Final answer:
Point mutations can impair proteins if they lead to nonsense codons, nonsynonymous codons (missense mutations), or shifts in the reading frame (frameshift mutations), causing truncated or nonfunctional proteins.
Step-by-step explanation:
Point mutations can impair a protein if they result in the following:
- Nonsense codon
- Nonsynonymous codon (also known as a missense mutation)
- Shift in reading frame
A nonsense codon is a point mutation that changes a codon to a stop codon, resulting in a truncated and typically non-functional protein. Nonsynonymous codons, or missense mutations, change the amino acid sequence of a protein, which may affect the protein's function, especially if the substituted amino acid has different chemical properties or if it occurs in a crucial part of the protein. A shift in the reading frame, also known as a frameshift mutation, occurs when nucleotides are inserted or deleted from the DNA sequence in a number that is not a multiple of three, altering the triplet codon groupings. This can result in a completely different amino acid sequence downstream from the mutation and often leads to non-functional proteins, as new reading frames may include a stop codon before the end of the coding sequence.