Why can changes in a gene affect the function of a protein?

Changes in a gene—known as mutations—can alter the function of a protein because the sequence of nucleotides in DNA dictates the specific order of amino acids used to build that protein.12

When a mutation occurs, it can disrupt this process in several ways:

• Amino Acid Substitution: A missense mutation may replace one amino acid with another. If the new amino acid has different properties, it can alter the protein's structure or impair its ability to function, such as by disabling an enzyme at its active site.43
• Premature Termination: A nonsense mutation introduces a stop codon prematurely, leading to an incomplete protein that typically loses all function.43
• Reading Frame Shifts: Frameshift mutations, caused by the insertion or deletion of nucleotides, shift the reading frame of the genetic code. This alters all downstream codons, resulting in a protein with a sequence of meaningless amino acids.43
• Regulatory Interference: Mutations in promoter or regulatory regions can inhibit or mistime protein production, while mutations affecting intron splicing can result in nonfunctional proteins containing extra, meaningless sequences.4