Chapter 18: The Genetics of Viruses and Bacteria
30) Reproduction in bacteria requires A) the production of a mitotic spindle. B) a plasmid. C) cyclic AMP. D) replication of DNA. E) both B and D
D
58) Of the following, which is least related to the others? A) corepressor B) repressor C) inducer D) transposon E) cAMP receptor protein
D
1) Which of the following is (are) true about viruses? A) Viruses are classified below the cellular level of biological organization. B) A single virus particle contains both DNA and RNA. C) Even small virus particles are visible with light microscopes. D) Only A and B are true. E) A, B, and C are true.
A
18) Which of the following is a true statement? A) Viruses are uncommon. B) Viruses can cause diarrhea, colds, and measles. C) All viruses have a similar capsid and membranous envelope. D) All viruses contain the nucleic acid RNA. E) Viruses only invade animal cells.
B
20) RNA viruses appear to have higher rates of mutation because A) RNA nucleotides are more unstable than DNA nucleotides. B) replication of their genomes does not involve the proofreading steps of DNA replication. C) RNA viruses replicate faster. D) RNA viruses can incorporate a variety of nonstandard bases. E) RNA viruses are more sensitive to mutagens
B
25) Which of the following is true of plant virus infections? A) They can be controlled by the use of antibiotics. B) They are spread throughout a plant by passing through the plasmodesmata. C) They have little effect on plant growth. D) Only A and B are correct. E) A, B, and C are correct.
B
11) Virulent phages undergo a(n) ________ life cycle, whereas temperate phages are capable of undergoing a(n) ________ cycle. A) infective; retroviral B) lysogenic; lytic C) lytic; lysogenic D) retroviral; infective E) infective; benign
C
17) The simplest infectious biological systems are A) bacteria. B) viruses. C) viroids. D) both A and B E) both B and C
C
22) If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities? A) I B) II C) III D) IV E) either II or IV
C
A. operon B. inducer C. promoter D. repressor E. corepressor 50) A lack of this nonprotein molecule would result in the inability of the cell to "turn off" genes.
E
14) What is the function of reverse transcriptase in retroviruses? A) It hydrolyzes the host cell's DNA. B) It uses viral RNA as a template for DNA synthesis. C) It converts host cell RNA into viral DNA. D) It translates viral RNA into proteins. E) It uses viral RNA as a template for making complementary RNA strands.
B
46) The role of a metabolite that controls a repressible operon is to A) bind to the promoter region and decrease the affinity of RNA polymerase for the promoter. B) bind to the operator region and block the attachment of RNA polymerase to the promoter. C) increase the production of inactive repressor proteins. D) bind to the repressor protein and inactivate it. E) bind to the repressor protein and activate it.
E
10) Which of the following statements about the lysogenic cycle of lambda (λ) phage is incorrect? A) After infection the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. B) Most of the prophage genes are silenced by the product of a particular prophage gene. C) The phage genome replicates along with the host genome. D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lysogenic to the lytic cycle. E) The phage DNA is incorporated by genetic recombination (crossing over) into a specific site on the host cell's DNA.
A
13) Viruses with single-stranded RNA that acts as a template for DNA synthesis are known as A) retroviruses. B) proviruses. C) viroids. D) bacteriophages. E) lytic phages.
A
16) Viral envelopes contain proteins with covalently attached carbohydrate groups called A) glycoproteins. B) proteosugars. C) carbopeptides. D) peptidocarbs. E) carboproteins.
A
27) The difference between vertical and horizontal transmission of plant viruses is that A) vertical transmission refers to the transmission of a virus from a parent plant to its progeny, and horizontal transmission refers to one plant spreading the virus to another plant. B) vertical transmission refers to the spread of viruses from upper leaves to lower leaves of the plant, and horizontal transmission refers to the spread of a virus among leaves at the same general level. C) vertical transmission refers to the spread of viruses from trees and tall plants to bushes and other smaller plants, and horizontal transmission refers to the spread of viruses among plants of similar size. D) vertical transmission refers to the transfer of DNA from one type of plant virus to another, and horizontal transmission refers to the exchange of DNA between two plant viruses of the same type. E) vertical transmission refers to the transfer of DNA from a plant of one species to a plant of a different species, and horizontal transmission refers to the spread of viruses among plants of the same species.
A
28) What are prions? A) misfolded versions of normal brain protein B) tiny molecules of RNA that infect plants C) viral DNA that has had to attach itself to the host genome D) viruses that invade bacteria E) a mobile segment of DNA
A
37) In biotechnology, genes are commonly introduced into bacterial cells by incubating the cells together with DNA and high concentrations of calcium ions. This is an example of A) transformation. B) translocation. C) transduction. D) conjugation. E) transposition.
