Cacinogenicity And Mutagenicity - Ames test Flashcards
Who was Ames?
A bacterial geneticist
What is the Ames test meant to identify?
It is a test used to verify if a substance is a carcinogen or pro-cacinogenic as well as the potency of the substance in inducing cancers
Which cells did Ames perform his test on?
Salmonella cells which were histidine auxotrophs
What happens when a histidine auxotroph is placed in a medium that does not contain histidine?
They die
Which type of auxotroph did Ames choose?
He chose auxotroph which had a missense or non-sense mutation in the histidine pathway with stop codons. Therefore, by a simple base change or two base changes the original intact reading frame could be reconstituted and the cell reverts to the wild type phenotype
On a regular plate lacking histine, we expect to see a _____ rate of reversion from auxotrophy to wild type
Slow
Describe what happens when a plate of auxotrophs is treated with a mutagen/carcinogen
The rate of mutation increases dramatically therefore the rate of reversion from auxotrophy to wild type increases.
The number of colonies which grow on the plate correlates with the potency of the compound as a mutagen/carcinogen
What are pro-carcinogens?
These are compounds which are not carcinogenic on their own, but instead are converted into carcinogens within the host (usually chemically modified by the liver). The liver ‘activates’ pro-carcinogens to carcinogens
Describe the updated version of the Ames test
The test compound is mixed with an extract of rat liver, (microsomal fraction) that is rich in enzymes that can convert and modify chemicals - therefore the mutagenic properties of pro-carcinogens can also be quantified
The more bacterial colonies grow on the plate, the more _________ to wild type have occured and the more __________ the comound is as a carcinogen
Reversion, potent
How does one tell if the compound is a carcinogen or a pro-carninogen?
The Ames test must be performed twice. Once with the microsomal fraction and once without.
If the rate of reversion is the same in both: carcinogen
If the rate of reversion is higher with the microsomal fraction: procarcinogen
