Genetic mutations are permanent changes in the building blocks of a gene. These changes often help living things evolve by creating new traits that can be useful for survival. But sometimes, mutations can cause problems and lead to health issues or diseases.
Where a mutation happens and how it changes important proteins can affect health in different ways. Mutations can be grouped by how they change the DNA or the protein made from it. Here are the common types:
1. Insertion | Adding extra pieces of DNA. |
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2. Deletion | Losing pieces of DNA. |
3. Substitution | One unit of DNA is replaced by a different one |
4. Deletion-Insertion | Some DNA is removed, and new DNA is added in its place. |
5. Inversion | A section of DNA is flipped around. |
6. Duplication | A part of DNA is copied one or more times. |
7. Repeat Expansion | Certain DNA sequences get repeated more times than usual. |
8. Frameshift | Insertions or deletions that change the way the DNA is read, often messing up the whole protein |
Depending on how this change affects the protein made from the gene, substitutions are divided into two types:
- Missense mutation
- Nonsense mutation
Missense mutation
- Missense mutation is defined as a type of mutation where substitution of different amino acid takes place into the amino acid sequence that results into nucleotide change.
- Missense mutation is also known as non-synonymous substitution.
- Stop codon is not generated in missense mutation for terminating the sequence of amino acid synthesis.
- In missense mutation if new amino acid consists of similar features as in the original amino acid, the missense mutation is called as conservative mutation.
- If new amino acid has different properties as compared to the original one, then this type of missense mutation is known as non-conservative mutation.
- The mutated protiens can become non functional or else can have different functions compared to original protein.
Nonsense mutation
- Nonsense mutation is defined as a type of mutation where a premature stop codon is introduced into mRNA sequence that results into a nucleotide change.
- There are three stop codons in the DNA sequence namely TAG, TAA and TGA.
- These three codons are then transcribed into mRNA sequence that produces three different types of nonsense mutations known as UAG(amber mutations), UAA(ochre mutations) and UGA(umber mutations).
- By the insertion or deletion of a single nucleotide in the nucleotide sequence these three different mutations can also emerge.
- In mRNA the remaining codons that are beyond the stop codon will not be translated and it leads to premature chain termination.
Do You Know ?
Missense mutations can sometimes be beneficial by creating new protein functions that help organisms adapt to changing environments.
Nonsense mutations often trigger a cellular quality control process called nonsense-mediated decay, which helps prevent the production of faulty proteins by destroying the abnormal mRNA.
Difference between Missense and Nonsense Mutation
Below are the differences between missense and nonsense mutation:
Parameter | Missense Mutation | Nonsense Mutation |
|---|---|---|
Definition | A missense mutation is defined as a type of mutation where the substitution of different amino acids takes place into the amino acid sequence that results in nucleotide change. | Nonsense mutation is defined as a type of mutation where a premature stop codon is introduced into the mRNA sequence that results in a nucleotide change. |
The type of codon introduced | Missense mutation introduces a distinct codon. | Nonsense mutation introduces a stop codon at the site of mutation. |
Results into | Missense mutation results in a distinct amino acid. | Nonsense mutation results in the termination of a premature chain. |
Type of protein resulted | Missense mutation results into an incomplete protein. | Nonsense mutation results into a conserved protein. |
Type of proteins produced | Missense mutation produces proteins that are non-functional. | Nonsense mutation produces proteins that are functional, non-functional or can have a distinct function from the original proteins. |
Final product | Missense mutation results in a different amino acid sequence as a final product. | Nonsense mutation results in a unfinished or short protein as a final product. |
Leads to disorders | Missense mutation leads to genetic disorder such as Duchenne Muscular Dystrophy(DMD), Dravet syndrome and Hurler syndrome. | Nonsense mutation leads to sickle-cell disease, Mediated Amyotrophic Lateral Sclerosis(ALS) and Epidermolysis bullosa. |
Conclusion
A missense mutation alters a codon so that it codes for a different amino acid, which can change the protein’s function or make it non-functional. On the other hand, a nonsense mutation changes a codon into a stop signal, causing the protein to be cut short and usually lose its function.