Nonsense Mutation — Definition & Examples

Definition of Nonsense Mutation

A nonsense mutation happens when a stop codon (or nonsense codon) is created in the wrong location. A trick to remember this is the phrase "Stop the nonsense!"

Stop codons (premature termination codons) are kinda like the period at the end of a sentence. They do not code for any amino acid; rather, they signal the end of protein synthesis.

There are three stop codons: TAA, TAG, and TGA for DNA, and UAA, UAG, and UGA for RNA. Notice that they are the same, just with thymine for DNA and uracil for RNA.

These mutations cause protein synthesis to end early. This creates nonfunctional or truncated proteins (ones that are missing certain parts).

You can think of this like a sentence not being finished, like in the case of—

Yeah, like that.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Mutation}}$ : A change in genetic code

$\color{#8925AE}{\text{Point Mutation}}$ : A potentially harmful mutation that occurs at a single point in the DNA sequence

$\color{#8925AE}{\text{Frameshift}}$ : A mutation that causes the reading frame (groups of three nucleobases) to be shifted

$\color{#8925AE}{\text{Codon}}$ : A group of three nucleobases that codes for a specific amino acid

$\color{#8925AE}{\text{Missense}}$ : A substitution mutation that codes for an incorrect nucleobase

$\color{#8925AE}{\text{Nonsense}}$ : A mutation that causes a stop codon to appear in an incorrect location which prevents the protein from being completed

$\color{#8925AE}{\text{Silent}}$ : A mutation that has no effect on the final protein product

What Are Nonsense Mutations?

This is another type of point mutation where a base pair change codes for a premature stop codon. These mutations result in a protein that is far too short or not viable at all.

(Video) Nonsense Mutation

by Shomu's Biology

If a mutation in the genetic code causes the ribosome to stop translating the mRNA sequence before it's supposed to, it is called a nonsense mutation. This causes a premature termination of protein synthesis.

The three stop codons are UAA, UAG, and UGA.