Introduction
A mutation is defined as an alteration in the sequence of DNA. There are various mutations, out of which point mutations are the most common. A point mutation is a type of mutation occurring in DNA or RNA (these are the cell's genetic material). The addition, deletion, or alteration of one single nucleotide base happens. DNA and RNA are made up of numerous nucleotides. The nitrogenous bases on the nucleotides are made up of five molecules: cytosine, guanine, adenine, thymine (in DNA), and uracil (in RNA). They are abbreviated as C, G, A, T, and U. There are specific sequences of nucleotides that encode all the information responsible for carrying out all the cell processes.
What Are The Types of Point Mutations?
The various types of point mutations have been mentioned below:
Substitution
A substitution mutation is the substitution of one base pair for another. It is further divided into the following three types of substitution mutations:
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Nonsense.
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Missense.
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Silent.
A nonsense mutation occurs due to substituting one nucleotide, which leads to the formation of a stop codon instead of a codon that codes for an amino acid. It is always present at the end of the mRNA sequence during protein production. However, if a substitution causes it to appear in a different place, it causes premature amino acid sequence termination and prevents the correct protein's production.
A missense mutation occurs due to the substitution of one nucleotide and the formation of a different codon. But, in this case, a stop codon is not formed; rather, a different amino acid is produced by the codon in the sequence of amino acids. A missense mutation is known to be conservative if the amino acid is formed because the mutation has the same properties as the actual amino acid that was supposed to be formed. If the amino has different structure and function properties, it is called non-conservative. A nucleotide substitution occurs in a silent mutation, but the same amino acid is produced. This can happen because multiple codons can code the same amino acid.
Insertion and Deletion
An insertion type of mutation happens due to adding an extra base pair to a sequence of bases, whereas a deletion type of mutation is the opposite of the insertion type. The deletion type occurs when a base pair gets deleted from a sequence. These two types of point mutations have been grouped as both can drastically affect the sequence of amino acids produced. AAA, the three-base codons can change with either the insertion or deletion of one or two bases. This phenomenon is known as a frameshift mutation. This leads to a complete change in the amino acids being produced, and thus, there can be a change in the structure and function of the resulting protein, making the resulting protein useless. Also, the sequence can shift if one base is deleted.
What Are The Examples Of Diseases Caused Due To Point Mutations?
Various diseases can be caused due to point mutations. The most common ones have been mentioned below:
Cystic Fibrosis
Cystic Fibrosis (CF) is a clinical condition characterized as a recessive inherited disorder that most commonly affects European people. Its prevalence in the United States is 1 in 3500 newborns, whereas 1 in 30 Caucasian Americans has been reported to be carriers. Various types of mutations may cause CF.
The common deletion of three nucleotides in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is out of these. This leads to the loss of the amino acid phenylalanine; thus, an incorrectly folded protein is formed. This condition is clinically associated with thick, sticky mucus in the lungs, which can cause difficulty breathing, infertility in a few individuals, salty sweat, and a decreased life expectancy of about 42 to 50 years in individuals belonging to developed countries.
Sickle-Cell Anemia
Sickle-cell anemia is another point mutation recessive disorder that is caused due to substitution of a single point in the gene that functions to create hemoglobin. Hemoglobin is the main carrier of oxygen in the blood and the body. Naturally, glutamic acid is present in the chain, but the substitution replaces glutamic acid with valine.
Thin sickle-shaped blood cells are formed when people have two copies of this mutation, and these modified cells are unable to carry oxygen efficiently sometimes. The prevalence is known to almost 80 percent of affected people in sub-Saharan Africa. In this region, if the individual is a carrier of sickle-cell anemia, they are not affected by malaria.
This mutation is also found in India and the Middle East. 1 in 500 African Americans is affected by this condition. Symptoms include anemia, chest pain, and obstruction of blood vessels. It can be managed with folic acid, bone marrow transplants, blood transfusions, and prescription drugs.
Tay-Sachs
Tay-Sachs disease is another type of recessive disorder caused by point mutations. It causes the deterioration of nerve cells with time, leading to worsening physical and mental functions. All children and adults can be affected. There is no treatment available.
Conclusion
Mutations are genetic alterations and can be of various types. Point mutation is the commonest type and can be further divided into various subtypes. It can cause structural as well as functional defects. Children and adults can both get affected. The diagnosis can be made during pregnancy; if not, it can be diagnosed later in life. Although there is no definite cure, the symptoms can be managed. You can consult a specialist online with the help of various online medical platforms to know more about this condition.