A
42) Which of the following statements regarding transposons is not true? A) Transposons are genes that encode sex pili and enable plasmid transfers between bacteria. B) Transposons are found in both prokaryotes and eukaryotes. C) Transposons can move from a plasmid to the bacterial circular chromosome. D) Transposons may replicate at an original site and insert a copy at another site. E) Transposons may carry only the genes necessary for insertion.
A
43) An R plasmid can A) facilitate bacterial resistance to antibiotics. B) adjust the rates of metabolic pathways. C) repress gene expression. D) convert an F+ to an F- bacterium. E) reverse the direction of transcription.
A
44) What does the operon model attempt to explain? A) the coordinated control of gene expression in bacteria B) bacterial resistance to antibiotics C) how genes move between homologous regions of DNA D) the mechanism of viral attachment to a host cell E) horizontal transmission of plant viruses
A
45) All of the following are made up of nucleic acid except a A) repressor. B) structural gene. C) promoter. D) regulatory gene. E) operator.
A
51) A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in A) continuous transcription of the structural gene controlled by that regulator. B) complete inhibition of transcription of the structural gene controlled by that regulator. C) irreversible binding of the repressor to the operator. D) inactivation of RNA polymerase. E) both B and C
A
54) Which of the following statements about operons is (are) true? A) The tryptophan operon is a repressible operon. B) Tryptophan itself can bind to the trp operator and shut down production of tryptophan pathway enzymes. C) The lactose operon repressor binds to the operator and turns on the synthesis of the enzyme β-galactosidase. D) Only A and C are correct. E) A, B, and C are correct.
A
7) Viruses are referred to as obligate parasites because A) they cannot reproduce outside of a host cell. B) viral DNA always inserts itself into host DNA. C) they invariably kill any cell they infect. D) they can incorporate nucleic acids from other viruses. E) they must use enzymes encoded by the virus itself.
A
A. transduction B. transposition C. translation D. transformation E. conjugation 33) DNA is transferred from one bacterium to another by a virus
A
You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements smaller than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious 21) Which treatment could definitively determine whether or not the component is a viroid? A) I B) II C) III D) IV E) first II and then III
A
26) Which of the following represents a difference between viruses and viroids? A) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells. B) Viruses have capsids composed of protein, whereas viroids have no capsids. C) Viruses contain introns; viroids have only exons. D) Viruses always have genomes composed of DNA, whereas viroids always have genomes composed of RNA. E) Viruses cannot pass through plasmodesmata; viroids can.
B
40) What does bacterial mating involve? A) exchange of egg and sperm B) formation of a cytoplasmic bridge for the transfer of "male" DNA C) sex pili that draw the cells together so that mRNA can be inserted D) integration of male and female DNA into a cytoplasmic bridge E) binary fission of a bacterial cell
B
53) Transcription of the structural genes in an inducible operon A) occurs all the time. B) starts when the pathway's substrate is present. C) starts when the pathway's product is present. D) stops when the pathway's product is present. E) does not produce enzymes.
B
57) Allolactose induces the synthesis of the enzyme lactase. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when the lactose enters the cell? A) The repressor protein attaches to the regulator. B) Allolactose binds to the repressor protein. C) Allolactose binds to the regulator. D) The repressor protein and allolactose bind to RNA polymerase. E) RNA polymerase attaches to the regulator.
B
A. transduction B. transposition C. translation D. transformation E. conjugation 36) A sequence of DNA is moved to alternative locations within the genome.
B
3) A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur? A) The plants would develop some but not all of the symptoms of the TMV infection. B) The plants would develop symptoms typically produced by viroids. C) The plants would develop the typical symptoms of TMV infection. D) The plants would not show any disease symptoms. E) The plants would become infected, but the sap from these plants would be unable to infect other plants.
C
39) A scientist is studying a strain of bacteria that commonly transfers genes to other bacteria. Which of the following would provide evidence that the genes are being transferred through specialized transduction? A) Transmission of the genes is always accompanied by transfer of the F plasmid. B) Transmission of the genes is always accompanied by transfer of the R plasmid. C) The same one or several gene(s) are always transferred. D) The transmission of the genes is dramatically enhanced in the presence of calcium. E) The bacterial strain is often infected by a virulent phage.
