MUTAGENS

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Mutagens are biological, physical or chemical agents that change the genetic materials (inclusive of DNA and RNA molecules) of an organism and thus increase the frequency of mutations above the natural background level. They are substances that change the genetic information of an organism, usually by changing DNA. Mutagens interact with nucleic acid molecules particularly the DNA to cause some alterations in them. This alteration in the DNA of a living organism can result to changes in the phenotype or physical appearance of the organism as well as changes in its genetic makeup.

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The two major causes of mutations or types of mutagens are (1) physical (irradiation) mutagens and (2) chemical mutagens. Physical mutagens or irradiation is exposure to radiation or ultraviolet (UV) light while chemical mutagens are chemicals that are capable of inducing mutation in a living organism. Benzene, vinyl chloride, formaldehyde, dioxane, and acryl amide are some typical examples of chemical mutagens that induce mutation in a living organism. Some metals can also act as mutagens and thus cause mutation in living systems. Table 1 shows the different types of physical, chemical and biological agents including metals that act as mutagens. 

Table 1. Types of mutagens

PHYSICAL MUTAGENSCHEMICAL MUTAGENSBIOLOGICAL MUTAGENSMETALS
    
X-rays (ionizing radiation)Reactive oxygen species (ROS) such as hydrogen peroxide and superoxide  Transposons (Transposons disrupt the functional elements of the gene when they are inserted into chromosomal DNA)  Arsenic
Gamma rays (ionizing radiation)Deaminating agents such as nitrous acid  Viruses (Viruses disrupt genetic function when inserted into the genome of a cell)  Chromium
Alpha rays (ionizing radiation)Alkylating agents such as nitrosamines and ethylnitrosourea  Bacteria (Some bacteria such as Helicobacter pylori cause inflammation during which oxidative species are produced, causing DNA damage and reducing efficiency of DNA repair systems, thereby increasing mutation)  Cadmium
Ultraviolet radiationsAromatic amines and amides  PrionsNickel
Radioactive decayAlkaloids from plants  
  —-
Cosmic raysBromine, benzene and sodium azide—-—-

Intercalating agents are mutagens that may insert between bases in DNA, causing frameshift mutation during DNA replication. Ethidium bromide (EtBr) is a typical example of an intercalating agent. Teratogens are other classes of mutagens which are known to cause harm to the foetus or embryo during pregnancy. They cause birth defects while the mother shows no signs of toxicity. Ethanol, mercury compounds, lead compounds, phenol, carbon disulfide, toluene and xylene are some examples of teratogens that can affect the foetus of a pregnant animal including humans. These compounds and/or chemicals are said to be teratogenic in nature because they affect the unborn foetus of a pregnant women.

Even some medications are teratogenic in nature, and thus pregnant or expectant mothers are advised not to resort to self-medication but always seek doctor’s prescription to be guided for antimicrobial therapy during pregnancy. The study of birth defects and malformations in the unborn/newborn due to mutations and other environmental or natural factors, and that may result to miscarriage or still birth is known as teratology. Minimizing exposure to mutagens in both the environment and at workplace is critical to the prevention of induced mutagenesis or mutation in a living host. Mutagens cause changes to the DNA that can affect the transcription and replication of the DNA, which in severe cases can lead to cell death.

The mutagen produces mutations in the DNA. Deleterious mutation can result in aberrant, impaired or loss of function for a particular gene, and accumulation of mutations may lead to cancer. Mutagens may also modify the DNA sequence of a gene. The changes in the nucleic acid sequences of an organism caused by mutations as aforementioned include:

Some mutagens can also change the number of chromosomes in the cell (a medical condition known as aneuploidy). A summary of the classification of mutagens is already shown in Table 1.

Further reading

Cooper G.M and Hausman R.E (2004). The cell: A Molecular Approach. Third edition. ASM Press.

Das H.K (2010). Textbook of Biotechnology. Fourth edition. Wiley edition. Wiley India Pvt, Ltd, New Delhi, India.

Davis J.M (2002). Basic Cell Culture, A Practical Approach. Oxford University Press, Oxford, UK. 

Mather J and Barnes D (1998). Animal cell culture methods, Methods in cell biology. 2rd eds, Academic press, San Diego.

Noguchi P (2003).  Risks and benefits of gene therapy.  N  Engl J Med, 348:193-194.

Sambrook, J., Russell, D.W. (2001). Molecular Cloning: a Laboratory Manual, 3rd edn. Cold Spring Harbor Laboratory Press, New York.

Tamarin Robert H (2002). Principles of Genetics. Seventh edition. Tata McGraw-Hill Publishing Co Ltd, Delhi.     

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