Point Mutation — Definition & Types

(Video) DNA Mutations Made Simple!

by Simple Science Answers

Mutation might seem like a scary word, but did you know it's just like changing one word in a sentence? Only, the sentence is DNA, and changing that one word can have a range of effects on an organism. This video explains different types of mutations using phrases and sentences.

There can be various effects depending on the type of mutation that happens.

Substitution mutations cause a single base pair to be exchanged for another. They can cause:

• Silent mutations: The substitution doesn't change the amino acid that the codon codes for.
• Missense: The substitution changes the codon so that it corresponds to a different amino acid than it should.
• Nonsense: The substitution changes the codon so that it signals an early stop of translation.

Insertion mutations happen when an extra base is inserted into a sequence. Similarly, a deletion mutation happens when a base is removed from the sequence. These changes can cause:

• Frameshift mutations: When a base is added or removed, the entire codon sequence following the mutation changes.

What Is a Point Mutation?

During either DNA replication or transcription, a nucleotide can get placed incorrectly. Enzymes like DNA polymerase or RNA polymerase can make these mistakes.

A point mutation is a gene mutation that changes a single nucleotide or just a few nucleotides in the DNA sequence. In other words, at least one nucleotide gets messed up. They show up at a single point in a DNA sequence.

These mutations can be base substitutions, deletions, or insertions.

• Substitution means that one base is exchanged for another. This is kinda like having a substitute teacher. The sub isn't your normal teacher, but they are still a teacher. A protein that is made with a substitution might still function normally, or it could be nonfunctional.
• Deletion is kinda self-explanatory. It happens when a base is deleted or, in other words, is just missing.
• Finally, insertion means an extra nucleotide is added.

These mutations can be good, bad, or have no effect on the protein. Occasionally, they can have serious evolutionary consequences. Point mutations alter codons—groupings of three nucleotides which correspond to different amino acids. What matters is, does the codon code for a different amino acid due to the mutation?

• A silent mutation is a mutation where the codon still corresponds to the same amino acid. The sequence of amino acids is not changed so the protein that gets made is the same as the wild type, or normal protein.
• A missense mutation changes the codon so that it codes for a different amino acid.
• Finally, a nonsense mutation causes protein creation to stop early, which makes a non-functioning protein.

Also, these changes can cause more significant mutations like frameshift mutations. These mutations result in the entire amino acid sequence of a protein shifting. Frameshifts happen when nucleotides get inserted or deleted. These mutations tend to have serious effects on protein functionality.

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

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

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

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

$\color{#8925AE}{\text{Codon}}$ : A group of three nucleobases that code 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

Why Do Mutations Happen?

Point mutations occur when there is a mistake at a single point in either a DNA or an RNA sequence.

These mutations, like most other mutations, occur when genetic material is being modified in the cell. During either DNA replication or transcription, a nucleotide can get placed incorrectly. Enzymes like DNA polymerase or RNA polymerase can make these mistakes. Polymerases have the ability to read and correct their own mistakes, but sometimes they still miss one.

There are three types of point mutations: deletions, insertions, and substitutions.

Deletions occur when a nucleotide is deleted. Insertions happen when a new nucleotide is inserted into the genome. Substitutions happen when a nucleotide is swapped for another nucleotide.

These mutations can cause one of several possible effects:

1. Silent mutation

2. Missense mutation

3. Nonsense mutation

4. Frameshift mutation