Gen Chap 15

Which of the following events could result in a frameshift mutation?

Base Deletion A base deletion would shorten the DNA sequence and change the reading frame of the mRNA.

T or F All compounds that have been found to be mutagenic in the Ames test are also carcinogenic.

False The Ames test is used as a preliminary screening tool. Not all compounds that give a positive Ames test are carcinogenic.

Which nucleotide will base‑pair with the enol form of 5‑bromouracil?

Guanine The enol form of 5‑bromouracil forms a base pair with guanine.

Why are liver extracts used in the Ames test?

Liver enzymes may activate some innocuous compounds, making them mutagenic. Some compounds are innocuous until they are activated metabolically by liver enzymes.

What is a spontaneous mutation?

Mutations that occur as a result of natural biological and/or chemical processes are considered spontaneous.

Why are spontaneous mutations rare?

They are relatively rare in comparison to induced mutations that are more directed to the physical or chemical properties of DNA.

T or F Many chemicals are more mutagenic after being processed in the liver.

True Many potential mutagens are poorly mutagenic until passing through the liver.

T or F Tautomers of nucleotide bases are isomers that differ from each other in the location of one hydrogen atom in the molecule.

True Nucleotide tautomers differ only in the bonding location of one hydrogen atom.

Why are X rays more potent mutagens than UV radiation?

X rays are of higher energy and shorter wavelength than UV light. They have greater penetrating ability and can create more disruption of DNA.

Which bacteria grow on the agar plate if the Ames test is positive?

his+ prototrophs The bacteria used in the Ames test to evaluate mutagenicity are his− auxotrophs. If the Ames test is positive, these bacteria have reverted back to wild type and are his+ prototrophs

In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that _______.

some of the reversion mutations are not caused by the mutagen being tested His+ revertants on the control plate are the result of spontaneous mutation.

The purpose of the Ames Test is to _______.

test the mutagenic effects of chemicals The Ames test detects whether a given chemical can cause a reversion mutation in his- bacteria.