chapter eight: bacterial genetics

Which of the following statements regarding mutations is TRUE? a) Mutagens are nearly always carcinogens. b) Point mutations always lead to a change in a protein. c) A prototroph can grow on glucose-salts media. d) A nonsense mutation is the same thing as a silent mutation. e) Mutations happen frequently in bacteria because their DNA polymerase is error prone.

a prototroph can grow on glucose-salts media

Competent cells a) are always antibiotic resistant, are always auxotrophs, AND occur naturally. b) are able to take up naked DNA, can be created in the laboratory, AND are always antibiotic resistant. c) can be made in the laboratory, are always antibiotic resistant, AND are always auxotrophs. d) are able to take up naked DNA, occur naturally, AND are always antibiotic resistant. e) are able to take up naked DNA, occur naturally, AND can be created in the laboratory.

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

Transposons can cause mutations by a) inducing uncontrolled binary fission. b) "jumping" into a gene and disrupting its function. c) None of the answers is correct - transposons cannot cause mutations. d) replacing specific nucleotides in the original DNA. e) replacing phage nucleotides in the original DNA.

"jumping" into a gene and disrupting its function

Repair mechanisms that occur during DNA synthesis are 1. mismatch repair 2. proofreading by DNA polymerase 3. light repair 4. excision repair 5. SOS repair a) 1 and 3 b) 2 and 3 c) 1 and 2 d) 4 and 5 e) 3 and 4

1 and 2

plasmid

A DNA molecule that replicates independently of the chromosome.

mutation

A change in the nucleotide sequence of a cell's DNA that is passed on to daughter cells.

prototroph

A microorganism that does not require any organic growth factors.

auxotroph

A microorganism that requires an organic growth factor.

On which of the following DNA strands will UV light have the most effect? a) CAGTGCTAGC b) ATCCGTGCAT c) ACTTCGTTAC d) CAATCATCCT e) ACTACTACTG f) GACUUCGAGG

ACTTCGTTAC

non-homologous recombination

DNA recombination that does not require extensive nucleotide sequence similarity in the stretches that recombine.

horizontal gene transfer

DNA transfer from one bacterium to another by conjugation, DNA-mediated transformation, or transduction.

dna-mediated transformation

Mechanism of horizontal gene transfer in which "naked" DNA is taken up by the recipient cell.

transduction

Mechanism of horizontal gene transfer in which bacterial DNA is transferred inside a phage coat.

conjugation

Mechanism of horizontal gene transfer in which the donor cell physically contacts the recipient cell.

homologous recombination

Process by which a cell replaces a stretch of DNA with a segment that has a similar nucleotide sequence.

Which of the following types of repair does not require the standard DNA polymerase with proofreading capability? a) Mismatch repair b) Excision repair c) Light repair d) SOS repair e) Proofreading

SOS repair

transposon

Segment of DNA that can move from one site to another in a cell's genome.

phenotype

The observed characteristics of a cell.

genotype

The sequence of nucleotides in an organism's DNA.

vertical gene transfer

Transfer of genes from parent to offspring.

Gene transfer that requires cell-to-cell contact is a) competency. b) transduction. c) conjugation. d) functional genomics. e) transformation.

conjugation

Horizontal gene transfer can occur via a) binary fission. b) mutation. c) conjugation AND mutation. d) mitosis. e) conjugation.

conjugation

The transfer of vancomycin resistance from Enterococcus faecalis to Staphylococcus aureus is thought to have involved a) transformation AND transduction. b) transformation AND transposons. c) conjugation AND transformation. d) transduction AND transposons. e) conjugation AND transposons.

conjugation AND transposons

Bacterial cells that have been genetically modified to carry an antibiotic resistance gene can be separated from susceptible (non-resistant) microbes by using a ______ selection method using agar plates with antibiotic. a) heating b) indirect c) spread plate d) direct e) pour plate

direct

True or False: A transposon always causes a mutation.

false

True or False: All mutagens are carcinogens but not all carcinogens are mutagens.

false

A culture of E. coli is irradiated with UV light. The UV light affects the cell's DNA by a) joining the two strands of DNA together by covalent bonds. b) forming covalent bonds between cytosine and guanine bases. c) joining the two strands of DNA together by hydrogen bonds. d) forming covalent bonds between thymine bases on the same strand of DNA. e) deleting essential bases needed for protein synthesis.

forming covalent bonds between thymine bases on the same strand of dna

Is it as effective to take two antibiotics sequentially for an infection as it is to take them simultaneously, as long as the total length of time of the treatment is the same? a) Yes. Each antibiotic will kill all the cells that are sensitive to it, no matter if the drugs are taken simultaneously or sequentially. The important thing is to take the medication for as few days as possible. b) No. There's always one specific antibiotic that will be the most effective, and that is the only antibiotic that should be used to treat a particular infection. c) Yes. As long as the length of time is the same, the two treatments should be essentially the same in terms of effectively eliminating the infection. d) 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. e) No. Taken sequentially, the first antibiotic will select for the small portion of the population that will spontaneously mutate toward resistance. Then, the second antibiotic will do the exact same thing—selecting for resistance to the second drug from the few bacterial cells that remained from the first drug treatment.

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

Which is TRUE about a crown gall tumor? a) It is a unique viral infection of plants. b) It results from the transfer of a transposon to the plant. c) It results from an Agrogallerium infection of the plant. d) It results from the incorporation of bacterial plasmid DNA into the plant chromosome. e) It results from the incorporation of plant plasmid DNA into the bacterial chromosome.

it results from the incorporation of bacterial plasmid dna into the plant chromosome

Which of the following statements about the Ames test is FALSE? a) Revertants are counted. b) Liver extract is added to provide nutrients. c) Auxotrophs are used in the test. d) It relies on direct selection. e) It is used to determine whether a substance is a mutagen.

liver extract is added to provide nutrients

To increase the proportion of auxotrophic mutants in a population of bacteria, one may use a) replica plating. b) mutant reversion. c) direct selection. d) individual transfer. e) penicillin enrichment.

penicillin enrichment

Thymine dimers are removed by a) SOS repair AND photoreactivation repair. b) SOS repair, photoreactivation repair, AND excision repair. c) SOS repair AND excision repair. d) no repair mechanisms. e) Photoreactivation repair and excision repair.

photoreactivation repair and excision repair

A culture of E. coli is irradiated with UV light. The highest frequency of mutations would be obtained if after the irradiation, the cells were immediately a) placed in the dark. b) exposed to visible light. c) incubated at a suboptimal growth temperature. d) shaken vigorously. e) placed in nutrient broth.

placed in the dark

In direct selection methods used to identify possible carcinogens (example: Ames testing), what does it mean when a chemical can cause a bacterium to develop resistance to some environmental condition? a) The chemical is not carcinogenic. b) The chemical is a mutagen. c) The chemical is safe. d) The chemical is toxic. e) Not enough information.

the chemical is a mutagen

True or False: Crown gall is caused by a prokaryote plasmid that can be expressed in plant cells.

true

True or False: The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme.

true

True or False: Transposons may leave a cell by incorporating themselves into a plasmid.

true