Ch13 test file

Chapter 13: The Genetics of Viruses and Prokaryotes

TEST FILE QUESTIONS

Multiple Choice

1. Which of the following statements about “bird flu” is false?

a. It is caused by a virus.

b. It can be transmitted from birds to humans.

c. Killing infected birds has prevented widespread occurrence of the disease.

d. It causes fever, coughing, and lung failure.

e. It is found only in birds.

Textbook Reference: 13.0 Mutation of a Bird Virus results in Human Infection, p. 282

2. Which of the following statements about viruses is true?

a. They are acellular.

b. They can regulate the movements of substances into and out of the cell.

c. They can reproduce outside of living cells.

d. They are large and therefore easy to study.

e. They are readily destroyed by antibiotics.

Textbook Reference: 13.1 How Do Viruses Reproduce and Transmit Genes? p. 283

3. Prokaryotes and viruses are useful for the study of genetics and molecular biology

because

a. they contain much less DNA than do eukaryotes.

b. they grow and reproduce rapidly.

c. they are haploid.

d. Both a and b

e. All of the above


4. Which of the following is not one of the advantages of working experimentally with

bacteria instead of mice?

a. Bacteria have a smaller amount of DNA.

b. Bacteria are nonpathogenic.

c. Bacteria reproduce very rapidly.

d. Bacteria are easy to grow.

e. Bacteria are usually haploid.


5. Viruses were first discovered in 1892 when

a. a filtrate was found to be infectious.

b. Albert Virusa became ill from smoking infected tobacco.

c. Stanley found that crystallized viral preparations contained protein and DNA.

d. they were first observed using a light microscope.

e. they were observed as plaques for the first time.


6. The scientist who first crystallized tobacco mosaic virus was

a. Dmitri Ivanovsky.

b. Martinus Beijerinick.

c. Jackson Robertson.

d. Wendell Stanley.

e. Rosalind Franklin.


7. Viruses are

a. cells containing DNA and protein.

b. larger than most bacteria.

c. acellular.

d. able to take in nutrients and expel wastes.

e. mutated forms of DNA.


8. Viruses are composed of

a. nucleic acids only.

b. proteins only.

c. nucleic acids and proteins.

d. nucleic acids, proteins, and organelles.

e. nucleic acids and proteins, although a few also have organelles.


9. Viruses

a. arise from preexisting viruses.

b. replicate their DNA before they reproduce.

c. develop and reproduce only within the cells of hosts.

d. have ribosomes that synthesize needed proteins.

e. cannot replicate.


10. A virion consists of

a. a capsid and a nucleic acid genome.

b. a promoter and RNA polymerase.

c. RNA and R factors.

d. a small bacterial chromosome.

e. plasmids that carry genes for antibiotic resistance.


11. A virus differs from a bacterium in that it

a. is not affected by antibiotics.

b. is composed of nucleic acids only.

c. is man-made.

d. has both protein and nucleic acid.

e. All of the above


12. The genetic information of viruses is

a. DNA.

b. RNA.

c. single-stranded.

d. double-stranded.

e. All of the above


13. Antibiotics are ineffective as treatments against viruses because

a. viruses can remain inactive until the antibiotic disintegrates.

b. viruses may reproduce immediately and destroy the antibiotic.

c. viruses have RNA instead of DNA.

d. viruses do not have either a cell wall or the ribosomal biochemistry of bacteria.

e. the nucleic acid of viruses is single-stranded rather than double-stranded.


14. The term “lysogeny” refers to

a. the stable integration of bacteriophage DNA into the bacterial chromosome.

b. the excision of bacteriophage DNA from the bacterial chromosome.

c. the lysing of a bacterium by a bacteriophage.

d. mutation induced by a bacteriophage.

e. exchange of genetic material between a bacteriophage and a bacterium.


15. A virion with a lipid and protein membrane (capsid) is likely to infect

a. animal cells.

b. plant cells.

c. bacteria.

d. fungi.

e. All of the above


16. Which of the following statements about the lytic cycle is true?

a. The phage DNA integrates into the bacterial chromosome.

b. Temperate viruses are formed.

c. Prophages are replicated.

d. The host cell lyses.

e. Immunity to a specific strain of phage may result.


17. Lysis of the host cell is caused by

a. the cell’s bursting due to the large number of viral particles.

b. the cell’s opening up in an attempt to release the viruses.

c. an attack on the cell wall by a product of the viral gene.

d. an as yet unknown mechanism.

e. None of the above


18. A strain of virus that reproduces only by the lytic cycle is called

a. temperate.

b. virulent.

c. lytic.

d. lysogenic.

e. deadly.


19. A patient who is told that he has contracted a disease caused by an arbovirus most

likely

a. contracted the virus from food.

b. had physical contact with an infected person.

c. contracted the virus from an insect.

d. contracted the virus from pet feces.

e. can spread the disease to others.


