A missense mutation is an alteration in the DNA that results in a different amino acid being incorporated into the primary structure of a protein. At a molecular level, DNA consists of two strands built from four nucleotides called adenine, cytosine, guanine, and thymine (i.e., A, C, G, T, respectively). To produce a protein, DNA must first be transformed into messenger RNA, or mRNA, by an enzyme called RNA polymerase. During translation, specialized proteins called ribosomes read the mRNA in groups of three nucleotides, called codons. Each codon either encodes a specific amino acid or functions as a stop codon, signaling the end of protein synthesis. The ribosome matches these codons with the corresponding amino acids to assemble the final protein.
Missense mutations occur when a single nucleotide base in a DNA sequence is swapped for another one, resulting in a different codon and, therefore, a different amino acid. These mutations are quite common, and, in most cases, they don’t affect the overall shape and function of the protein. However, when the amino acid substitution involves two amino acids with very different chemical properties, missense mutations can lead to significant changes in protein function. In such cases, they are known as nonconservative missense mutations.
