Microbiology Ch. 8

Please select the INCORRECT statement regarding mutation. - A reversion is a mutation that corrects a defect caused by an earlier mutation. - A base substitution is a mutation in which the wrong nucleotide has been incorporated. - A missense mutation is also called a synonymous mutation, meaning no change in the amino acid encoded. - Insertional inactivation is the disruption of a gene's function due to a DNA segment inserted into the gene. - Spontaneous mutations are those that occur during the normal processes of a cell

A missense mutation is also called a synonymous mutation, meaning no change in the amino acid encoded.

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 - SOS repair, excision repair, glycosylase enzyme activities, proofreading by DNA polymerase - SOS repair, proofreading by DNA polymerase, glycosylase enzyme activities, excision repair - Glycosylase enzyme activities, SOS repair, proofreading by DNA polymerase, excision repair - Proofreading by DNA polymerase, SOS repair, glycosylase enzyme activities, excision repair

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

If you were carrying out a penicillin enrichment culture and you forgot to add penicillinase before plating the sample onto nutrient agar, what would happen? - You would get the same results whether you add this enzyme of not because penicillin naturally rapidly degrades in agar. The prototrophs would be able to grow on the agar plates but the auxotrophs would not. The auxotrophs would be able to grow on the agar plates but the prototrophs would not. - Prototrophs and auxotrophs would both be killed by the penicillin; only PenR mutants would grow and you would not enrich for auxotrophs. - Prototroph and auxotroph colonies would change color from cream to red in the presence of the penicillin

Prototrophs and auxotrophs would both be killed by the penicillin; only PenR mutants would grow and you would not enrich for auxotrophs.

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

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

Which of the following about transposons is not true? - They are informally known as jumping genes. - They may cause insertion mutations. - They may cause knockout mutations. - They were first recognized in fungi. - All of the statements are true.

They were first recognized in fungi.

A mutation in E. coli results in the loss of both restriction endonucleases and modification enzymes. Would you expect any difference in the frequency of gene transfer via transduction FROM Salmonella INTO this E. coli strain? - No—since the Salmonella strain is normal, the rate of production of transducing virus particles would still be the same, resulting in the same frequency of gene transfer. - Yes—the loss of the restriction endonucleases would leave the recipient E. coli unable to break down "invading"' viral DNA from the transducing phage. This would lead to higher rates of successful transduction. - Yes—the loss of the modification enzymes would leave the recipient E. coli unable to tag its own DNA as "self," leaving the viral DNA untagged and recognizable as "foreign," and targeted for destruction. This would lead to higher rates of successful transduction. - No—transduction efficiency isn't affected by either restriction endonucleases or modification enzymes, so there'd be no effect on the overall rate. - Yes—the loss of the restriction endonucleases would leave the recipient E. coli unable to break down "invading" viral DNA from the transducing phage, AND the loss of the modification enzymes would leave the recipient E. coli unable to tag its own DNA as "self," leaving the viral DNA untagged and recognizable as "foreign," and targeted for destruction. Together, these would lead to higher rates of successful transduction

Yes—the loss of the restriction endonucleases would leave the recipient E. coli unable to break down "invading" viral DNA from the transducing phage, AND the loss of the modification enzymes would leave the recipient E. coli unable to tag its own DNA as "self," leaving the viral DNA untagged and recognizable as "foreign," and targeted for destruction. Together, these would lead to higher rates of successful transduction.

Intercalating agents - act during RNA synthesis AND often result in frameshift mutations. - act during RNA synthesis AND change the hydrogen bonding properties of nucleotides. - act during DNA synthesis AND often result in frameshift mutations. - change the hydrogen bonding properties of nucleotides AND always result in nonsense mutations. - act during DNA synthesis AND always result in nonsense mutations

act during DNA synthesis AND often result in frameshift mutations.

The largest group of chemical mutagens consists of - radiation. - alkylating agents. - nitrous acid. - base analogs. - intercalating agents.

alkylating agents.

In conjugation the donor cell is recognized by the presence of - an F plasmid. - a Y chromosome. - diploid chromosomes. - an SOS response. - an F plasmid AND diploid chromosomes.

an F plasmid.