20. The HIV virus that causes AIDS is a(n)

a. arbovirus.

b. double-stranded DNA virus.

c. single-stranded DNA virus.

d. porcine virus.

e. retrovirus.


21. The influenza virus and the HIV virus differ in that only the influenza virus can

a. produce and use reverse transcriptase.

b. use RNA as its genetic material.

c. use RNA as genetic information and mRNA without generating a DNA molecule.

d. infect both horses and humans.

e. All of the above


22. The retrovirus HIV enters a host cell

a. by fusion of its envelope with the host’s plasma membrane.

b. by endocytosis.

c. by vectors.

d. through cytoplasmic connections between cells (plasmodesmata).

e. by phagocytosis.


23. Plants have a tough cell wall through which viruses cannot pass. Viruses enter plants

primarily

a. through openings called stomata.

b. by means of insect vectors.

c. by digesting the cell wall.

d. Both a and b

e. Both b and c


24. Once inside a plant cell, viruses spread by

a. diffusion.

b. Brownian motion.

c. plasmodesmata.

d. attaching to a shared endoplasmic reticulum.

e. the movement of rainwater.


25. The determination of whether a temperate phage undergoes a lytic or a lysogenic

cycle depends on the

a. presence or absence of protein CD4.

b. cellular environment of the host.

c. presence or absence of plasmodesmata.

d. nucleotide sequences of the phage.

e. size of the genome.

Textbook Reference: 13.2 How Is Gene Expression Regulated in Viruses? p. 290

26. The effects of Cro and cI on bacteriophage are

a. competitive.

b. cooperative.

c. coordinate.

d. inverted.

e. additive.


27. Beginning with a single bacterium, how many cells would be present after four hours

of growth if they can double every 20 minutes?

a. 12

b. 24

c. 64

d. 4,096

e. 34,217,728

Textbook Reference: 13.3 How Do Prokaryotes Exchange Genes? p. 290

28. A population of genetically identical bacteria that arose from a single cell is known as

a

a. plaque.

b. lysogen.

c. clone.

d. bacterial culture.

e. conjugation.


29. The term “auxotroph” refers to

a. a mutant bacterium that requires nutrients not required by wild-type bacteria.

b. a mutant bacterium that requires no nutrients.

c. a mutant bacterium that can synthesize a nutrient that wild-type bacteria cannot.

d. a mutant bacterium that can metabolize a nutrient that wild-type bacteria cannot.

e. a bacterium that can metabolize sugars.


30. When a met– bio– strain of bacteria is mixed with a thr– leu– strain, wild-type bacteria

result at the rate of one in every 107 cells. Why is it not possible for the wild-type bacteria

to be the result of a mutation?

a. The wild type would have to be a double mutation, which is extremely rare.

b. The wild type would have to be a mutation in four genes, which is extremely rare.

c. The wild type would have to be a deletion, which is extremely rare.

d. Mutations can occur only in response to a mutagen.

e. Bacterial genes do not mutate.


31. The met+leu+ bacteria that result from a cross between met+leu– and met–leu+ bacteria

are the result of

a. transformation.

b. chance.

c. mutation.

d. genetic recombination.



32. Genetic diversity in a bacterial population comes about due to

a. conjugation.

b. transformation.

c. transduction.

d. genetic recombination.

e. All of the above

Textbook Reference: 13.3 How Do Prokaryotes Exchange Genes? pp. 291–292

33. Which of the following is not a mechanism of bacterial genetic recombination?

a. Transformation

b. Conjugation

c. Transduction

d. Catabolite repression

e. Both a and b


34. The function of the pili is to

a. store the F plasmid.

b. make the initial contact between an F+ and an F– cell that precedes conjugation.

c. uptake DNA during transformation.

d. transfer the DNA between mating partners during conjugation.



35. The transfer of genes by uptake of DNA from dead organisms characterizes which

type of gene transfer in bacteria?

a. Conjugation

b. Transference

c. Transduction

d. Transformation


Textbook Reference: 13.3 How Do Prokaryotes Exchange Genes? pp. 292, 293

36. The transfer of genes by a bacteriophage vector characterizes which type of gene

transfer in bacteria?

a. Transformation

b. Conjugation

c. Transduction

d. Transference



37. In transduction,

a. only a particular part of the bacterial chromosome can be transferred.

b. a part of the bacterial chromosome may be transferred.

c. only the F plasmid can be transferred.

d. only the part of the bacterial chromosome near the F plasmid can be transferred.



38. All plasmids

a. are integrated into the bacterial chromosome.

b. have an R factor.

c. have a capsid.

d. have an origin of replication.

e. All of the above


39. What is the difference between a plasmid and a transposable element?

a. Plasmids exist in many copies in the cell, whereas a transposable element exists in a

single copy.

b. A plasmid replicates independently of the cell; a transposable element does not.

c. A plasmid has an origin of replication; a transposable element does not.

d. A plasmid exists independently in the cell cytoplasm, whereas a transposable element

is integrated into a larger DNA molecule.



