Base-substitution mutations often change the amino acid specified by a codon. For each of the amino acid changes listed, determine which ones can result from a one–base-pair substitution. For those that can result from a one–base-pair substitution, give the possible wild-type and mutant codons, listing multiple possibilities if there is more than one option. (Use either Figure 9.13 or the genetic code in Table A to help solve this problem).

Wild-type       Mutant
a. Ser               Ala
b. Cys              Ser
c. Pro               Glu
d. Lys               Stop
e. Met               His
f. Met                Ile

Key Concepts

Base-Substitution Mutations

Base-substitution mutations occur when one nucleotide in the DNA sequence is replaced by another. This can lead to changes in the corresponding mRNA codon, potentially altering the amino acid sequence of the resulting protein. Depending on the nature of the substitution, these mutations can be classified as silent, missense, or nonsense mutations, each having different effects on protein function.

Genetic Code and Codons

The genetic code is a set of rules that defines how sequences of nucleotides in DNA and RNA are translated into amino acids. Codons, which are sequences of three nucleotides, correspond to specific amino acids or stop signals during protein synthesis. Understanding the genetic code is essential for predicting how base substitutions can affect the amino acid sequence of proteins.

Wild-Type and Mutant Codons

Wild-type codons refer to the original, non-mutated sequences that code for specific amino acids, while mutant codons are the altered sequences resulting from mutations. Identifying the wild-type and mutant codons is crucial for determining the impact of base-substitution mutations on protein synthesis, as it allows for the comparison of the original and altered amino acid sequences.