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Understanding Mutagens responsible for Mutation
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Gen means birth or origin, as in the book of Genesis, which explains the origin of the Earth; "Muta" means change; "terato" means monster; and "carcino" means crab. Thus, all three "gens"-are physical or chemical agents that cause or originate malformations.

Mutagens cause changes (mutations) in the genetic material of cells. Teratogens cause irreversible, deleterious structural malformations in fetuses. Some congenital malformations are so severe they result in grossly deformed fetuses. Carcinogens cause cancerous tumors with a characteristically crablike appearance.

Mutagens, teratogens and carcinogens are similar in that each causes some form of mutation. Congenital malformations can be caused by mutations, which may occur in the parent germ cell (sperm or ovum), in the resulting embryo (mutagenic effect), or in some cells of a fetus after development has begun (teratogenic effect). Mutations in somatic (body) cells can cause certain cancers (carcinogenic effect). One hypothesis for determining the etiology of chemically induced cancer involves the concept of somatic mutation, which is based on the fact that several chemicals capable of causing cancer in animals also are capable of causing mutations in microorganisms.

Mutagens. The most significant mutagenic event is transmission of heritable effects through germ cells to the next generation. Germ cells are comprised of complex structures called chromosomes. Chromosomes are composed of molecules of deoxyribonucleic acid (DNA) and are contained in cell nuclei. A gene is the smallest unit of a germ cell considered to carry a genetic message; one gene exists for each characteristic. Genes are linked together in long chains to form chromosomes.

When sufficient evidence establishes a causal connection between human exposure to a chemical and heritable genetic effects, the substance is classified as a mutagen. Mutations may occur either in somatic (body) cells or germ (reproductive) cells. Somatic mutations are inherited by other somatic cells formed from a changed cell, but they are not inherited by offspring of organisms in which a somatic mutation resides. Chemicals that can produce this type of mutation are referred to as "genotoxic." Although these agents do not damage future generations, they may initiate a biochemical rampage in cells of an affected organism. The result is a cancerous growth.

Recent studies show chemicals can cause mutations by generating rapid cell division, or mitogenesis. "A dividing cell is much more at risk of mutating," explains Bruce Ames, a research scientist at the University of California, Berkeley. "These mutations can transform normal cells into cancer cells." Non-genotoxic, or epigenetic, chemicals generally cause mutations only when administered in enormous doses. The best example is saccharin.

Teratogens. Teratogens are agents that cause abnormalities in developing organisms in the womb. When a fetal abnormality is manifested in progeny, the infant is born with a congenital defect, anomaly or malformation. Congenital abnormalities also may result from other factors. Human congenital abnormalities may stem from diseases mothers may have during the first trimester of pregnancy, particularly such viral diseases as German measles (rubella).

Carcinogens. Carcinogens can cause malignant tumors. However, a distinction between benign and malignant tumors is not always possible. Nevertheless, the mark of carcinogenicity is an increase in malignant tumors. For a chemical to be considered a human carcinogen under expected conditions of exposure, it also must be genotoxic.
Studies show that up to 90 percent of all mutagens are carcinogens. The theory that mutation sets the stage for cancer development is based on the fact that many mutagenic physical and chemical agents also are carcinogenic. Mutations giving rise to cancer usually occur in somatic cells. If a change caused by such mutations is minor, it probably never will be discovered. However, if there is a major change, the cell may die.
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RE: Understanding Mutagens responsible for Mutation - by rosaclinic - 10-07-2012, 12:46 AM
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