40. An R factor is a(n)

a. plasmid that carries genes for antibiotic resistance.

b. episome that carries genes for antibiotic resistance.

c. region of the bacterial chromosome that carries genes for antibiotic resistance.

d. small portion of the F plasmid.

e. measure of how well the bacterium is insulated from the cold.


41. Which of the following statements about the F plasmid is false?

a. It can integrate itself into the main chromosome.

b. It can be transferred from a donor to a recipient bacterium during mating.

c. It is involved in conjugation.

d. It contains approximately 25 genes.

e. It contains genes that encode antibiotic resistance.


42. Both F plasmids and bacteriophage

a. have a protein coat enclosing the DNA.

b. can lyse bacteria.

c. can participate in conjugation.

d. can incorporate themselves into the bacterial chromosome.

e. Both a and b


43. Which of the following statements about conjugation between an F– bacterium and an

F+ bacterium is false?

a. A conjugation tube is formed between the two bacteria.

b. The F+ cell transfers a copy of the F plasmid to the F– cell.

c. The F– cell receives a copy of the F plasmid.

d. The F– cell becomes F+.

e. The F+ cell becomes F–.


44. R factors, or resistance factors, carried by plasmids or bacteria are more widely

detected now than in the past because

a. the heavy use of antibiotics has stimulated the evolution of R factors.

b. techniques for detection have improved.

c. current bacterial culture conditions favor the selection of R factors.

d. Both a and c



45. The occurrence of resistant bacteria is expected to increase. Resistant bacteria are the

result of

a. universal gene segments that have been copied many times.

b. natural selection due to increased use of antibiotics.

c. transposons that have inserted themselves into a gene, causing mutation.

d. parasites that grow and take control of normal cell activities.

e. a gene deficiency for the electron transport chain.


46. Genetic diversity is introduced into bacterial populations through

a. conjugation.

b. transformation.

c. transduction.

d. the acquisition of new genes via plasmids and transposable elements.

e. All of the above


47. The most efficient means of regulating protein synthesis is by

a. selective blocking of transcription.

b. translation of the mRNA.

c. inhibition of the protein.

d. degradation of the protein.

e. transcription of the gene.

Textbook Reference: 13.4 How Is Gene Expression Regulated in Prokaryotes? p. 296

48. When E. coli are grown in a medium with little lactose,

a. all of the enzymes of the lactose operon are present in very small quantities.

b. all of the enzymes of the lactose operon are present in large quantities.

c. no enzymes of the lactose operon are present.

d. -galactosidase and permease are present in small quantities, but transacetylase is

present in large quantities.

e. the mRNA of the lactose operon is not present at all.


49. A cell can control the amount of enzymes it produces by

a. blocking transcription.

b. hydrolyzing the mRNA.

c. preventing translation.

d. hydrolyzing the protein.

e. All of the above


50. Research on E. coli indicates that

a. lactose is the preferred energy source.

b. glucose is the preferred energy source.

c. lactose and glucose are used equally as an energy source.

d. -galactosidase is required for glucose metabolism.

e. three different proteins are synthesized when glucose is present.


51. A promoter is the region of

a. a plasmid that binds the enzymes for replication.

b. the mRNA that binds to a ribosome.

c. DNA that binds RNA polymerase.

d. the mRNA that binds tRNAs.



52. The lac operon of E. coli consists of

a. a segment of DNA.

b. a promoter.

c. an operator.

d. three structural genes.

e. All of the above


53. The three basic parts of an operon are the

a. promoter, the operator, and the structural gene(s).

b. promoter, the structural gene(s), and the termination codons.

c. promoter, the mRNA, and the termination codons.

d. structural gene(s), the mRNA, and the tRNAs.



54. The RNA transcribed from an operon is

a. transcribed by the ribosomes to make more repressor.

b. translated by the ribosomes to make more inducer.

c. translated by the ribosomes to make the enzymes.

d. translated by the ribosomes to make more RNA polymerase.

e. usually not translated by the ribosomes at all.


55. The function of the promoter is to tell the RNA polymerase

a. where to start transcribing the DNA.

b. which strand of the DNA to read.

c. where to stop transcribing the DNA.

d. Both a and b

e. All of the above


56. The mechanism by which the inducer causes the repressor to detach from the operator

is an example of

a. catabolite repression.

b. transcription.

c. transposition.

d. allosteric modification.

e. recombination.


57. _______ acts as a corepressor to block transcription of the tryptophan operon.

a. cAMP

b. Lactose

c. Tryptophan

d. Methionine

e. CRP


58. The frequency of transcription of a particular bacterial gene is controlled by the

a. DNA sequence of the particular promoter.

b. availability of the promoter to RNA polymerase.

c. number of ribosomes that are available in the cell.

d. Both a and b

e. All of the above


59. An inducer

a. combines with a repressor and prevents it from binding the promoter.

b. combines with a repressor and prevents it from binding the operator.

c. binds to the promoter and prevents the repressor from binding to the operator.

d. binds to the operator and prevents the repressor from binding at this site.

e. binds to the termination codons and allows protein synthesis to continue.


