Difference Between Point Mutation and Frameshift Mutation

Main Difference – Point Mutation vs Frameshift Mutation

Point mutation and frameshift mutation are two types of gene mutations, which can occur due to errors in DNA replication and mutagens. Gene mutations are small scale mutations, which occur within the nucleotide sequence of a gene. The main difference between point mutation and frameshift mutation is that point mutation is an alteration of a single nucleotide in a gene whereas frameshift mutation involves one or more nucleotide changes, altering the open reading frame of a particular gene Point mutations are mainly nucleotide substitutions, which lead to silent, missense or nonsense mutations. Frameshift mutations occur by insertion or deletion of nucleotides.

Key Areas Covered

1. What is Point Mutation
      – Definition, Types, Features, Diseases Caused
2. What is Frameshift Mutation
      – Definition, Types, Features, Diseases Caused
3. What are the Similarities Between Point Mutation and Frameshift Mutation
      – Outline of Common Features
4. What is the Difference Between Point Mutation and Frameshift Mutation
      – Comparison of Key Differences

Key Terms: Deletions, Frameshift Mutation, Insertions, Missense Mutation, Nonsense Mutation, Point Mutation, Silent Mutation, Transition, Transversion

What is Point Mutation

An alteration of a single nucleotide in a gene is referred to as a point mutation. Point mutations arise from nucleotide substitutions. Purines and pyrimidines are the two types of nucleotides which make up the DNA. When a purine base is substituted into another purine base, the conversion is called a transition. When a purine base is substituted by a pyrimidine or vice versa, the conversion is called a transversion. There are three types of point mutations as silent mutations, missense mutations, and nonsense mutations. 

The three types of point mutations are shown in figure 1.

Figure 1: Point Mutations

Silent Mutations

In silent mutations, though a single base pair has changed in a particular codon, the same amino acid is coded by the altered codon as well. This can happen due to the degeneracy of the genetic code. That means there can be several codons in the genetic code to represent a particular amino acid. Therefore, no phenotypic change in the organism occurs although the genotype of the organism has changed.

Missense Mutations

In missense mutations, once the alteration occurs in a particular codon by a nucleotide substitution, the codon is altered in such a way to code a different amino acid. Sometimes, the chemical properties of the substituted amino acid could be same as the original amino acid. In this situation, no phenotypic change is observed. However, if the substituted amino acid consists of different properties, the mutated protein can be either non-functional or sometimes lethal.

Nonsense Mutations

In nonsense mutations, the alteration of a nucleotide in a particular codon may introduce a stop codon to the gene. This stops the translation of the protein at halfway of the complete protein. The substituted protein is non-functional and shortened in length. These type of non-functional proteins are chopped off later by cellular mechanisms.

What is Frameshift Mutation

Mutations that alter the open reading frame of a gene are referred to as frameshift mutations. Frameshift mutations can occur in two ways; insertion of bases and deletion of bases. Insertion of one or more base pairs into the nucleotide sequence of a gene shifts the downstream bases to the right. Deletion of bases shifts the downstream bases to the left. Both insertions and deletions cause alteration of the open reading frame of a particular gene. Typically, DNA is coded in such a way to introduce stop codons if a frameshift occurs by a mutation. This will save cellular energy which may be wasted to produce a non-functional protein. 

Figure 2: Frameshift Mutation

Similarities Between Point Mutation and Frameshift Mutation

• Both point mutation and frameshift mutation are two types of gene mutations.
• Both point mutation and frameshift mutation are involved in the production of non-functional proteins.
• In order to maintain a point mutation or frameshift mutation, each alteration should be replicated

Difference Between Point Mutation and Frameshift Mutation

Definition

Point Mutation:  An alteration of a single nucleotide in a gene is referred to as a point mutation.

Frameshift Mutation: Mutations that alter the open reading frame of a gene are referred to as frameshift mutations:

Number of Base Pairs

Point Mutation: Point mutations involve single nucleotide alterations

Frameshift Mutation: Frameshift mutations involve alterations in several nucleotides.

Types

Point Mutation: Point mutations occur due to substitutions.

Frameshift Mutation: Frameshift mutations occur due to insertions or deletions of nucleotides.

Influence

Point Mutation: Point mutations can be silent, missense or nonsense.

Frameshift Mutation: Frameshift mutations cause alterations of the open reading frame of a protein.

Significance

Point Mutation: Point mutations alter the structure of a gene.

Frameshift Mutation: Frameshift mutations alter the number of nucleotides in a gene.

Diseases

Point Mutation: Sickle cell anemia is caused by point mutations.

Frameshift Mutation: Tay-Sachs disease is caused by frameshift mutations.

Conclusion

Point mutation and frameshift mutation are two types of gene mutations, which occur in the nucleotide sequence of a gene. Point mutation is an alteration of a single nucleotide whereas frameshift mutation is one or more nucleotide changes, altering the open reading frame of a particular gene. Therefore, the main difference between point mutation and frameshift mutation is their effect on the production of a functional protein. 

Reference:

1.”What is a Mutation?”. utminers.utep.edu. N.p., n.d. Web. Available here. 30 July 2017. 

Image Courtesy:

1. “Frameshift deletion (13062713935)” By Genomics Education Programme – Frameshift deletion (CC BY 2.0) via Commons Wikimedia

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