Which class of mutations would result in a significant alteration of a protein?

A missense mutation leads to a significant alteration of a protein because it involves a change in a single nucleotide that results in the substitution of one amino acid for another in the protein sequence. This alteration can affect the protein's structure and function, potentially altering its activity, stability, or interactions with other molecules. Since amino acids have different properties, even a single change can significantly influence the three-dimensional conformation of the protein, ultimately impacting its role in biological processes.

In contrast, a silent mutation does not change the amino acid sequence of the protein, meaning there is typically no effect on the protein's function. A nonsense mutation introduces a premature stop codon, resulting in a truncated protein that may be nonfunctional, though not all nonsense mutations will lead to significant changes depending on the position of the stop codon. While a point mutation can refer to a single nucleotide change, it encompasses silent, missense, and nonsense mutations. Therefore, not all point mutations will result in significant alterations to proteins, but missense mutations specifically result in functional variations.