60. The genes that encode repressor proteins are

a. repressor genes.

b. operons.

c. inducer genes.

d. regulatory genes.



61. Which operon is turned “off” in response to molecules present in the environment of

the cell?

a. Repressible

b. Suppressible

c. Impressible

d. Inducible

e. Degraded


62. In a repressible operon, the repressor molecule

a. must first be activated by a corepressor.

b. can repress the transcription of the operon on its own.

c. is a molecule made from the operon.

d. binds to the mRNA.

e. must first be made negative to control the operon.


63. It is found that a certain enzyme is synthesized whenever the solution in which the

cells are growing lacks substance X. This phenomenon is most likely an example of

_______ gene regulation.

a. inducible

b. positive

c. negative

d. repressible

e. positive–negative


64. It is found that a certain enzyme is synthesized whenever the solution in which the

cells are growing contains substance X. This phenomenon is most likely an example of

_______ gene regulation.

a. inducible

b. positive

c. negative

d. repressible

e. positive–negative


65. The trp operon

a. codes for proteins needed for tryptophan synthesis.

b. codes for proteins needed to metabolize tryptophan.

c. is activated by the presence of tryptophan.

d. is inducible.

e. All of the above


66. The CRP–cAMP complex binds _______ of the operon.

a. close to the RNA polymerase binding site

b. close to the operator

c. inside one of the structural genes

d. at the termination point



67. How are inducible and repressible systems similar?

a. They both control catabolic pathways.

b. They both control biosynthetic pathways.

c. In both systems the regulatory molecules function by binding to the operator.

d. They both block transcription.

e. Both systems are unique to prokaryotes.


68. Catabolite repression refers to the

a. increased transcription from many operons when glucose is present in the medium.

b. shutdown of transcription from many operons when glucose is present in the medium.

c. increased activity of inducers caused by glucose in the medium.

d. Both a and b

e. Both a and c


69. To be activated, the CRP must first bind

a. the repressor molecule.

b. the repressor protein.

c. the activator protein.

d. the corepressor molecule.

e. cAMP.


70. When the operator is unbound, the binding of the CRP–cAMP complex _______ the

binding of RNA polymerase at the promoter.

a. prevents

b. decreases

c. increases

d. blocks

e. All of the above are sometimes true, depending on the concentration of lactose.


71. When the concentration of glucose is high, the concentration of _______ is low.

a. CRP

b. cAMP

c. repressors

d. inducers



72. What effect does the presence of ample glucose have on the amount of lac operon

transcription?

a. It increases the cAMP concentration, which in turn causes a decreased rate of

transcription.

b. It decreases the cAMP concentration, which in turn causes an increased rate of

transcription.

c. It increases the rate of transcription.

d. It decreases the rate of transcription.



73. Commonly used antibiotics such as streptomycin, tetracycline, and erythromycin are

produced by

a. Chlamydia trachomatis.

b. Rickettsia prowazekii.

c. Mycobacterium tuberculosis.

d. Streptomyces coelicolor.

e. E. coli.

Textbook Reference: 13.5 What Have We Learned from the Sequencing of Prokaryotic

Genomes? p. 302

74. The minimum number of genes necessary for a life form grown in laboratory

conditions is

a. 48.

b. 337.

c. 470.

d. 3,876.

e. 10,082.


Genomes? p. 303

Fill in the Blank

1. The first virus that was discovered was the _______ virus.


2. An individual viral particle is known as a(n) _______ when it is outside its host.


3. The basic viral unit is the _______.


4. Bacteria that house nonlytic bacteriophage are called _______ bacteria.


5. Bacteriophage DNA that is stably integrated into a bacterial chromosome is called a

_______.


6. Viruses that can integrate their DNA into the host bacterial chromosome are called

_______.


7. A _______ consists of complementary DNA transcribed from an RNA genome.


8. _______ are nonessential genetic elements that exist as free, independently replicating,

circular DNA molecules, separate from the bacterial chromosome.


9. The plasmids that encode the genes needed for conjugation are called _______.


10. Pieces of DNA that move from place to place in the bacterial chromosome are called

_______.


11. Antibiotics are ineffective against _______ infections.


12. Antibiotic resistance in pathogenic bacteria is an example of _______.


13. Genes that specify the primary structure of a protein are called _______ genes.


14. The operon containing the genes for the three lactose-metabolizing proteins of E. coli

is called the _______ operon.


15. Genes that produce single mRNAs containing information for more than one protein

are called _______.


16. The region of the gene that binds RNA polymerase is the _______.


17. The site on the operon DNA where a repressor binds is called the _______ sequence.


18. In prokaryotes, _______ genes encode repressor proteins.


19. When the synthesis of an enzyme is turned off in response to an external biochemical

cue (such as an excess in tryptophan), the enzyme is said to be _______.


