Final answer:
A nonsense mutation changes an amino acid-coding codon to a stop codon, leading to premature termination of the protein and frequently resulting in a nonfunctional protein.
Step-by-step explanation:
A mutation that changes an amino acid-coding codon into a stop codon is classified as a nonsense mutation. This type of mutation results in premature termination of the translational process, often leading to the production of a truncated, typically nonfunctional protein. Unlike a silent mutation, which does not change the amino acid and therefore has no effect on the protein, a nonsense mutation has a significant impact on the protein's function because it shortens the polypeptide chain and can render the protein inactive.