Competent cells - are able to take up naked DNA, can be created in the laboratory, AND are always antibiotic resistant. - are able to take up naked DNA, occur naturally, AND can be created in the laboratory. - are always antibiotic resistant, are always auxotrophs, AND occur naturally. - can be made in the laboratory, are always antibiotic resistant, AND are always auxotrophs. - are able to take up naked DNA, occur naturally, AND are always antibiotic resistant

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

The Ames test is useful as a rapid screening test to identify those compounds that - will respond to chemical agents. - are mutagens. - respond to the deletion of DNAses. - will protect an organism from cancer. - will respond to chemical agents AND will protect an organism from cancer

are mutagens

Insertion sequences - are the simplest type of transposon, code for a transposase enzyme AND can produce pili. - code for a transposase enzyme AND are characterized by an inverted repeat. - are characterized by an inverted repeat AND can produce pili. - can produce pili AND are the simplest type of transposon. - are the simplest type of transposon, code for a transposase enzyme, AND are characterized by an inverted repeat.

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

X-rays - have no effect on DNA. - cause thymine trimers. - cause breaks in DNA molecules. - make the DNA radioactive. - destroy lipopolysaccharide

cause breaks in DNA molecules.

Not all bacteria can take up DNA from the environment. Those that can are referred to as - mutants. - F−. - F+. - competent. - transducers

competent.

In conjugation, transformation, or transduction, the recipient bacteria is most likely to accept donor DNA - from any source. - from any species of bacteria. - from the same species of bacteria. - only through plasmids. - from any source AND only through plasmids

from the same species of bacteria.

To increase the chance of detecting carcinogens in the Ames test, the test substance is treated with - penicillin. - heat. - ground-up rat liver. - reverse transcriptase. - penicillin AND heat

ground-up rat liver.

DNA repair mechanisms occur - only in prokaryotes. - only in eukaryotes. - in both eukaryotes and prokaryotes. - in neither eukaryotes nor prokaryotes. - None of the answer choices is correct

in both eukaryotes and prokaryotes.

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

penicillin enrichment.

The characteristics displayed by an organism in any given environment is its -archaetype. - phenotype. - genotype. - mutatotype. - phenogene

phenotype.

Thymine dimers are removed by - no repair mechanisms. - SOS repair AND photoreactivation repair. - SOS repair AND excision repair. - photoreactivation repair AND excision repair. - SOS repair, photoreactivation repair AND excision repair

photoreactivation repair AND excision repair.

Antibiotics - cause mutations to occur. - may act as alkylating mutagens. - provide an environment in which preexisting mutants survive. - increase the rate of spontaneous mutation. - destroy all mutant bacteria

provide an environment in which preexisting mutants survive.

A clever technique that streamlines the identification of auxotrophic mutants is - gas chromatography. - replica plating. - direct selection. - reversion. - intercalation

replica plating.

The designation his- refers to - the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine. - the genotype of bacteria that have a functional gene for histidine synthesis AND bacteria that require addition of histidine to the growth medium. - the genotype of bacteria that have a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine. - the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that have a hers gene. - the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that do not require addition of histidine to the growth medium

the genotype of bacteria that lack 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 correct version of the gene. - the matching chromosome may repair the mutated gene. - the mutation is usually reversible. - the mutation may create inverted repeats. - All answer choices are correct.

the matching chromosome may carry the correct version of the gene.

Direct selection involves inoculating cells onto growth media on/in which - the mutant but not the parental cell type will grow. - the mutation will be reversed. - the nutrients necessary for mutation to occur are present. - the mutagen is present. - histidine has been added

the mutant but not the parental cell type will grow.

The F plasmid carries the information for - the sex pilus. - recipient cell DNA replication. - antibiotic resistance. - the Y chromosome. - bacterial flagella

the sex pilus.

Irradiation of cells with ultraviolet light may cause - four nucleotides to covalently bind together. - thymine dimers. - adenine complementary base - pairing with cytosine. - the addition of uracil. - cytosine trimers

thymine dimers.

The mechanism by which genes are transferred into bacteria via viruses is called - ellipsis. - transduction. - replica plating. - transformation. - conjugation

transduction.

Segments of DNA capable of moving from one area in the DNA to another are called - base analogs. - intercalating agents. - transposons. - inverted repeats. - mutagens

transposons.

In order for insertional inactivation to occur, the transposon must be placed - upstream from the gene in question. - downstream from the gene in question. - within the gene in question. - randomly in the genome. - in an intron

within the gene in question.

