Chapter 8 Quiz

The material responsible for transformation was shown to be DNA by Lederberg. Stanley. Beadle and Tatum. Avery, MacLeod, and McCarty. Watson and Crick.

Avery, MacLeod, and McCarty.

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

UV radiation

Which change in a gene's DNA sequence would have the least effect on the eventual amino acid sequence produced from it? Addition of two consecutive nucleotides Deletion of two consecutive nucleotides Addition of one nucleotide Substitution of one nucleotide AND addition of one nucleotide Addition or deletion of three consecutive nucleotides

Addition or deletion of three consecutive nucleotides

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

Ames

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? 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 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!

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).

Double-stranded DNA enters the recipient cell during transformation. True False

False

Organisms termed his- are considered prototrophic for histidine. True False

False

The Ames test determines antibiotic sensitivity of a bacterium. True False

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. 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. 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.

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 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. The dark—light will activate the photorepair systems that can break thymine dimers induced by UV light. 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.

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

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. On further reading, you learn that strains of H. influenzae vary genotypically. Many of them have silent mutations. Select the TRUE statement regarding this type of mutation. It is a frameshift mutation—base pairs are added or deleted, causing the change of one or more amino acids in the protein but does not affect the function of that protein. It is a point mutation—a single base pair is altered, causing the change of one amino acid in the protein that does not affect the function of that protein. It is a point mutation—a single base pair is altered, causing the change of one amino acid in the protein that changes the function of that protein. It is a point mutation—several base pairs are altered, causing the change of many amino acids in the protein that completely changes the function of that protein. It is a point mutation—a single base pair is altered, causing the change of one amino acid in the protein that stops the correct formation of a protein.

It is a point mutation—a single base pair is altered, causing the change of one amino acid in the protein that does not affect the function of that protein.

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

Mutation

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

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? The prototrophs would be able to grow on the agar plates but the auxotrophs would not. Prototrophs and auxotrophs would both be killed by the penicillin; only PenR mutants would grow and you would not enrich for auxotrophs. The auxotrophs would be able to grow on the agar plates but the prototrophs would not. Prototroph and auxotroph colonies would change color from cream to red in the presence of the penicillin. You would get the same results whether you add this enzyme of not because penicillin naturally rapidly degrades in agar.

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

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis. The lab results indicate that the pus from your patient's "bite" contains clusters of spherical cells that stained purple in the Gram stain. You tell your patient that his wound contains bacteria from the genus ______ and is classified as a ________ organism.

Staphylococcus; Gram-positive

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis. Your patient asks why the penicillin he has been taking hasn't helped his infection. Which of the following is a possible explanation for your patient? Bacteria are never killed by a single type of antibiotic; combinations of drugs are needed. Penicillin has been overused by people and it no longer works against any bacteria; it can be used against viruses. The patient's body is neutralizing the antibiotic; he needs to take a probiotic to help the penicillin work. The patient has become resistant to penicillin and he needs to take a different medication. The bacteria causing the infection are resistant to penicillin; a different antibiotic is needed.

The bacteria causing the infection are resistant to penicillin; a different antibiotic is needed.

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 methylation. If the phage DNA was methylated, it would be protected from restriction enzyme degradation. The bacterial host DNA is protected from restriction enzyme degradation by phosphorylation. The statements are ALL false.

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

You make two agar plates: one is a nutrient agar plate (plate A) that contains histidine and penicillin. The other is a glucose salts agar (plate B) that also contains penicillin. You inoculate a sample onto both plates using replica plating technique, incubate the plates, and compare the growth after 48 hours. There are 12 colonies on the nutrient agar plate and 11 colonies on the glucose salts medium. Which of the following statements is INCORRECT? The prototrophs are resistant to penicillin but the auxotrophs are sensitive to this antibiotic. The colony that is missing from plate B is an auxotroph that cannot synthesize histidine. Prototrophs and auxotrophs in this experiment are resistant to penicillin. Approximately 92% of the bacteria in the original sample are prototrophs. This experiment describes indirect selection of a mutant.

