Lecture 4: The Ames Test and the Mouse Test Flashcards
Which test is used to identify mutagens?
Ames Test
Which test is used to identify carcinogens?
Mouse test
Why are human cells not used in the Ames test?
1) Human cells don’t grow well in a dish.
2) Human cells need too many hits to cause cancer.
What is the negative control for the Ames Test?
Water or salt water
True or false: All mutagens are carcinogens.
True
How can the Ames test be modified to simulate how mammalian liver enzymes would alter a compound?
A liver extract is added to the plate.
What type of DNA is used in the Ames Test?
Bacterial DNA (salmonella tymphimurium)
What mutation is induced in the bacteria used in the Ames Test?
Their genotype is his-; this means that the gene encoding an enzyme used to synthesize histidine (a necessary amino acid) will not function correctly.
What will happen to the His- bacteria in the Ames Test if no histidine or mutagen is added to the plate in which they are growing?
They will die.
How does the Ames Test identify mutagens?
If a chemical added to the plate is mutagenic, the bacteria will convert from his- to his +, enabling them to synthesize histidine and thereby grow and survive in media lacking histidine.
What is the positive control for the Ames Test?
Sodium Azide
What are the downsides of the Ames Test for detecting mutagens that will mutate human DNA?
1) It is conducted in vitro, not in vivo.
2) It is conducted in prokaryotes instead of eukaryotes.
What are the downsides of using prokaryotes instead of eukaryotes to identify chemicals that are mutagenic in humans?
1) Eukaryotes repair their DNA differently than prokaryotes.
2) There is a cell wall in prokaryotes, so different cell absorption.
3) Eukaryotic and prokaryotic cells have different systems for getting things out of the cell.
Why does the Ames Test identify mutagens, but not carcinogens?
1) Because it is carried out in vitro, not in vivo.
2) Because it uses prokaryotic cells, not eukaryotic cells.
What percentage of mutagens identified by the Ames Test are carcinogens?
75%
Which two categories within the EPA rating system label a substance as a carcinogen or a likely carcinogen?
Group A (carcinogenic to humans) and Group B (likely to be carcinogenic to humans)
What would the EPA label a substance that causes cancer in 100% of the mice it is tested on in a mouse test?
Group A (carcinogenic to humans-100% penetrance)
What would the EPA label a substance that causes cancer in only one mouse in a mouse test?
Group B (likely carcinogenic to humans)
What would the EPA label a substance that causes cancer in 99% of mice it is tested on in a mouse test?
Group B (likely carcinogenic to humans)
Where does the EPA’s categories for the carcinogenicity of substances come from?
1) Ames test
2) Mouse test
What are the steps for determining if a substance is carcinogenic?
1) Ames test; if positive, the substance is a mutagen and will be tested with the mouse test for carcinogenicity.
2) Test it on mice (mammal in vivo–injection, inhalation, skin)