20. A positive control process that relies on increasing the affinity of promoters for RNA

polymerase is called _______.


21. The relatively new field of _______ is concerned with studying the comparative

genome sequences of different organisms.


Genomes? p. 301

22. Genes that are present in all organisms are referred to as _______ genes.


Genomes? p. 302

Diagram

1. Refer to the diagram below of gene transfer by plasmids to answer the question that

follows.

The largest arrow is pointing to a(n)

a. plasmodesma.

b. conjugation tube.

c. stomate.

d. vector.

e. operon.


STUDY GUIDE QUESTIONS

Knowledge and Synthesis Questions

1. Viruses consist of

a. a protein core and a nucleic acid capsid.

b. a cell wall surrounding nucleic acid.

c. RNA and DNA enclosed in a membrane.

d. a nucleic acid core surrounded by a protein capsid and in some cases a membrane.


2. Bacterial cells that are resistant to viruses

a. lack a cell surface receptor that the virus must bind to infect the cell.

b. harbor a prophage in their chromosome, making the bacterial cell immune to further

viral infection.

c. cannot be lysed by the bacteriophage.

d. All of the above


3. Lytic bacterial viruses

a. infect the cell, replicate their genomes, and lyse the cell.

b. infect the cell, replicate their genomes, transcribe and translate their genes, and lyse the

cell.

c. infect the cell, replicate their genomes, transcribe and translate their genes, package

those genomes into viral capsids, and lyse the cell.

d. infect the cell, translate their RNA, and lyse the cells.

Textbook Reference: 13.1 How Do Viruses Reproduce and Transmit Genes? p. 285,

Figure 13.3

4. Animal viruses that integrate their DNA into the host chromosome

a. are RNA viruses.

b. are prophages.

c. copy their RNA genome into DNA using reverse transcriptase.

d. Both a and c


5. During conjugation,

a. DNA from one bacterial cell is transferred to another bacterial cell using a

bacteriophage.

b. mutants that are auxotrophic for one nutrient can be converted to prototrophs when

mixed with mutants that are auxotrophic for another nutrient.

c. a pilus is synthesized, and DNA is transferred from one bacterium across the

conjugation tube to the recipient bacterium.

d. Both b and c


6. Plasmid DNA may contain genes that can

a. confer drug resistance to the host cell.

b. regulate conjugation.

c. confer resistance to heavy metals.

d. All of the above


7. An operon

a. is regulated by a repressor binding at the promoter.

b. has structural genes that are all transcribed from same promoter.

c. has several promoters, but all of the structural genes are related biochemically.

d. is a set of structural genes all under the same translational regulation.


8. If the gene encoding the lac repressor is mutated so that the repressor can no longer

bind the operator, will transcription of that operon occur?

a. Yes, but only when lactose is present.

b. No, because RNA polymerase is needed to transcribe the genes.

c. Yes, because RNA polymerase will be able to bind the promoter and transcribe the

operon.

d. No, because cAMP levels are low when the repressor is nonfunctional.

Textbook Reference: 13.4 How Is Gene Expression Regulated in Prokaryotes? pp. 297–

298

9. If the gene encoding the trp repressor is mutated such that it can no longer bind

tryptophan, will transcription of the trp operon occur?

a. Yes, because the trp repressor can only bind the trp operon and block transcription

when it is bound to tryptophan.

b. No, because this mutation does not affect the part of the repressor that can bind the

operator.

c. No, because the trp operon is repressed only when tryptophan levels are high.

d. Yes, because the trp operon can allosterically regulate the enzymes needed to

synthesize the amino acid tryptophan.


10. Transcriptional regulation in prokaryotes can occur by

a. a repressor binding an operator and preventing transcription.

b. an activator binding upstream from a promoter and positively affecting transcription.

c. different promoter sequences binding RNA polymerase more tightly, resulting in more

effective transcriptional initiation.

d. All of the above

Textbook Reference: 13.4 How Is Gene Expression Regulated in Prokaryotes? pp. 297–

299

11. Functional genomics

a. assigns function to the products of genes.

b. assigns functions to regulatory sequences.

c. compares genes in different organisms to see how the how those organisms are related

physiologically.

d. All of the above


Genomes? pp. 301–303

12. Comparative genomics

a. assigns function to the products of genes.

b. assigns functions to regulatory sequences.

c. compares genes in different organisms to see how the how those organisms are related

physiologically.

d. All of the above



13. A transposon is used to inactivate genes in a bacterium. If the inactivated gene is

essential the bacterium will

a. live.

b. die.

c. be a prototroph.

d. be resistant to viral infection.



14. In order to infect a plant, plant viruses must

a. pass through the cell wall as well as the plasma membrane.

b. utilize an insect vector to travel from plant to plant.

c. spread through the plasmodesmata between cells.

d. All of the above


15. For the bacteriophage , the decision to become a prophage is made

a. if environmental resources (i.e. food) for the host are limiting.

b. when the Cro protein binds the promoter.

c. when the CI protein binds the promoter.

d. when bacterial lysis occurs.


