Ames test is used to determine? (GATE BT 2010)
|(a) The Mutagenicity of a chemical||(b) Carcinogenicity of a chemical|
|(c) Both Mutagenicity and Carcinogenicity||(d) Toxicity of a chemical|
Correct Answer is : (A) The Mutagenicity of a chemical
Ames test was developed in 1970‟s by a Biochemistry professor, Bruce Ames (hence the name), as a fast and sensitive assay to index the ability of a chemical compound or mixture to induce mutations in DNA.
About the Ames test:
Ames test is cheap, fast and ethical, as it doesn’t use any human/animal model to test for the mutagenicity of a chemical. Ames test rather relies on monitoring the induction of mutations in “bacteria” using the chemical.
In a typical Ames test, mutant strains of the bacteria Salmonella tymphimurium (S. typhimurium) containing a mutant gene (encoding an enzyme used to synthesize the amino acid histidine) are used. These strains thus can’t synthesize Histidine and are given a genotype: his–
Histidine is crucial for the growth of bacteria, as it’s required for the synthesis of several proteins. In the event of absence of histidine production, these bacteria will slowly die in the media they are grown, once the histidine present in the medium depletes.
Mutation like these are secondary mutations that occur at a low spontaneous (natural/uninduced) rate. Those who revert back to his+ are termed as revertants and can now grow just fine in media lacking histidine.
The assay thus involves plating his– S.typhimurium onto media with trace amounts histidine and adding chemicals to the test plate, which are supposed to be tested for mutagenicity. A control plate lacking any chemical would indicate the rate of natural reversion. The number of colonies growing on the test plate would serve as the index of reversion efficacy. An ideal test would involve the use of various concentrations of the chemical to generate a dose-response curve.
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