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Understanding Mutagens responsible for Mutation
Background: Mutagens cause changes (mutations) in the genetic material of cells. A mutation can be the result of different events. Errors made during replication, repair, or recombination can all lead to point or frameshift mutations. Mutations resulting from such errors are spontaneous mutations. A mutation can also result from the action of physical and chemical agents known as mutagens.

Gene, the basic unit of a DNA acts as genetic messenger. Genes are responsible for synthesis of proteins, the important biomolecule responsible for carrying out all cellular function. Any alteration in the gene structure results in the alteration of the genetic message. This change in structure of a gene is called as mutation and mutation can be either spontaneous or induced mutation.

Spontaneous mutation occurs as a result of failure in the process of DNA duplication, which involves steps like DNA helicase induced DNA replication where the DNA strands are separated and action of DNA polymerase in creating copies of replicated DNA strands resulting in formation of two double stranded DNAs. Misfunction of DNA polymerase contributes to mutation. Generally, spontaneous mutations are reversed by the repair mechanism using DNA repair proteins.

Induced mutation occurs as a result of exposure to various external factors like radiation, drugs, virus, pesticides, asbestos, alcohol and smoking. The agents or molecules which are responsible for mutation are called as mutagens. The various factors causing mutation are discussed in detail.

Radiation: There are two types of radiation called as ionizing radiation and non ionizing radiation. The alpha rays, beta rays, gamma rays, X-rays, cosmic rays and a part of UV rays are classified under ionizing radiation. Whereas, the non ionizing radiation includes microwaves, radio waves, infra red light and visible light. Nuclear reactors, nuclear fission and nuclear fusion reactions, radioactive elements, sun and particle accelerators are some of the sources of ionizing radiation.

Ionizing radiations have wide application in the field of medicine and agriculture. X-rays are widely used in the radiology section in hospitals and there are various radiation therapies available. In agriculture radiations are used as a pest control measure, where the male numbers are sterilized by exposing to radiation which restricts the increase in pest population. Also radiations are used in the food industry to sterilize the food and packing materials. Besides these benefits, exposure to ionizing radiation results in gene mutation. The type of radiation, the intensity of radiation and the length of exposure to radiation are the factors to be considered while analyzing mutation due to radiation. Ionizing radiation deforms the structure of the DNA by acting on the bonds through which the bases are connected. Whereas mutation is not observed when exposed to non-ionizing radiation except for some effects on body due to the thermal energy produced.

Virus: Viruses are also potential mutagens. In instances of some acquired viral infections, the virus attaches to the cell, transfer its genetic material into the cell thus altering the original gene, causing mutation. SV40 virus and Human Papilloma virus are examples of viral mutagens. Based on the type of genetic material whether DNA or RNA, a virus carries it is called as DNA virus and RNA virus accordingly. Examples of DNA viral mutagens are Hepatitis B virus and Human herpes virus. Hepatitis C virus is an example of RNA virus which causes cancer in liver by suppressing the activity of the tumor suppressing gene.

Asbestos: The common material used widely is identified as mutagen. Exposure to asbestos mutates p53 gene, thus altering the tumor suppressing role of the gene, causing lung cancer.

Pesticides: The exposure to pesticides, either by handling the pesticide or inhaling the pesticide causes gene mutation. The growth abnormalities observed in the children born to pregnant women exposed to the pesticide ‘Endosulfan’ is a good example. As a result many pesticides were banned by the government which includes Endosulfan and DDT.

Smoking and Drinking: Tobacco and alcohol also plays the role of mutagens when consumed in excess. Mutation caused by chain smoking is similar to that of the exposure to asbestos. Consumption of alcohol in excess causes sperm cell mutation contributing to genetic defects in the offspring.

All the mutations are not inheritable. It depends on the type of cell mutated, either a gene in the somatic cell or the germ cell. The mutation of genes in egg and sperm cell alters the trait of the offspring. Whereas the mutation of a gene due to exposure to UV rays from sun causes skin cancer only in the exposed individual and it is not passed on to next generation. Mutation due to the above discussed factors can be controlled by adopting various preventive measures suitable for the type of mutagen.
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Understanding Mutagens responsible for Mutation - by priyasaravanan_1406 - 10-05-2012, 10:11 PM
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