Application Questions

1. Animal viruses are oblgate parasites. What does this mean?

Textbook Reference: 13.1 How Do Viruses Reproduce and Transmit Genes? pp. 284–285

2. Why are antibiotics useless in combating animal viral infections?


3. Genomics has revealed that the bacterium that causes tuberculosis has over 250 genes

that metabolize lipids. What does this finding suggest about the bacterium and about

medicinal approaches to this disease?


Genomes? p. 302

4. A cell has a mutation that deletes the gene encoding the repressor for a certain operon.

A plasmid is introduced into the host cell that carries a wild-type copy of the gene for the

repressor. Is normal regulation of this operon restored in the presence of this plasmid?


5. A cell has a mutation that deletes the gene encoding the operator for a certain operon.

A plasmid is introduced into the host cell that carries a wild-type copy of the operator. Is

normal regulation of this operon restored in the presence of this plasmid?


6. Review some of the auxotrophic bacterial strains that Lederberg and Tatum were

studying. Describe three different ways that an auxotrophic bacterium can be converted to

a prototrophic bacterium.


ONLINE QUIZ QUESTIONS

1. Which human pathogen has 634 genes, six coding for proteins that are essential to its

virulence?

a. Streptomyces coelicolor

b. Chlamydia trachomatis

c. E. coli

d. Rickettsia prowazekki

e. Mycobacterium tuberculosis


Genomes? p. 301

2. In the lytic cycle of a bacteriophage,

a. infection does not always result in lysis of the host cell.

b. the viral genome contains a promoter sequence that attracts host DNA polymerase.

c. only the early phage genes are transcribed.

d. only the late phage genes are transcribed.

e. premature lysis of the host cell before virions are ready for release would stop the

infection.


3. If there is lactose present in the cell, the lac operon is, not able to transcribe the lac

structural genes.

a. True

b. False


4. Which method is not used to make bacterial cells that have new genes?

a. Conjugation

b. Cloning

c. Transformation

d. Transduction

e. Transposition


5. Which is not true of the promoter region?

a. The promoter region is a segment of DNA.

b. The promoter region is where RNA polymerase binds in prokaryotes to begin

transcription.

c. All RNA polymerases bind equally well to all promoters.

d. The promoter region is near to or overlaps the operator region.

e. The promoter region is the site for lac repressor binding.


6. Which sequences of DNA encode a diffusible product?

a. lac O

b. lac I

c. lac Z

d. Both a and b

e. Both b and c


7. Which of the following is not one of the ways in which an animal virus can enter the

cell?

a. The membrane of the host and the enveloped virus fuse, releasing the rest of the virion

into the cell.

b. A naked virion is taken up by endocytosis.

c. The viral membrane is studded with glycoproteins that bind to the host cell’s plasma

membrane.

d. The host cell digests the protein capsid, liberating the viral nucleic acid, which takes

charge of the host cell.

e. The virus must pass through a cell wall as well as a plasma membrane.


8. In the regulation of genes for lactose metabolism, lactose functions as

a. an inducer.

b. the substrate of the enzyme encoded by a structural gene.

c. an inducible enzyme.

d. Both a and b

e. Both b and c


9. Which of the following statements about plasmids is true?

a. Plasmids are viruses.

b. In plasmids, R factors encode the genes needed for conjugation.

c. Plasmids are tiny bacteria.

d. In plasmids, F factors may confer resistance to antibiotics.

e. Plasmids can move between cells during conjugation.


10. A repressor

a. slows down the mRNA process when it is attached to an operator.

b. always consists of a promoter, an operator and two or more structural genes.

c. blocks the transcription of mRNA when it is not bound to the operator.

d. bound to an operator, blocks transcription of the structural gene.

e. has three binding sites.


11. In the _______ of lactose, the lac _______ binds to the lac _______ site.

a. presence; operator; repressor

b. presence; repressor; promoter

c. absence; operator; promoter

d. absence; operator; repressor

e. absence; repressor; operator


12. The CRP-cAMP system

a. can be found operating when preferred energy sources are abundant.

b. increases the efficiency of promoters.

c. elevates the level of transcription of structural genes.

d. functions to limit the activity of a promoter.

e. normally binds just downstream (5’) from the promoter.


13. The promoter is

a. the region that binds RNA polymerase.

b. the region that binds the operator.

c. functionally equivalent to the repressor.

d. a gene that encodes for tryptophan.

e. a structural gene.


14. Which statement about transposable elements is true?

a. They are large elements that carry one or more additional genes.

b. They are cut from their original sites and are inserted elsewhere through replication.

c. Their replication depends on the rest of the chromosome.

d. Their insertion often produces genotypic effects.

e. They can be inserted into a new location on the same chromosome or into another

chromosome.


