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THE CARNIVAL OF THE AMES TEST

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The Ames test is a biological test widely utilizzatoper determnare if a compound is carcinogenic (capable of induerre tumor formation). The test developed by Bruce Ames is based on the ability of a mutant to be carcinogenic, inducing a revertant mutation in an organism that will be used in the experiment.

The test is performed using mutant strains of Salmonella thiphymurium changed. The mutation prevents them to be able to synthesize the amino acid histidine . Histidine is one of the 20 amino acids used by cells to build proteins, and is a molecule critical for cell survival. The microorganisms are grown in culture medium in which the histidine is present in limiting quantities (there is enough permttere histidine by only a certain number of cell divisions). So the purpose of the test is to ascertain that a compound suspected to be mutagenic to induce mutations, among which a mutation can reverse what has made it impossible for the organism to synthesize histidine. Prepare a culture for each mutagen that you want to analyze, and then used for each mutagen is also carried out a control with a neutral substance. Crops we can achieve that:
1) If you are not forming a number of colonies of the test substance is not carcinogenic. The same is observed in the control 2) If the substance is considered carcinogenic, makes the microorganisms capable of being able to re-synthesize histidine, is considered to be mutagenic. There are additional properties in the bacteria used in the Ames test: 1) have a mutation that makes additional external lamembrana readily permeable to large molecules (so that the carcinogenic potential can enter the cell)

2) have a mutation that eliminates some of the mechanisms of DNA repair

(BER and NER, respectively, ie reproduced for nucleotide excision and base excision repair)
3) is placed in a plasmid that Ellul increases the safety of the error prone DNA

(the so-called SOS shelter used by bacteria) All of these mutations sno fondamentle importance because induce the formation of many mutations in the presence of a suspected mutagen, and then changes that facilitate the accumulation and fixation of mutations.

When it comes to a carcinogen (the subject of future post), it should be noted that in reality not all are directly able to induce mutations, in fact some are carcinogenic and are called indirect pro-carcinogens, these compounds who are able to induce tumors if they undergo modifications by the cellular metabolism. Why is introduced into the culture medium extract of rat liver. In such a way as to promote the metabolism and processing of pro-carcinogens into carcinogenic substances, transformation is performed by liver enzymes.
The number of colonies formed is an indication of the strength of mutagen: many more colonies are formed much more mutagenic substance will be considered. You can make tests with increasing doses of mutagen mutagenicity analysis.