A nonsense mutation is a DNA change that turns a codon for an amino acid into a stop signal, so protein-making stops too early. The result is usually a shortened protein that does not work properly.

Quick Scoop

A gene is normally read in groups of three DNA letters, called codons, and each codon usually tells the cell which amino acid to add next. In a nonsense mutation, one of those codons becomes a stop codon, such as UAA, UAG, or UGA, which tells translation to end early.

That early stop can leave the protein incomplete. In many cases, the protein is nonfunctional or only partly functional, though the exact effect depends on where the mutation occurs in the gene.

Simple example

Imagine a sentence like this:

  • “The cat ate the red fish.”
  • If a nonsense mutation creates a stop signal too soon, it becomes more like:
  • “The cat ate...”

The message cuts off before it is finished, which is why the protein often ends up too short to do its job.

How it differs

  • Missense mutation: changes one amino acid to another.
  • Silent mutation: changes a DNA letter but not the amino acid.
  • Nonsense mutation: changes an amino acid codon into a stop codon.

Why it matters

Nonsense mutations can cause genetic disease when an important protein is cut short. Some cells also destroy the faulty mRNA before it is translated, which can reduce protein production even more.

TL;DR

A nonsense mutation is a mutation that creates an early stop codon, causing a protein to be cut short and often not work properly.