15. Tryptophan is

a. an inducer of the trp operon.

b. a corepressor of the trp operon.

c. a mutation in the trp operon.

d. a gene.



16. In the lac operon,

a. the repressor binds to the operator when lac is present.

b. a corepressor unites with the repressor.

c. transcription is inhibited when the repressor binds to the operator.

d. lactose binding alters the shape of the operator.

e. the control mechanism is positive.


17. When lactose is _______ in the cell, it binds to the _______ site of the lac

_________.

a. absent; allosteric; repressor

b. present; allosteric; repressor

c. absent; active; repressor

d. present; active,; promoter

e. absent; allosteric; promoter


18. CRP is responsible for positive regulation of the lac operon because

a. CRP binds cAMP.

b. CRP binds the CRP binding site.

c. CRP prevents binding of the repressor to the operator.

d. CRP bound to the CRP binding site near the promoter increases the frequency of

transcription initiation by RNA polymerase.

e. extracellular glucose levels influence the ability of CRP to bind to the CRP binding

site.


19. The trp operon encodes genes for tryptophan biosynthesis and is regulated by

a. tryptophan, the trp repressor.

b. the concentration of glucose.

c. cell size, the trp repressor.

d. tryptophan, the trp repressor.



20. What types of information can be obtained from a genomic sequence?

a. ORF (open reading frame)

b. Amino acid sequence

c. Regulatory sequences

d. Only a and b

e. All of the above


Genomes? p. 300

TEXTBOOK END-OF-CHAPTER QUESTIONS

1. Which of the following statements about the lac operon is not true?

a. When lactose binds to the repressor, the repressor can no longer bind to the operator.

b. When lactose binds to the operator, transcription is stimulated.

c. When the repressor binds to the operator, transcription is inhibited.

d. When lactose binds to the repressor, the shape of the repressor is changed.

e. When the repressor is mutated, one possibility is that it does not bind to the operator.

2. Which of the following is not a type of viral reproduction?

a. DNA virus in a lytic cycle

b. DNA virus in a lysogenic cycle

c. RNA virus by a double-stranded RNA intermediate

d. RNA virus by reverse transcription to make cDNA

e. RNA virus by acting as tRNA

3. In the lysogenic cycle of bacteriophage ,

a. a repressor, cI, blocks the lytic cycle.

b. a bacteriophage carries DNA between bacterial cells.

c. both early and late phage genes are transcribed.

d. the viral genome is made into RNA, which stays in the host cell.

e. many new viruses are made immediately, regardless of host health.

4. An operon is

a. a molecule that can turn genes on and off.

b. an inducer bound to a repressor.

c. a series of regulatory sequences controlling transcription of protein-coding genes.

d. any long sequence of DNA.

e. a promoter, an operator, and a group of linked structural genes.

5. Which statement is true of both transformation and

transduction?

a. DNA is transferred between viruses and bacteria.

b. Neither occurs in nature.

c. Small fragments of DNA move from one cell to another.

d. Recombination between the incoming DNA and host cell DNA does not occur.

e. A conjugation tube is used to transfer DNA between cells.

6. Plasmids

a. are circular protein molecules.

b. are required by bacteria.

c. are tiny bacteria.

d. may confer resistance to antibiotics.

e. are a form of transposable element.

7. The minimal genome can be estimated for a prokaryote

a. by counting the total number of genes.

b. by comparative genomics.

c. as about 5,000 genes.

d. by transposon mutagenesis, one gene at a time.

e. by leaving out genes coding for tRNA.

8. When tryptophan accumulates in a bacterial cell,

a. it binds to the operator, preventing transcription of adjacent genes.

b. it binds to the promoter, allowing transcription of adjacent genes.

c. it binds to the repressor, causing it to bind to the operator.

d. it binds to the genes that code for enzymes.

e. it binds to RNA and initiates a negative feedback loop to reduce transcription.

9. The promoter in the lac operon is

a. the region that binds the repressor.

b. the region that binds RNA polymerase.

c. the gene that codes for the repressor.

d. a structural gene.

e. an operon.

10. The CRP–cAMP system

a. produces many catabolites.

b. requires ribosomes.

c. operates by an operator–repressor mechanism.

d. is an example of positive control of transcription.

e. relies on operators.

