SSIble genes. 13) Which of the following best explains the Ames test for chemica

Question

SSIble genes. 13) Which of the following best explains the Ames test for chemical carcinog esting how many A) The test is useful in comparing the relative toxicity of chemica chemical kills. B) The test is used to test if the bacteria are able to use the carcinogen as a C) The test measures the rate the chemical causes mutations D) The test is measures the rate of conve carbon source. in auxotrophs that causes them to die. absence of some nutritional supplement. rsion of prototrophs to auxotrophs that are unable to grow in the E) The test measures the rate of reversion of auxotrophs back to pr ototrophs able to grow in the absence of the nutritional requirement (e g, histidine) normally supplied to allow growth of the auxotrophs 14) You conduct an Ames test on a chemical you suspect might be a carcinogen. Following incubation, you count 3 colonies on your control plate (no chemical added) and over 400 colonies on your experimental plate (chemical added). From this information, you conclude A) the chemical is not a carcinogen. B) the chemical is a likely carcinogen. C) you set up the experiment incorrectly. D) the bacteria are using the chemical as a food source. E) the results are indeterminate, and you will need to repeat the experiment. 15) Following from the previous question on the Ames test, why do you see some colonies on the control pla chemical)? A) The control plate itself is mildly carcinogenic. B) Auxotrophs are able to spontaneously mutate back to prototrophs in order to reestablish their metabolic capabilities. C) Selective pressures cause auxotrophs to alter their genetic sequence in order to restore prototroph function. D) It is unknown why some auxotrophs revert to prototrophs, but it is a widely observed phenomenon. E) Some auxotrophs revert to prototrophs given the rate of mutations that occur even with the proofreading of DNA polymerase and other DNA repair systems correcting mistakes. risnns nf hacteria and sexually reproducing

Explanation / Answer

Ames test is method that uses bacteria to test whether a given chemical or substance can causes a mutation in the test organism. As mutation are mostly linked to carcinogens, so Ames test is well defined method to check whether given chemical is carcinogen or not.

The Ames test uses several strains of the bacterium that carry mutations in genes involved in histidine synthesis such strains are known as auxotrophic mutants i.e. they require histidine for their growth, but they cannot synthesis histidine by their own.

So above method tests the capability of the substance (given chemicals) in creating mutations that result auxotrophic mutant strain back to prototrophic state, so that cells can grow in the absence of histidine in medium.

So you answer for question 13 is

E) The test measure the revisions of auxotrophs back to prototroph’s able to grow in absence of nutritional requirement (histidine) normally supplied to allow the growth of the auxotrophs.

In 2nd question mentioned as there is growth in the Control plate (count 3) where as in the test plate the colony no. increased (upto 400).

If we compare test plate with control plate, the no. of colony in the test plate is much more than the control plate which clearly says that the chemical added in the test plate is a carcinogen, which is reverting auxotrophic strain into prototroph’s strain which do not required histidine for their growth (in test plate). Whereas in control plate there’s no or less histidine was present, so the growth were restricted.

If we look for the colonies (count 3) appear in the control plate that may be due to spontaneous point mutation in the histidine encoding gene.

So you answer for question 14 is

B) The chemical is likely to be a carcinogen.

Some of the auxotroph’s can spontaneously revert back to the prototroph, it may be due to the point mutation in the histidine encoding gene and this is most widely observed phenomenon

Answer for question 15 is

Most closely

D) It is unknown why some auxotroph revert back to prototroph, but it is widely observed phenomenon

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