Nonsense mutation

Nonsense Mutation

A Nonsense Mutation (pronounced: non-sense myoo-tey-shuhn) is a type of mutation that results in a premature stop codon, or a 'nonsense codon' in the transcribed mRNA, causing a halt in protein synthesis.

Etymology

The term 'Nonsense Mutation' is derived from the concept that the mutation leads to the creation of a 'nonsense' codon. The word 'nonsense' is used because the mutation causes the codon to lose its original meaning, that is, its ability to code for a specific amino acid.

Types of Nonsense Mutations

There are three types of nonsense mutations, named after the three stop codons in the genetic code: UAA (Ochre), UAG (Amber), and UGA (Opal or Umber).

Ochre mutation: This is a point mutation in which a codon is changed to the 'UAA' stop codon.
Amber mutation: This is a point mutation in which a codon is changed to the 'UAG' stop codon.
Opal mutation: This is a point mutation in which a codon is changed to the 'UGA' stop codon.

Consequences of Nonsense Mutations

Nonsense mutations can have severe effects on the functionality of a protein. Since the mutation introduces a premature stop codon into the mRNA, the resulting protein is truncated. This can render the protein nonfunctional, leading to diseases such as Cystic fibrosis and Duchenne muscular dystrophy.

Related Terms

Point mutation: A type of mutation where one single nucleotide base is changed, inserted or deleted.
Frameshift mutation: A type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three.
Missense mutation: A type of mutation where a single nucleotide change results in a codon that codes for a different amino acid.