Explain how mutations in the first and second positions in the triplet have bigger implications for protein production than in the third one.
The correct answer and explanation is:
Mutations in the first and second positions of a triplet codon have more significant implications for protein production than mutations in the third position due to the role these positions play in coding for specific amino acids.
- First Position: The first base in a triplet codon largely determines the identity of the amino acid encoded. For instance, the codons AUG and AUA both code for methionine and isoleucine, respectively, but a mutation in the first position can change one amino acid for another, which could disrupt the protein’s structure and function. Since the first position is crucial for defining the amino acid, any mutation here has a high potential for altering the protein’s properties or function.
- Second Position: The second position is critical because it contributes to the coding specificity for amino acids as well. For example, changing the second base in the codon GCU (which codes for alanine) to GCA would still code for alanine. However, altering this position can still have a dramatic effect depending on the amino acid it codes for. Mutations in the second position might change the amino acid to one with a vastly different chemical structure, affecting the protein’s folding and stability.
- Third Position (Wobble Position): The third position, often referred to as the wobble position, is generally less critical in determining the amino acid. This is due to the degeneracy of the genetic code, where multiple codons can code for the same amino acid. For instance, the codons GCU, GCC, GCA, and GCG all code for alanine. Mutations in the third position often do not lead to a change in the encoded amino acid, making these mutations less impactful for protein production.
In summary, mutations in the first and second positions are more likely to result in a change in the protein sequence, which could affect protein structure and function. The third position, due to codon redundancy, is less likely to change the amino acid and, consequently, has a lesser impact on protein production.