Answer to Question #129524 in Biochemistry for manahil

Question #129524
In a nutrient medium that lacks histidine, a thin layer of agar containing around 10^9 Salmonella typhimurium histidine auxotroph produces around 13 colonies over a two day incubation period at 37 degrees centigrade. How do these colonies arise in the absence of histidine? The experiment is repeated in the presence of 0.4 micrograms of 2-aminoanthracene. The number of colonies the number of colonies produced over 2 days exceeds 10,000. What does this indicate about 2- anthracene? what can you surmise about its carcinogenicity?
Expert's answer

Rarely, some of the histidine-requiring mutants impulsively they undergo back-mutation and recoup their capacity to synthesize histidine, and thus can grow in a medium lacking histidine. The observation that only 109 bacteria produce colonies; This is a clear indication that the rate of back-mutation is quite low. Therefore, addition of 0.4 micrograms of 2-aminoanthracene increases the rate of back-mutations more than 10,000-fold, thus indicating that 2-aminoanthracene is mutagenic. Approximately 90% of 300-fold are known to be carcinogens and at the same time mutagenic; therefore, these observations is a clear indication that 2-aminoanthracene is likely to be carcinogenic.

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