A mutation is a change in the DNA found within a living organism’s cell, as defined by genetics. Mutations can be caused by a variety of factors, including the organism’s age and external factors such as the sun. They can even occur as a result of errors that occur during the copying of DNA in preparation for the creation of a new cell. The location of the mutation and the amount of DNA involved determine the extent of the mutation’s impact on the cell. When one nucleotide in a DNA strand is replaced with another, this is known as a point mutation.
Adenine (A), thymine (T), guanine (G), and cystine (C) are the four nucleotides that make up DNA (C). The gene found within that strand of DNA is determined by the order of these nucleotides. Most genes have multiple variants, which are caused by small changes in nucleotide sequence. The significance of a change is determined by where it occurs; while changes in some strands produce minor differences, others can result in defects and diseases.
Genes serve as the blueprints for all of a cell’s proteins. Changing the nucleotides can result in the production of a similar protein, a different protein, or no protein at all. While a point mutation is defined as a change in a single nucleotide, it is not limited to minor variations. The location of a point mutation in a gene sequence can have a significant impact on the protein that is produced.
One way to classify point mutations is to look at which nucleotide is being replaced by which other. Purines and pyrimidines are the two types of nucleotides, based on their chemical makeup and shape. Purines are adenine and guanine, while pyrimidines are thymine and cytosine. When a purine replaces a purine or a pyrimidine replaces a pyrimidine, a transition point mutation occurs. A point mutation is called a transversion mutation when a purine replaces a pyrimidine or vice versa.
Another way to categorize point mutations is by the impact they have on the cell’s function. When making a protein, the nucleotides are grouped into codons, which are made up of three nucleotides. Within a protein chain, each codon codes for an amino acid. A single nucleotide change within a codon can have a significant impact on the protein that results.
In some cases, a point mutation converts a codon to a stop code, resulting in a protein that is much smaller than it should be because the rest of the sequence is missing after the mutation. A nonsense mutation is a specific type of point mutation. Missense mutations happen when a nucleotide is substituted, resulting in a codon for a different amino acid. Because amino acids can have multiple codons, a silent mutation occurs when the change causes the same amino acid to be produced. When a substitution results in a different amino acid being coded for within a protein, but this change has no effect on the protein’s function, it is referred to as a silent point mutation.