Strong chemical mutagens may be used to treat cancer cells. Is this a good or bad idea? - Good—kill those cancer cells as quickly as possible to cure the patient! - Bad—these mutagens will also affect the non-cancerous cells, possibly leading to new cancerous states! - Good and bad—they're very good at killing cancer cells, but they could also be dangerous to non-cancerous cells. Correct - Bad—the cancer cells are already mutated. We don't want to mutate them more and make them more cancerous! - Bad—the medications are toxic and will cause healthy normal microbiots to become cancerous

Good and bad—they're very good at killing cancer cells, but they could also be dangerous to non-cancerous cells.

Which of the following statements about spontaneous mutation is TRUE? - A single mutation is common but a double mutation is very rare. - If the mutation rate to antibiotic A is 10-9 per cell division, and to antibiotic B is 10-6 per cell division, the probability of the cell being resistant to both medications is 10-15. - If the mutation rate to antibiotic A is 10-9 per cell division, and to antibiotic B is 10-6 per cell division, the probability of the cell being resistant to both medications is 10-54. - A frameshift mutation in which three nucleotides are added is less likely to impact a cell that a frameshift mutation in which two nucleotides are deleted. - A transposon may insertionally inactivate a gene when it jumps from one place in a genome to another.

If the mutation rate to antibiotic A is 10-9 per cell division, and to antibiotic B is 10-6 per cell division, the probability of the cell being resistant to both medications is 10-15.

The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme. T/F

True

Transposons may leave a cell by incorporating themselves into a plasmid. T/F

True

A quick microbiological test for potential carcinogens was developed by - Fleming. - Lederberg. - Ames. - Crick. - McClintock

Ames.

On which of the following DNA strands would UV radiation have the most effect? - AATTAGTTC - AACCGGG - TATATACG - AUAUCGAU - TATATACG AND AATTAGTTC

AATTAGTTC

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 plate format than in the fluid format (especially for relatively non-motile types of bacteria). - Direct cell-to-cell contact isn't required for this process, so the ability to secrete the DNA into the surrounding fluid medium makes the process more efficient than the dry surface of an agar plate. - 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). - Trick question—it can take place with the same degree of efficiency on either format. It doesn't matter! - Agitation is only needed if the bacteria are known to be non-motile and can't move around on a solid medium. Otherwise, it doesn't really matter what type of medium is used as long as it contains chemicals to make cells competent

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).

Organisms termed his- are considered prototrophic for histidine. T/F

False

The Ames test determines antibiotic sensitivity of a bacterium. T/F

False

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? - 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. - 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. - 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. - 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

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? - the dark—light will activate the photorepair systems that can break thymine dimers induced by UV light. - The light—it's important to keep on producing the thymine dimers by keeping the plate exposed to light as much as possible. - Alternating light and dark every hour to increase the chances that thymine dimers will form, but prevent photorepair systems from correcting them as they are formed. - It doesn't matter—human cells don't have the enzymes needed for photorepair of thymine dimers. - Alternating light and dark every 24 hours to increase the chances that thymine dimers will form

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

Which is not true about mismatch repair? - It uses an endonuclease. - It requires DNA polymerase and DNA ligase. - It uses methylation of the DNA to differentiate between strands. - It removes both strands in the mismatch area. - It fixes errors missed by the proofreading of DNA polymeras

It removes both strands in the mismatch area.

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

Two bacterial genes are transduced simultaneously. What does this suggest about their proximity to each other within the original host genome? - Nothing. It's highly likely that two separate virus particles were carrying each gene, and that they coinfected the new target cell at the same time. This could mean the two original genes might not even be from the same original host cell! - It's highly likely that the two genes are located next to each other in the host cell chromosome. Since transduction results from a packaging error or an excision error that occurs during the infection cycle of the bacteriophage, the genes must lie close to each other to be transduced into a new cell simultaneously. - They must be within five gene lengths of each other, but not necessarily immediately adjacent. If they were immediately adjacent, the transposons that facilitate the transfer of genetic information between the two cells wouldn't be able to "jump" into them. - It doesn't mean anything. Transduction relies on the ability of a cell to take up foreign DNA. It's possible here that the cell has simply taken up two separate bits of DNA at the same time from the surrounding environment. - It's highly likely that one gene was on the chromosome but the other was actually on a plasmid; if those two elements are in one cell, genes can be transferred simultaneously.

It's highly likely that the two genes are located next to each other in the host cell chromosome. Since transduction results from a packaging error or an excision error that occurs during the infection cycle of the bacteriophage, the genes must lie close to each other to be transduced into a new cell simultaneously.

