Lecture 4: The Ames Test and the Mouse Test

Question 1

Which test is used to identify mutagens?

Answer 1

Ames Test

Question 2

Which test is used to identify carcinogens?

Answer 2

Mouse test

Question 3

Why are human cells not used in the Ames test?

Answer 3

1) Human cells don’t grow well in a dish.

2) Human cells need too many hits to cause cancer.

Question 4

What is the negative control for the Ames Test?

Answer 4

Water or salt water

Question 5

True or false: All mutagens are carcinogens.

Answer 5

True

Question 6

How can the Ames test be modified to simulate how mammalian liver enzymes would alter a compound?

Answer 6

A liver extract is added to the plate.

Question 7

What type of DNA is used in the Ames Test?

Answer 7

Bacterial DNA (salmonella tymphimurium)

Question 8

What mutation is induced in the bacteria used in the Ames Test?

Answer 8

Their genotype is his-; this means that the gene encoding an enzyme used to synthesize histidine (a necessary amino acid) will not function correctly.

Question 9

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?

Answer 9

They will die.

Question 10

How does the Ames Test identify mutagens?

Answer 10

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.

Question 11

What is the positive control for the Ames Test?

Answer 11

Sodium Azide

Question 12

What are the downsides of the Ames Test for detecting mutagens that will mutate human DNA?

Answer 12

1) It is conducted in vitro, not in vivo.

2) It is conducted in prokaryotes instead of eukaryotes.

Question 13

What are the downsides of using prokaryotes instead of eukaryotes to identify chemicals that are mutagenic in humans?

Answer 13

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.

Question 14

Why does the Ames Test identify mutagens, but not carcinogens?

Answer 14

1) Because it is carried out in vitro, not in vivo.

2) Because it uses prokaryotic cells, not eukaryotic cells.

Question 15

What percentage of mutagens identified by the Ames Test are carcinogens?

Answer 15

75%

Question 16

Which two categories within the EPA rating system label a substance as a carcinogen or a likely carcinogen?

Answer 16

Group A (carcinogenic to humans) and Group B (likely to be carcinogenic to humans)

Question 17

What would the EPA label a substance that causes cancer in 100% of the mice it is tested on in a mouse test?

Answer 17

Group A (carcinogenic to humans-100% penetrance)

Question 18

What would the EPA label a substance that causes cancer in only one mouse in a mouse test?

Answer 18

Group B (likely carcinogenic to humans)

Question 19

What would the EPA label a substance that causes cancer in 99% of mice it is tested on in a mouse test?

Answer 19

Group B (likely carcinogenic to humans)

Question 20

Where does the EPA’s categories for the carcinogenicity of substances come from?

Answer 20

1) Ames test

2) Mouse test

Question 21

What are the steps for determining if a substance is carcinogenic?

Answer 21

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)