Deck 8: Bacterial Genetics

Question 1

Antibiotics

A) cause mutations to occur.
B) may act as alkylating mutagens.
C) provide an environment in which preexisting mutants survive.
D) increase the rate of spontaneous mutation.
E) destroy all mutant bacteria.

Answer 1

C

Question 2

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

A) phenotype.
B) genotype.
C) metabolism.
D) nucleoid.
E) plasmids.

Answer 2

A

Question 3

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

A) archaetype.
B) phenotype.
C) genotype.
D) mutatotype.
E) phenogene.

Answer 3

B

Question 4

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

A) base analogs.
B) intercalating agents.
C) transposons.
D) inverted repeats.
E) mutagens.

Question 5

The designation his⁻ refers to

A) the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine.
B) the genotype of bacteria that have a functional gene for histidine synthesis AND bacteria that require addition of histidine to the growth medium.
C) the genotype of bacteria that have a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine.
D) the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that have a hers gene.
E) 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.

Question 6

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

A) AATTAGTTC
B) AACCGGG
C) TATATACG
D) AUAUCGAU
E) TATATACG AND AATTAGTTC

Question 7

Thymine dimers are removed by

A) no repair mechanisms.
B) SOS repair AND photoreactivation repair.
C) SOS repair AND excision repair.
D) photoreactivation repair AND excision repair.
E) SOS repair, photoreactivation repair AND excision repair.

Question 8

X-rays

A) have no effect on DNA.
B) cause thymine trimers.
C) cause breaks in DNA molecules.
D) make the DNA radioactive.
E) destroy lipopolysaccharide.

Question 9

Irradiation of cells with ultraviolet light may cause

A) four nucleotides to covalently bind together.
B) thymine dimers.
C) adenine complementary base pairing with cytosine.
D) the addition of uracil.
E) cytosine trimers.

Question 10

The source of variation among microorganisms that were once identical is

A) antibiotic resistance.
B) virulence factors.
C) mutation.
D) sigma factors.
E) mutant.

Question 11

DNA repair mechanisms occur

A) only in prokaryotes.
B) only in eukaryotes.
C) in both eukaryotes and prokaryotes.
D) in neither eukaryotes nor prokaryotes.
E) None of the answer choices is correct.

Question 12

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

A) Deletion of two consecutive nucleotides
B) Addition of one nucleotide
C) Addition or deletion of three consecutive nucleotides
D) Substitution of one nucleotide AND addition of one nucleotide
E) Addition of two consecutive nucleotides

Question 13

Chemical mutagens often act by altering the

A) alkyl groups of the nucleobase.
B) nucleobase sequence.
C) number of binding sites on the nucleobase.
D) hydrogen bonding properties of the nucleobase.
E) nucleobases.

Question 14

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

A) X-rays.
B) alkylating agents.
C) UV radiation.
D) microwave radiation.
E) heat.

Question 15

Intercalating agents

A) act during RNA synthesis AND often result in frameshift mutations.
B) act during RNA synthesis AND change the hydrogen bonding properties of nucleotides.
C) act during DNA synthesis AND often result in frameshift mutations.
D) change the hydrogen bonding properties of nucleotides AND always result in nonsense mutations.
E) act during DNA synthesis AND always result in nonsense mutations.

Question 16

Which of the following about transposons is NOT True?

A) They are informally known as jumping genes.
B) They may cause insertion mutations.
C) They may cause knockout mutations.
D) They were first recognized in fungi.
E) All of the statements are True.

Question 17

Planar molecules used as chemical mutagens are called

A) intercalating agents.
B) nitrous oxide.
C) base analogs.
D) alkylating agents.
E) acids.

Question 18

Which is NOT True about mismatch repair?

A) It uses an endonuclease.
B) It requires DNA polymerase and DNA ligase.
C) It uses methylation of the DNA to differentiate between strands.
D) It removes both strands in the mismatch area.
E) It fixes errors missed by the proofreading of DNA polymerase.

Question 19

The largest group of chemical mutagens consists of

A) radiation.
B) alkylating agents.
C) nitrous acid.
D) base analogs.
E) intercalating agents.

Question 20

Chemical mutagens that mimic the naturally occurring bases are called

A) nitrogen mustards.
B) alkylating agents.
C) base analogs.
D) nitrous oxide.
E) nucleobase copiers.