You mix two bacterial stains in a tube of glucose-salts agar. One strain is His−, Val−, while the other strain is Trp−, Leu−. You previously showed that neither strain grows on glucose-salts agar. After incubating the tube, you plate a sample onto a new glucose-salts agar plate. Several colonies grow. What do you know is TRUE about these colonies? -The bacteria in the colonies are His−, Val−, Trp+, Leu+. - The bacteria in the colonies are His−, Val+, Trp+, Leu+. - The bacteria in the colonies are His−, Val−, Trp−, Leu−. - The bacteria in the colonies are His+, Val+, Trp+, Leu+. - The bacteria in the colonies are His+, Val+, Trp+, Leu+, PenR

The bacteria in the colonies are His+, Val+, Trp+, Leu+.

A bacterial strain is resistant to infection by a bacteriophage. Which statement is FALSE? - The bacteria make restriction enzymes that degrade the virus genome. - The bacterial host DNA is protected from restriction enzyme degradation by phosphorylation. - The bacterial host DNA is protected from restriction enzyme degradation by methylation. - If the phage DNA was methylated, it would be protected from restriction enzyme degradation. - The statements are ALL false

The bacterial host DNA is protected from restriction enzyme degradation by phosphorylation.

Crown gall is caused by a prokaryote plasmid that can be expressed in plant cells. T/F

True

DNA polymerase is able to proofread the DNA sequence. T/F

True

Each gene mutates at a characteristic frequency. T/F

True

F plasmids and oftentimes R plasmids are both able to code for production of a pilus. T/F

True

Mutations are likely to persist after SOS repair, but not after light-induced or excision repair. T/F

True

Plasmids often carry the information for antibiotic resistance. T/F

True

The formation of a covalent bond between two adjacent thymines is caused by - X-rays. - alkylating agents. - UV radiation. - microwave radiation. - heat.

UV radiation.

Chemical mutagens that mimic the naturally occurring bases are called - nitrogen mustards. - alkylating agents. - base analogs. - nitrous oxide. - nucleobase copiers

base analogs.

The study of the crown gall tumor found - a bacterial plasmid promoter that was similar to plant promoters. - an R plasmid in plant cells. - incorporation of the bacterial chromosome into the plant. - incorporation of the plant chromosome into the bacteria. - a bacterial plasmid promoter that was similar to plant terminators

a bacterial plasmid promoter that was similar to plant promoters.

Gene transfer that requires cell-to-cell contact is - transformation. - competency. - conjugation. - functional genomics. - transduction

conjugation.

The clustered, regularly interspaced short palindromic repeats (CRISPR) system in bacterial cells has been called the "immune" system of bacteria. CRISPR protect bacteria from a repeat infection from the same phage because bacterial cells - recognize proteins on the surface of the phage and secrete enzymes that digest the phage. - recognize proteins on the surface of the phage and secrete proteins that block the binding of the phage. - integrate fragments from the phage DNA in their own chromosomes and target for destruction any DNA that contains the same fragments in the future. - modify the attachment sites for the phages so that new infections cannot take place. - integrate fragments from the phage RNA in their own chromosomes and target for destruction any RNA that contains the same fragments in the future

integrate fragments from the phage DNA in their own chromosomes and target for destruction any DNA that contains the same fragments in the future.

Among the easiest of the mutations to isolate are those which - involve polyploid chromosomes AND allow populations to be measured. - involve antibiotic resistance AND allow populations to be measured. - allow populations to be measured AND use an indirect method for measurement. - involve haploid chromosomes AND involve antibiotic resistance. - use an indirect method for measurement AND involve antibiotic resistance

involve haploid chromosomes AND involve antibiotic resistance.

Replica plating - is useful for direct selection of antibiotic resistance AND is useful for identifying auxotrophs. - uses media on which the mutant will grow but the parental cell type will not AND is useful for identifying prototrophs. - is useful for identifying auxotrophs AND uses media on which the mutant will not grow but the parental cell type will. - is useful for identifying auxotrophs AND uses media on which the mutant will grow but the parental cell type will not. - is useful for direct selection of antibiotic resistance AND is useful for identifying prototrophs

is useful for identifying auxotrophs AND uses media on which the mutant will not grow but the parental cell type will.

DNA is protected from restriction enzymes by being - sequestered in a lysosome. - turned into RNA. - methylated. - made into double-stranded RNA. - phosphorylated

methylated.

The source of variation among microorganisms that were once identical is - antibiotic resistance. - virulence factors. - mutation. - sigma factors. - mutant

mutation.