A glycine residue is in position 210 of the tryptophan synthetase enzyme of wild-type E. coli. If the codon specifying glycine is GGA, how many single-base substitutions will result in an amino acid substitution at position 210? What are they? How many will result if the wild-type codon is GGU?

Key Concepts

Codons and Amino Acids

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during protein synthesis. Each amino acid is encoded by one or more codons, which are derived from the genetic code. For example, the codon GGA specifies glycine, and understanding how changes in the nucleotide sequence can lead to different codons is essential for predicting amino acid substitutions.

Single-Base Substitution Mutations

Single-base substitution mutations occur when one nucleotide in the DNA sequence is replaced by another. This type of mutation can lead to changes in the corresponding mRNA codon, potentially resulting in a different amino acid being incorporated into a protein. The impact of these mutations depends on the specific codon changes and the resulting amino acids.

Genetic Code Degeneracy

The genetic code is described as degenerate because multiple codons can encode the same amino acid. For instance, glycine can be specified by GGA, GGU, GGC, and GGG. This redundancy means that some single-base substitutions may not lead to an amino acid change, while others will, making it important to analyze the specific codons involved when considering mutations.