ANSWERS

TEST FILE

Multiple Choice

1. e

2. a

3. e

4. b

5. a

6. d

7. c

8. c

9. c

10. a

11. b

12. e

13. d

14. a

15. a

16. d

17. c

18. b

19. c

20. e

21. c

22. a

23. b

24. c

25. b

26. a

27. d

28. c

29. a

30. a

31. d

32. e

33. d

34. b

35. d

36. c

37. b

38. d

39. d

40. a

41. e

42. d

43. e

44. a

45. b

46. e

47. a

48. a

49. e

50. b

51. c

52. e

53. a

54. c

55. d

56. d

57. c

58. d

59. b

60. d

61. a

62. a

63. d

64. a

65. a

66. a

67. c

68. b

69. e

70. c

71. b

72. d

73. d

74. b

Fill in the Blank

1. tobacco mosaic

2. virion

3. virion

4. lysogenic

5. prophage

6. temperate

7. provirus

8. Plasmids

9. fertility factors (or F

factors)

10. transposable

elements (or

transposons)

11. viral

12. evolution

13. structural

14. lac

15. operons

16. promoter

17. operator

18. regulatory

19. repressible

20. catabolic repression

21. comparative

genomics

22. universal

Diagram

1. b

STUDY GUIDE

Knowledge and Synthesis

1. d. Nucleic acids do not form capsids; cell walls are found in bacterial and plant cells,

not viruses. Viruses are organized so that the nucleic acid is surrounded by protein (not

membranes), and the protein capsid may be surrounded by a membrane.

2. d. Bacteriophage must bind to cell surface receptors to initiate their infective cycle. In

bacteriophage , a prophage (a viral chromosome inserted into the host chromosome)

prevents other phage from infecting that bacterium. Bacteria that are resistant to viruses

cannot be infected by them and thus cannot be lysed.

3. c. This sequence includes the most complete details of the viral life cycle.

4. d. Answer b describes a provirus, which is a bacterial virus that has inserted its genome

into a host chromosome.

5. d. Answer a describes transduction, b describes one possible result of conjugation, and

c describes what happens during conjugation.

6. d. All of these genes can be found on plasmid molecules.

7. b. An operon is a set of genes that are all transcribed from the same promoter. Answer

a is not correct. The repressor binds at the operator site, which overlaps the promoter.

Answer d is not correct because the operon is regulated transcriptionally, not

translationally.

8. c. If the lac repressor is nonfunctional, it cannot bind the operator site, and

transcription of the lac operon will occur at all times, whether or not lactose is present.

9. a. If the repressor can no longer bind tryptophan, then it cannot bind the operator, and

transcription of the trp operon will always be on, whether tryptophan levels in the cell are

high or low.

10. d. Answer a refers to the lac and trp repressors, answer b to the CRP protein, and

answer c to promoters that have different transcriptional efficiencies.

11. a. Functional genomics assigns functions to genes, not the regulatory sequences.

Comparative genomics compares genes between different organisms to see what genes

one organism has that another is missing. These comparisons can be related to the

physiology of the organisms that are being compared.

12. c. Comparative genomics compares genes between different organisms to see what

genes one organism has that another is missing. These comparisons can be related to the

physiology of the organisms that are being compared. Functional genomics assigns

functions to genes, not the regulatory sequences.

13. b. If an essential gene in a bacterial cell is inactivated by the insertion of a transposon,

that bacterium will die.

14. d. In order for viruses to infect plant cells, they must be able to get through the cell

walls. They are transmitted most often by insects and can move from cell to cell through

cytoplasmic bridges called plasmodesmata.

15. c. The decision to become a prophage by bacteriophage is made when cI binds the

promoter. This decision is made if the host is experiencing rich nutrient conditions, and

results in lysogeny, not cell lysis.

Application

1. Animal viruses cannot express their genes, replicate their genomes, or multiply unless

they are in the cytoplasm of the host cell. They use the host cell’s components

(ribosomes, ATP) to grow and reproduce.

2. Most antibiotics attack bacterial cells by inhibiting prokaryotic translation. Animal

viruses use the host translation machinery, which is different enough from the bacterial

translation machinery that it is unaffected by antibiotics. Drugs that would inhibit host

translation would kill the host cell (by preventing protein synthesis) as well as the animal

virus.

3. The tuberculosis bacterium must use lipids as a source of energy-rich compounds;

inhibiting lipid synthesis in this bacterium may inhibit the growth of this bacterium.

4. Yes. The repressor gene can be transcribed and translated from the plasmid DNA, and

normal regulation will be restored.

5. No. The operator site on the plasmid cannot restore regulation unless it recombines

with the host operator site in such a way that it replaces the mutant operator on the host

chromosome. The DNA site on the plasmid would bind repressor, but because that site is

not adjacent to the promoter or the structural genes on the chromosome, normal

regulation of those genes cannot occur.

6. Converting an auxotroph to a prototroph would require the introduction of a wild-type

copy of the gene that was nonfunctional in the auxotroph (for example, introducing a

gene that encoded an enzyme necessary for leucine biosynthesis to a leucine auxotroph

lacking that enzyme). The wild-type copy of this gene could be introduced to the recipient

cell by conjugation, transformation, or transduction.

ONLINE QUIZ

1. d

2. e

3. b

4. e

5. c

6. e

7. e

8. d

9. e

10. d

11. e

12. b

13. a

14. e

15. b

16. c

17. b

18. d

19. a

20. e

TEXTBOOK END-OF-CHAPTER

1. b

2. e

3. a

4. c

5. c

6. d

7. d

8. c

9. b

10. d

Health & Medicine

Ch13 test file