Question 21

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

A) direct selection.
B) replica plating.
C) penicillin enrichment.
D) individual transfer.
E) mutant reversion.

Question 22

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

A) UV light.
B) SOS repair.
C) frame shift mutations.
D) genetic recombination.
E) antibiotic resistance.

Question 23

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

A) ellipsis.
B) transduction.
C) replica plating.
D) transformation.
E) conjugation.

Question 24

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

A) conjugation AND transformation.
B) conjugation AND transposons.
C) transformation AND transduction.
D) transduction AND transposons.
E) transformation AND transposons.

Question 25

Among the easiest of the mutations to isolate are those which

A) involve polyploid chromosomes AND allow populations to be measured.
B) involve antibiotic resistance AND allow populations to be measured.
C) allow populations to be measured AND use an indirect method for measurement.
D) involve haploid chromosomes AND involve antibiotic resistance.
E) use an indirect method for measurement AND involve antibiotic resistance.

Question 26

Competent cells

A) are able to take up naked DNA, can be created in the laboratory, AND are always antibiotic resistant.
B) are able to take up naked DNA, occur naturally, AND can be created in the laboratory.
C) are always antibiotic resistant, are always auxotrophs, AND occur naturally.
D) can be made in the laboratory, are always antibiotic resistant, AND are always auxotrophs.
E) are able to take up naked DNA, occur naturally, AND are always antibiotic resistant.

Question 27

The material responsible for transformation was shown to be DNA by

A) Watson and Crick.
B) Avery, MacLeod, and McCarty.
C) Lederberg.
D) Stanley.
E) Beadle and Tatum.

Question 28

Direct selection involves inoculating cells onto growth media on/in which

A) the mutant but not the parental cell type will grow.
B) the mutation will be reversed.
C) the nutrients necessary for mutation to occur are present.
D) the mutagen is present.
E) histidine has been added.

Question 29

Replica plating

A) is useful for direct selection of antibiotic resistance AND is useful for identifying auxotrophs.
B) uses media on which the mutant will grow but the parental cell type will not AND is useful for identifying prototrophs.
C) is useful for identifying auxotrophs AND uses media on which the mutant will not grow but the parental cell type will.
D) is useful for identifying auxotrophs AND uses media on which the mutant will grow but the parental cell type will not.
E) is useful for direct selection of antibiotic resistance AND is useful for identifying prototrophs.

Question 30

Insertion sequences

A) are the simplest type of transposon, code for a transposase enzyme AND can produce pili.
B) code for a transposase enzyme AND are characterized by an inverted repeat.
C) are characterized by an inverted repeat AND can produce pili.
D) can produce pili AND are the simplest type of transposon.
E) are the simplest type of transposon, code for a transposase enzyme, AND are characterized by an inverted repeat.

Question 31

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

A) penicillin.
B) heat.
C) ground-up rat liver.
D) reverse transcriptase.
E) penicillin AND heat.

Question 32

A quick microbiological test for potential carcinogens was developed by

A) Fleming.
B) Lederberg.
C) Ames.
D) Crick.
E) McClintock.

Question 33

The F plasmid carries the information for

A) the sex pilus.
B) recipient cell DNA replication.
C) antibiotic resistance.
D) the Y chromosome.
E) bacterial flagella.

Question 34

Indirect selection

A) is necessary to isolate auxotrophic mutants.
B) uses media on which the mutant but not the parental cell type will grow.
C) uses media that reverses the mutation.
D) uses media upon which neither the parental cell type nor mutant grows.
E) is necessary to isolate his⁺ prototrophs.

Question 35

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

A) will respond to chemical agents.
B) are mutagens.
C) respond to the deletion of DNAses.
D) will protect an organism from cancer.
E) will respond to chemical agents AND will protect an organism from cancer.

Question 36

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

A) from any source.
B) from any species of bacteria.
C) from the same species of bacteria.
D) only through plasmids.
E) from any source AND only through plasmids.

Question 37

Gene transfer that requires cell-to-cell contact is

A) transformation.
B) competency.
C) conjugation.
D) functional genomics.
E) transduction.

Question 38

A clever technique that streamlines the identification of auxotrophic mutants is

A) gas chromatography.
B) replica plating.
C) direct selection.
D) reversion.
E) intercalation.

