypeptide was determined in a series of mutants listed in parts a through e. For each mutant, indicate the type of mutation that occurred in the DNA (single-base substitution, insertion, deletion) and the phenotypic effect of the mutation (nonsense mutation, missense mutation, frameshift, etc.). a. Mutant 1: Met-Ser-Ser-Arg-Leu-Glu-Gly b. Mutant 2: Met-Ser-Pro c. Mutant 3: Met-Ser-Pro-Asp-Trp-Arg-Asp-Lys d. Mutant 4: Met-Ser-Pro-Glu-Gly e. Mutant 5: Met-Ser-Pro-Arg-Leu-Leu-Glu-Gly

Answer 1

The question pertains to different types of mutations observed in a polypeptide chain. Mutant 1 is due to a missense mutation, Mutant 2 seems to be a nonsense mutation, Mutant 3, 4, and 5 likely resulted from insertion and deletion mutations causing frameshifts.

Step-by-step explanation:

Each of the mutations outlined in the polypeptide sequences can be identified as follows:

1. Mutant 1: Met-Ser-Ser-Arg-Leu-Glu-Gly - This mutation is likely due to a single-base substitution in the DNA sequence coding for the third amino acid. The proline (Pro) has been replaced by a serine (Ser). This is referred to as a missense mutation as it results in a change in one amino acid in the sequence, potentially altering the structure and function of the polypeptide.
2. Mutant 2: Met-Ser-Pro - this truncated polypeptide sequence suggests that a nonsense mutation has occurred, where a base substitution has created a premature stop codon, causing translation to end early.
3. Mutant 3: Met-Ser-Pro-Asp-Trp-Arg-Asp-Lys - This sequence shows additional amino acids compared to the original sequence. This is likely the result of an insertion mutation, which causes a frameshift in the reading frame, altering the downstream amino acid sequence.
4. Mutant 4: Met-Ser-Pro-Glu-Gly - Here, a deletion mutation might have occurred. Arginine (Arg) and Leucine (Leu) are missing, suggesting that base pairs may have been removed in the DNA sequence, which also causes a frameshift.
5. Mutant 5: Met-Ser-Pro-Arg-Leu-Leu-Glu-Gly - In this case, an additional leucine (Leu) suggests a single-base insertion, causing a frameshift.

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