Ch. 8

Insertion sequences

are the simplest type of transposon, code for a transposase enzyme, AND are characterized by an inverted repeat

Chemical mutagens that mimic the naturally occurring bases are called

base analogs

X-rays

cause single and double strand breaks in DNA molecules.

The transfer of vancomycin resistance from Enterococcus faecalis to Staphylococcus aureus is thought to have involved

conjugation AND transposons

Gene transfer that requires cell-to-cell contact is

conjugation.

Replica plating

is useful for identifying auxotrophs AND uses media on which the mutant will not grow and the parental cell typewill

In conjugation, transformation, or transduction, the recipient bacteria is most likely to accept donor DNA

from the same species of bacteria

Bacteria that have properties of both the donor and recipient cells are the result of

genetic recombination

To increase the chance of detecting carcinogens in the Ames test, the test substance is treated with

ground-up rat liver

Prokaryotic cell mutations can be observed very quickly because the prokaryotic chromosome is

haploid.

Chemical mutagens often act by altering the

hydrogen bonding properties of the nucleobase

DNA repair mechanisms occur

in both eukaryotes and prokaryotes

Planar molecules used as chemical mutagens are called

intercalating agents

Segments of DNA capable of moving from one area in the DNA to another are called

inverted repeats

Among the easiest of the mutations to isolate are those which

involve haploid chromosomes AND involve antibiotic resistance.

Indirect selection

is necessary to isolate auxotrophic mutants

A clever technique that streamlines the identification of auxotrophic mutants is

replica plating.

The designation his- refers to

the genotype of a bacterium that lacks a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine

The diploid character of eukaryotic cells may mask the appearance of a mutation since

the matching chromosome may carry the dominant gene.

Direct selection involves inoculating cells onto growth media on which

the mutant but not the parental cell type will grow

The F plasmid carries the information for

the sex pilus

Irradiation of cells with ultraviolet light may cause

thymine dimers

The mechanism by which genes are transferred into bacteria via viruses is called

transduction.

Which is not true about a crown gall tumor?

A. It is a bacterial infection of plants. B. It requires a plasmid. C. It produces a large amount of opines that neither the plant nor bacteria synthesizes. D. It is due to the incorporation of bacterial plasmid DNA into the plant chromosome. E. All of the choices are true

Transposons

A. are informally known as jumping genes. B. may cause insertion mutations. C. may cause knockout mutations. D. were first recognized in plants. E. All of the choices are correct.

On which of the following DNA strands would UV radiation have the most effect?

AATTAGTT

Which change in a gene's DNA sequence would have the least effect on the eventual amino acid sequence produced from it?

Addition/deletion of three consecutive nucleotides

A quick microbiological test for potential carcinogens was developed by

Ames.

The material responsible for transformation was shown to be DNA by

Avery, MacLeod, and McCarty

DNA transfer by conjugation is more efficient in a liquid medium setting, subjected to very mild agitation (stirring), rather than on an agar plate format. Why?

Direct cell-to-cell contact is required for this process, and this is more likely to be achieved in the fluid liquid format than on an agar plate (especially for relatively non-motile types of bacteria).

Strong chemical mutagens may be used to treat cancer cells. Is this a good or bad idea?

Good and bad-they're very good at killing cancer cells, but depending on mode of administration, they could also be dangerous to non-cancerous cells.

Is it as effective to take two antibiotics sequentially for an infection as it is to take them simultaneously, so long as the total length of time of the treatment is the same?

It depends. Provided that the majority of the infectious agent is killed off by the first drug, the likelihood that the few that are left would not also be killed by the second drug is low. However, simultaneous treatment should be more effective at eliminating all the microbes in the shortest time possible, and with the least probability of selection for multiple drug resistance mutations

To maximize the number of thymine dimer mutations following UV exposure, should you keep human cells in tissue culture in the dark, in the light, or does it matter at all?

It doesn't matter-human cells don't possess the enzymes needed for photorepair of thymine dimers.

Which is not true about mismatch repair?

It removes both strands in the mismatch area

Two bacterial genes are transduced simultaneously. What does this suggest about their proximity to each other within the original host genome?

It's highly likely that the two genes are located next to each other in the original host cell chromosome. Since transduction relies on either mispackaging of bits of host cell DNA into non-functional virus units, or improper excision of lysogenic phage DNA from a host cell chromosome (carrying parts of the host cell DNA with it), the genes must lie close to each other to be transduced into a new cell simultaneously.

Every 24 hours, every genome in every cell of the human body is damaged 10,000 times or more. Given the possible DNA repair mechanisms, which order listed below would be most effective at repairing these as quickly as possible in order to prevent mutations from being carried forward in DNA replication?

Proofreading by DNA polymerase, glycosylase enzyme activities, excision repair, SOS repair

Some bacteria have a higher incidence rate of thymine dimer mutations following exposure to UV light than others. What might be going on here to lead to this outcome?

They may simply have a higher proportion of T nucleotides next to each other in their DNA sequences than other bacteria, leading to more possible dimers being formed AND they may have a weaker expression of photoreactivation enzymes, leading to more thymine dimers being formed and retained.

The formation of a covalent bond between two adjacent thymines is caused by

UV radiation

The study of the crown gall tumor found

a bacterial plasmid promoter that was similar to plant promoters

The Ames test is useful as a rapid screening test to identify those compounds that

are mutagens.

Intercalating agents

act during DNA synthesis AND often result in frameshift mutations

The largest group of chemical mutagens consists of

alkylating agents.

In conjugation the donor cell is recognized by the presence of

an F plasmid.

Competent cells

are able to take up naked DNA, occur naturally, AND can be created in the laboratory

The source of variation among microorganisms that were once identical is

mutation.

To increase the proportion of auxotrophic mutants in a population of bacteria, one may use

penicillin enrichment

The characteristics displayed by an organism in any given environment is its

phenotype.

The properties of a cell that are determined by its DNA composition are its

phenotype.

Thymine dimers are dealt with by

photoreactivation repair AND excision repair

Antibiotics

provide an environment in which preexisting mutants survive