Question 39

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

A) the matching chromosome may carry the correct version of the gene.
B) the matching chromosome may repair the mutated gene.
C) the mutation is usually reversible.
D) the mutation may create inverted repeats.
E) All answer choices are correct.

Question 40

In conjugation the donor cell is recognized by the presence of

A) an F plasmid.
B) a Y chromosome.
C) diploid chromosomes.
D) an SOS response.
E) an F plasmid AND diploid chromosomes.

Question 41

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?

A) The dark-light will activate the photorepair systems that can break thymine dimers induced by UV light.
B) The light-it's important to keep on producing the thymine dimers by keeping the plate exposed to light as much as possible.
C) 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.
D) It doesn't matter-human cells don't have the enzymes needed for photorepair of thymine dimers.
E) Alternating light and dark every 24 hours to increase the chances that thymine dimers will form.

Question 42

Double-stranded DNA enters the recipient cell during transformation.

Question 43

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

Question 44

DNA is protected from restriction enzymes by being

A) sequestered in a lysosome.
B) turned into RNA.
C) methylated.
D) made into double-stranded RNA.
E) phosphorylated.

Question 45

Each gene mutates at a characteristic frequency.

Question 46

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

Question 47

DNA polymerase is able to proofread the DNA sequence.

Question 48

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?

A) 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).
B) 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.
C) 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).
D) Trick question-it can take place with the same degree of efficiency on either format. It doesn't matter!
E) 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.

Question 49

The study of the crown gall tumor found

A) a bacterial plasmid promoter that was similar to plant promoters.
B) an R plasmid in plant cells.
C) incorporation of the bacterial chromosome into the plant.
D) incorporation of the plant chromosome into the bacteria.
E) a bacterial plasmid promoter that was similar to plant terminators.

Question 50

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

Question 51

Plasmids often carry the information for antibiotic resistance.

Question 52

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

A) Good-kill those cancer cells as quickly as possible to cure the patient!
B) Bad-these mutagens will also affect the non-cancerous cells, possibly leading to new cancerous states!
C) Good and bad-they're very good at killing cancer cells, but they could also be dangerous to non-cancerous cells.
D) Bad-the cancer cells are already mutated. We don't want to mutate them more and make them more cancerous!
E) Bad-the medications are toxic and will cause healthy normal microbiots to become cancerous.

Question 53

Organisms termed his⁻ are considered prototrophic for histidine.

Question 54

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

Question 55

The Ames test determines antibiotic sensitivity of a bacterium.

Question 56

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?

A) Proofreading by DNA polymerase, glycosylase enzyme activities, excision repair, SOS repair
B) SOS repair, excision repair, glycosylase enzyme activities, proofreading by DNA polymerase
C) SOS repair, proofreading by DNA polymerase, glycosylase enzyme activities, excision repair
D) Glycosylase enzyme activities, SOS repair, proofreading by DNA polymerase, excision repair
E) Proofreading by DNA polymerase, SOS repair, glycosylase enzyme activities, excision repair

Question 57

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) 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.
B) 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.
C) 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.
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) 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.

Question 58

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.

Question 59

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

A) 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!
B) 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.
C) 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.
D) 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.
E) 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.

Question 60

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?

A) 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.
B) 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.
C) 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.
D) They may have a stronger expression of photoreactivation enzymes, leading to more thymine dimers being formed and retained.
E) They may have a weaker expression of photoreactivation enzymes, leading to more thymine dimers being formed and retained.

Question 61

Which of the following statements about spontaneous mutation is True?

A) A single mutation is common but a double mutation is very rare.
B) 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.
C) 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.
D) 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.
E) A transposon may insertionally inactivate a gene when it jumps from one place in a genome to another.

Question 62

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 

A) preventing DNA replication.
B) inhibiting transcription.
C) stopping capsule formation.
D) inhibiting protein synthesis.
E) preventing protein packaging.

Question 63

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) ________.

A) bacteriovirus
B) insertional divider
C) histone
D) transposon
E) chromosome

Question 64

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?

A) 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.
B) 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.
C) 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.
D) No-transduction efficiency isn't affected by either restriction endonucleases or modification enzymes, so there'd be no effect on the overall rate.
E) 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.

Question 65

In order for insertional inactivation to occur, the transposon must be placed

A) upstream from the gene in question.
B) downstream from the gene in question.
C) within the gene in question.
D) randomly in the genome.
E) in an intron.

