Why can a nonsense mutation cause a protein to stop being made too early?

A nonsense mutation causes a protein to be truncated because it introduces a premature stop signal into the genetic sequence.

During protein synthesis, the cellular machinery reads messenger RNA in three-nucleotide sequences called codons. While most codons specify an amino acid, three specific sequences—UAG, UAA, and UGA—act as termination signals that instruct the ribosome to stop translation and release the newly formed protein chain.12

A nonsense mutation is a type of point mutation that alters a single base pair in the DNA, resulting in one of these stop codons appearing in a position where it does not belong. When the ribosome encounters this unexpected stop signal, it terminates the assembly of the protein prematurely. This typically results in an incomplete, nonfunctional protein product.3