Chapter 14

How may a tautomeric shift lead to a mutation? -It allows hydrogen bonding of normally noncomplementry bases. -It allows hydrogen bonding between the nitrogenous bases of the same strand of DNA -It allows deletion of one or more bases in the template strand of DNA -It allows the insertion of one or more bases in the template strand of DNA

-It allows hydrogen bonding of normally noncomplementary bases

Why are liver extracts used in the Ames test? -Liver enzymes may activate some innocuous compounds, making them mutagenic. -A live extract is necessary for the bacteria to produce histidine revertants. -The bacteria require the nutrients present in the liver extract for growth -Liver enzymes activate the bacterial enzymes

-Liver enzymes may activate some innocuous compounds, making them mutagenic

What is tautomeric shift? -tautomeric shift is an intramoleculr proton shift that changes the bonding structure of the molecule -tautomeric shift is an intramolecular electron shift that changes the bonding structure of the molecule -tautomeric shift is an intermolecular proton shift that changes the bonding structure of the molecule

-Tautomeric shift is an intramolecular proton shift that changes the bonding structure of the molecule

In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that ______________________. -there is some low-level contamination in most experiments -the growth medium contains factors that are mildly mutagenic -some of the reversion mutations are not caused by the mutagen being tested -liver extract increases the potency of some mutagens

-some of the reversion mutations are not caused by the mutagen being tested

Mutations that arise in nature, from no particular artificial agent, are called _____________________. -oblique mutations -induced mutations -spontaneous mutations -cosmic mutations -chromosomal aberrations

-spontaneous mutations

The purpose of the Ames Test is to ____________________. -determine whether histidine has mutagenic effects in S typhimurium -determine whether Salmonella typhimurium his- mutants can revert to his+ -test the mutagenic effects of chemicals -study how the liver affects potential mutagens

-test the mutagenic effects of chemicals

T/F A missense mutation causes premature chain (protein) termination.

F

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

F

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

T

T/F When treating an organism with a mutagen, although it is possible that homozygous mutations will occur, it is more likely that most new mutations will occur, it is more likely that most new mutations will be heterozygous or hemizygous.

T

Why would a mutation in a somatic cell of a multicellular organism escape detection? -Most somatic mutations are dominant and do not cause a phenotypic change in the cell. As a result, it is highly unlikely that the organism will be sufficiently altered to respond to a screen. -A somatic mutation is a type of mutation that can be easily repaired. Therefore, the mutation is often corrected before the genetic screen takes place. -Most somatic mutations are recessive and do not cause a phenotypic change in the cell. As a result, it is highly unlikely that the organism will be sufficiently altered to respond to a screen. -When conducting genetic screens, it is assumed that all the cells are genetically identical. Since a somatic mutation first appears in a single cell, it is highly unlikely that the organism will be sufficiently altered to respond to a screen because none of the other cells will have the mutation.

-When conducting genetic screens, it is assumed that all the cells are genetically identical. Since somatic mutation first appears in a single cell, it is highly unlikely that the organism will be sufficiently altered to respond to a screen because none of the other cells will have the mutation

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene? -a base substitution at the beginning of the gene -a base substitution at the end of the gene -a frameshift deletion at the beginning of the gene -a frameshift deletion at the end of the gene

-a frameshift deletion at the beginning of the gene

Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted? -because they are likely to change more than one amino acid -because they are likely to damage ribosomes -because their effect extends to all chromosomes -because their effect is likely to be detrimental for transcription

-because they are likely to change more than one amino acid

The Ames test is used to determine whether or not a compound causes ___________________. -gene mutations -radiation mutagenesis -DNA repair -chromosome mutations

-gene mutations

Which bacteria grow on the agar plate if the Ames test is positive? -his- prototrophs -his- auxotrophs -his+ prototrophs -his+ auxotrophs

-his+ prototrophs