Question 66

Further tests indicate that your patient has a methicillin-resistant Staphylococcus aureus (MRSA) infection. You explain to the patient that these bacteria are not impacted by penicillin or the related drug methicillin. This resistance is thought to have arisen originally by a random change in the cell's chromosome through a process called 

A) spontaneous mutation.
B) antigenic variation.
C) quorum sensing.
D) vertical gene transfer.
E) indirect selection.

Question 67

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

A) conjugation.
B) transformation.
C) induced mutation.
D) vertical gene transfer.
E) transduction.

Question 68

Cells that are His⁻, Strᴿ could be isolated from a mixed sample by using a medium containing

A) streptomycin
B) histidine AND glucose
C) penicillin AND streptomycin
D) glucose AND streptomycin
E) histidine AND streptomycin

Question 69

Which of the following statements is CORRECT regarding transformation?

A) DNA is transferred from one bacterial cell to another by means of a bacteriophage.
B) Transformation is the uptake of "naked" DNA from the environment.
C) Transformation involves the formation of a sex pilus through which plasmid DNA is shared between bacteria.
D) Transformation depends on a donor cell containing an F plasmid and a recipient cell that does not.
E) Transformation is a process that depends on physical contact between two bacterial cells.

Question 70

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 

A) antigenic variation.
B) genotypic change.
C) phenotypic change.
D) mutation.
E) selective media.

Question 71

H. influenzae has genes that it needs to make pili for attachment to host cells. These pili genes are not always expressed; sometimes the bacterium turns them off and does not produce pili. This is an example of 

A) phase variation.
B) antigenic sensing.
C) two-component control.
D) transduction.
E) gene splicing.

Question 72

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.

A) Escherichia; Gram-negative
B) Streptococcus; Gram-positive
C) Staphylococcus; Gram-positive
D) Streptobacillus; Gram-positive
E) Vibrio; Gram-negative

Question 73

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?
A) The colony that is missing from plate B is an auxotroph that cannot synthesize histidine.

A) that contains histidine and penicillin. The other is a glucose salts agar (plate
B) The prototrophs are resistant to penicillin but the auxotrophs are sensitive to this antibiotic.
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?
C) Prototrophs and auxotrophs in this experiment are resistant to penicillin.

Question 74

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?

A) The patient has become resistant to penicillin and he needs to take a different medication.
B) The bacteria causing the infection are resistant to penicillin; a different antibiotic is needed.
C) Bacteria are never killed by a single type of antibiotic; combinations of drugs are needed.
D) Penicillin has been overused by people and it no longer works against any bacteria; it can be used against viruses.
E) The patient's body is neutralizing the antibiotic; he needs to take a probiotic to help the penicillin work.

Question 75

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

Question 76

Please select the INCORRECT statement regarding mutation.

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

Question 77

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?

A) The bacteria in the colonies are His−, Val−, Trp⁺, Leu⁺.
B) The bacteria in the colonies are His−, Val⁺, Trp⁺, Leu⁺.
C) The bacteria in the colonies are His−, Val−, Trp−, Leu−.
D) The bacteria in the colonies are His⁺, Val⁺, Trp⁺, Leu⁺.
E) The bacteria in the colonies are His⁺, Val⁺, Trp⁺, Leu⁺, Penᴿ.

Question 78

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

A) recognize proteins on the surface of the phage and secrete enzymes that digest the phage.
B) recognize proteins on the surface of the phage and secrete proteins that block the binding of the phage.
C) integrate fragments from the phage DNA in their own chromosomes and target for destruction any DNA that contains the same fragments in the future.
D) modify the attachment sites for the phages so that new infections cannot take place.
E) integrate fragments from the phage RNA in their own chromosomes and target for destruction any RNA that contains the same fragments in the future.

Question 79

A bacterial strain is resistant to infection by a bacteriophage. Which statement is False?

A) The bacteria make restriction enzymes that degrade the virus genome.
B) The bacterial host DNA is protected from restriction enzyme degradation by phosphorylation.
C) The bacterial host DNA is protected from restriction enzyme degradation by methylation.
D) If the phage DNA was methylated, it would be protected from restriction enzyme degradation.
E) The statements are ALL False.

Question 80

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?

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