Substitution (DNA Mutation) — Definition & Examples

Substitution Mutations

A substitution mutation is when one nucleotide is swapped out for another. These types of mutations are the least dangerous of all the DNA mutations. That's because a single nucleotide change does not usually have a very large effect on the final protein.

There are three types of substitution mutations that all produce different effects.

Silent Mutation

A silent mutation is when a single base pair gets swapped out on the DNA, but the mutated RNA sequence produces the same amino acid. Codons are set up so that there are many ways to produce the same amino acid. If one nucleotide is changed, it will usually still produce the same amino acid.

Missense Mutation

A missense mutation is when a nucleotide gets changed, resulting in a different amino acid in the protein. This is the type of mutation that causes sickle cell anemia. Changing one nucleotide in the DNA sequence of a protein causes the blood cells to look like shriveled up little discs.

Nonsense Mutation

A nonsense mutation is the worst type of substitution mutation. This type of mutation occurs when a base change causes an early stop codon. This causes the protein to be too short and almost always results in a non-functioning protein.

Substitution Mutations

A substitution mutation occurs when specific bases (A, T, C or G) in a gene are swapped for different ones. This type of mutation doesn't cause a difference in the number of bases like insertion or deletion mutations do. Substitution mutations just switch out one or more bases for different ones.

Substitution mutations can cause many kinds of mutations. Some of these include nonsense, missense, and silent mutations. All of these depend on whether or not the new base codes for an amino acid different than the original.

What Are Substitution Mutations?

Substitution mutations are exactly what you would expect—a nucleobase is swapped with another in a DNA sequence.

This is kinda like having a substitute teacher. The sub isn't your normal teacher, but they are still a teacher. Substitution mutations normally only affect a single amino acid. They do not cause frameshift mutations.

Substitution mutations can be good, bad, or have no effect. They cause three specific types of point mutation: silent, missense, and nonsense mutations.

• A silent mutation is one where the function of the protein is not changed.
• A missense mutation codes for the wrong protein.
• A nonsense mutation causes protein creation to stop early. This makes a non-functioning protein.

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

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

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

$\color{#8925AE}{\text{Frameshift Mutation}}$ : A mutation that causes all the bases following it to be shifted

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

$\color{#8925AE}{\text{Insertion}}$ : An extra nucleotide is inserted into a DNA sequence

$\color{#8925AE}{\text{Substitution}}$ : A nucleotide is substituted for another nucleotide in a DNA sequence

$\color{#8925AE}{\text{Deletion}}$ : A nucleotide is deleted from a DNA sequence

(Video) Consequences of a Base Substitution Mutation

by Stephanie Castle

In this video, Stephanie Castle explains how a simple substitution mutation results in a common genetic disorder: sickle cell anemia. What happens is the bases GAG get changed to GTG. This changes the amino acid that is produced from glutamic acid to valine.

This change causes the hemoglobin in red blood cells to change shape. The sickle shape can be harmful for blood flow. It can cause serious side effects like stroke. This mutation also means that the red blood cells can't carry oxygen as well as they should be able to.