The Ames Test Is Used to Test the Mutagenicity of a Compound

question 46

Multiple Choice

The Ames test is used to test the mutagenicity of a compound suspected to be a carcinogen. In a simple form of the test, the carcinogen is first mixed with a rat liver extract. A disc of filter paper is soaked with this mixture and placed on a culture of a strain of Salmonella typhimurium that is defective in a gene involved in the synthesis of histidine, an amino acid that is essential for cell growth and proliferation. The strain is thus normally unable to grow into visible colonies when the histidine in the culture medium is depleted. In the presence of a mutagen, however, mutations (often "reverse mutations" in the same gene) can enable the bacteria to produce histidine on their own, and therefore grow into colonies. The results of the Ames test for three compounds A, B, and C-each used at the same concentration-are shown in the schematic diagram below. Colonies are indicated with black dots, and the disc is indicated with a white circle at the center of each plate. Which compound (A to C) appears to be a stronger mutagen in this assay? Write down A, B, or C as your answer.

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Definitions:

Carotid Arteries

Major arteries located on each side of the neck that supply blood to the brain, neck, and face.

Bruits

Sounds heard through a stethoscope over blood vessels, indicating turbulence due to narrowing or blockage.

Amplitude

The magnitude or extent of change in a variable or oscillation, often used in physics to denote the maximum displacement from equilibrium.

Dyspnea

A subjective experience of breathing discomfort that varies in intensity, commonly described as shortness of breath.