The prototrophs are resistant to penicillin but the auxotrophs are sensitive to this antibiotic.

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 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. 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 have a stronger 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.

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. What concerns you most about the strain of H. influenzae that you may be exposed to while you are away is antibiotic resistance. The genes for resistance can be acquired by this organism as naked DNA from the environment, an example of: vertical gene transfer. conjugation. transduction. transformation. induced mutation.

Transformation

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. Which of the following statements is CORRECT regarding transformation? Transformation involves the formation of a sex pilus through which plasmid DNA is shared between bacteria. Transformation is the uptake of "naked" DNA from the environment. DNA is transferred from one bacterial cell to another by means of a bacteriophage. Transformation is a process that depends on physical contact between two bacterial cells. Transformation depends on a donor cell containing an F plasmid and a recipient cell that does not.

Transformation is the uptake of "naked" DNA from the environment.

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

Transposons

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

True

DNA polymerase is able to proofread the DNA sequence. True False

True

Each gene mutates at a characteristic frequency. True False

True

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

True

Mutations are likely to persist after SOS repair, but not after light-induced or excision repair. True False

True

Plasmids often carry the information for antibiotic resistance. True False

True

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

True

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? 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. 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, 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. This 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 change the hydrogen bonding properties of nucleotides. act during RNA 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.

act during DNA synthesis AND often result in frameshift mutations.

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

alkylating agents.

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

an F plasmid.

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

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

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

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

base analogs.

X-rays: cause thymine trimers. have no effect on DNA. 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 F+. transducers. mutants. F−. competent.

competent.

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

conjugation

Bacteria that have properties of both the donor and recipient cells are the result of genetic recombination. SOS repair. frame shift mutations. UV light. antibiotic resistance.

genetic recombination

Bacteria that have properties of both the donor and recipient cells are the result of: genetic recombination. SOS repair. frame shift mutations. UV light. antibiotic resistance.

genetic recombination.

Chemical mutagens often act by altering the nucleobases. alkyl groups of the nucleobase. hydrogen bonding properties of the nucleobase. number of binding sites on the nucleobase. nucleobase sequence.

hydrogen bonding properties of the nucleobase.

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

in both eukaryotes and prokaryotes.

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis. Your patient asks whether there is any way for him to get rid of this infection. You tell him that he will be given a different antibiotic such as doxycycline. This antibiotic works by binding to a cell structure called the 30S ribosomal subunit, which stops the bacterial cells from growing by preventing protein packaging. preventing DNA replication. stopping capsule formation. inhibiting protein synthesis. inhibiting transcription.

inhibiting protein synthesis.

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: integrate fragments from the phage RNA in their own chromosomes and target for destruction any RNA that contains the same fragments in the future. modify the attachment sites for the phages so that new infections cannot take place. 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.

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 antibiotic resistance AND allow populations to be measured. involve haploid chromosomes AND involve antibiotic resistance. involve polyploid chromosomes AND allow populations to be measured. use an indirect method for measurement AND involve antibiotic resistance. allow populations to be measured AND use an indirect method for measurement.

involve haploid chromosomes AND involve antibiotic resistance.

Indirect selection uses media upon which neither the parental cell type nor mutant grows. is necessary to isolate auxotrophic mutants. uses media that reverses the mutation. is necessary to isolate his+ prototrophs. uses media on which the mutant but not the parental cell type will grow.

is necessary to isolate auxotrophic mutants.

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

penicillin enrichment.

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

phenotype

Colonies of the bacterium Serratia marcescens are red when incubated at 22°C but white when incubated at 37°C. This is an example of: genotypic change. selective media. phenotypic change. antigenic variation. mutation.

phenotypic change.

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

provide an environment in which preexisting mutants survive.

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 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 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.

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

the mutant but not the parental cell type will grow

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

the sex pilus.

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

thymine dimers.

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis. You explain to your patient that there has been an increase in the number of strains of S. aureus that are now resistant to methicillin. The gene conferring resistance has moved from one strain to another via mobile gene elements, an example of which is a(n) ________. bacteriovirus insertional divider transposon histone chromosome

transposon

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

within the gene in question.