A gene encodes a protein with the following amino acid...

A gene encodes a protein with the following amino acid sequence: $$\mathrm{Met-Trp-His-Arg-Ala-Ser-Phe}$$ A mutation occurs in the gene. The mutant protein has the following amino acid sequence: $$\mathrm{Met-Trp-His-Ser-Ala-Ser-Phe}$$ An intragenic suppressor mutation restores the amino acid sequence to that of the original protein: $$\mathrm{Met-Trp-His-Arg-Ala-Ser-Phe}$$ Give at least one example of base changes that could produce the original mutation and the intragenic suppressor. (Consult the genetic code in Figure 15.10.)

A gene encodes a protein with the following amino acid sequence:
$$\mathrm{Met-Trp-His-Arg-Ala-Ser-Phe}$$
A mutation occurs in the gene. The mutant protein has the following amino acid sequence:
$$\mathrm{Met-Trp-His-Ser-Ala-Ser-Phe}$$
An intragenic suppressor mutation restores the amino acid sequence to that of the original protein:
$$\mathrm{Met-Trp-His-Arg-Ala-Ser-Phe}$$
Give at least one example of base changes that could produce the original mutation and the intragenic suppressor. (Consult the genetic code in Figure 15.10.)

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Key Concepts

Genetic Code

The genetic code is the set of rules used by living cells to translate the nucleotide sequence of a gene into the amino acid sequence of a protein. It dictates which three-nucleotide codons correspond to which amino acids, and because the code is degenerate, multiple codons can specify the same amino acid.

Point Mutation

A point mutation is a change at a single nucleotide position in the DNA. Such mutations can alter a codon, leading to a change in the amino acid that is incorporated into a protein, as seen when an arginine codon is converted to a serine codon.

Missense Mutation

A missense mutation is a type of point mutation in which a single nucleotide change results in the substitution of one amino acid for another in the protein sequence. The example in the question involves a substitution that changes an arginine residue into a serine residue due to a codon change.

Intragenic Suppression

Intragenic suppression occurs when a second mutation within the same gene compensates for the effect of an initial mutation, restoring the original function or amino acid sequence. In the given problem, a second base change within the gene alters the mutated codon back to one coding for the original arginine residue, thereby rescuing the protein’s function.

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