Comstock/Comstock/Getty Images
A mutation at the molecular level refers to any addition, deletion, or substitution of nucleotide bases in DNA. DNA consists of four nucleotides—adenine (A), cytosine (C), guanine (G), and thymine (T). The precise sequence of these bases encodes the instructions for amino acids, the building blocks of proteins. Maintaining the correct base order is essential for producing functional proteins; mutations can range from benign to disease‑causing.
A silent, or synonymous, mutation changes a single nucleotide but still encodes the same amino acid. Because the genetic code is degenerate—multiple codons can specify the same amino acid—such substitutions typically have no detectable effect on the resulting protein.
A missense mutation replaces one nucleotide with another, producing a codon that specifies a different amino acid. The impact depends on the properties of the substituted amino acid; conservative changes may be tolerated, whereas non‑conservative substitutions can alter protein structure or function and are implicated in various disorders, including cancer.
A nonsense mutation introduces a premature stop codon (UAA, UAG, or UGA). Translation halts early, yielding a truncated protein that is usually nonfunctional. Such mutations are a major cause of inherited diseases and contribute to oncogenesis.
Insertions or deletions not in multiples of three nucleotides shift the reading frame. The downstream codons are read incorrectly, producing a completely different amino‑acid sequence and often a premature stop codon. Frameshift mutations typically result in dysfunctional or truncated proteins.