C
56) For a repressible operon to be transcribed, which of the following must be true? A) A corepressor must be present. B) RNA polymerase and the active repressor must be present. C) RNA polymerase must bind to the promoter, and the repressor must be inactive. D) RNA polymerase cannot be present, and the repressor must be inactive. E) RNA polymerase must not occupy the promoter, and the repressor must be inactive
C
9) Bacteriophage DNA that have become integrated into the host cell chromosome are called A) intemperate bacteriophages. B) transposons. C) prophages. D) T-even phages. E) plasmids.
C
A. operon B. inducer C. promoter D. repressor E. corepressor 49) A mutation in this section of DNA could influence the binding of RNA polymerase to the DNA.
C
19) Which of the following can be effective against viral diseases? A) vaccination B) nucleoside analogs that inhibit DNA synthesis C) antibiotics D) A and B only E) A, B, and C
D
2) Which of the following is not a reason scientists suspected that something other than bacteria was the cause of tobacco mosaic disease? A) Passing infectious sap through a fine filter failed to remove the infectious agent. B) Treating infectious sap with alcohol failed to remove the infectious agent. C) No cells could be seen in the infectious sap using a light microscope. D) The infectious agent in the sap could reproduce, as its ability to cause disease was undiluted even after many transfers from plant to plant. E) The infectious agent could not be cultivated on nutrient media in petri dishes or in test tubes.
D
23) Which treatment would you use to determine if the agent is a prion? A) I only B) II only C) III only D) IV only E) either I or IV
D
24) Which of the following contributes to the emergence of viral disease? A) production of new virus strains through mutation B) spread of existing virus from one host species to another C) transformation from lytic to lysogenic activity D) A and B only E) A, B, and C
D
38) The process by which host cell DNA is accidentally packaged within a phage capsid and transferred to another cell instead of the phage DNA is called A) translocation. B) conjugation. C) specialized transduction. D) generalized transduction. E) transformation.
D
4) Which of the following is a characteristic of all viruses? A) a nucleic acid genome B) a protein capsid C) a viral envelope D) A and B only E) A, B, and C
D
55) How does active CAP induce expression of the genes of the lactose operon? A) It terminates production of repressor molecules. B) It degrades the substrate allolactose. C) It stimulates splicing of the encoded genes. D) It stimulates the binding of RNA polymerase to the promoter. E) It binds steroid hormones and controls translation
D
8) Which of the following is characteristic of the lytic cycle? A) Many bacterial cells containing viral DNA are produced. B) Viral DNA is incorporated into the host genome. C) The viral genome replicates without destroying the host. D) A large number of phages are released at a time. E) The virus-host relationship usually lasts for generations.
D
A. operon B. inducer C. promoter D. repressor E. corepressor 48) This protein is produced by a regulatory gene.
D
A. transduction B. transposition C. translation D. transformation E. conjugation 32) External DNA is assimilated by a cell.
D
12) What is the function of the single-stranded RNA in certain animal viruses? A) It can serve directly as mRNA. B) It can serve as a template for mRNA synthesis. C) It can serve as a template for DNA synthesis. D) Only A and C are correct. E) A, B, and C are correct.
E
15) The membrane making up the viral envelope can come from A) the virus itself, using enzymes encoded by the virus. B) the nuclear membrane of an infected cell. C) the plasma membrane of an infected cell. D) both A and B E) both B and C
E
29) Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory? A) Viruses contain either DNA or RNA. B) Viruses are enclosed in protein capsids rather than plasma membranes. C) Viruses can reproduce only inside host cells. D) Viruses can infect both prokaryotic and eukaryotic cells. E) Viral genomes are usually more similar to the genome of the host cell than to the genomes of viruses that infect other cell types.
E
31) What is the most common source of genetic diversity in a bacterial colony? A) transposons B) plasmids C) meiotic recombination D) crossing over E) mutation
E
41) An Hfr bacterium is one that has A) at least one plasmid present in the cytosol. B) a special recognition site that will take up closely related DNA from its environment. C) several insertion sequences scattered throughout its chromosome. D) several copies of a single transposon repeated randomly throughout its chromosome. E) a plasmid that has become integrated into its chromosome.
E
47) The tryptophan operon is a repressible operon that is A) permanently turned on. B) turned on only when tryptophan is present in the growth medium. C) turned off only when glucose is present in the growth medium. D) turned on only when glucose is present in the growth medium. E) turned off whenever tryptophan is added to the growth medium.
E
5) Viral genomes can consist of any of the following except A) double-stranded DNA. B) double-stranded RNA. C) single-stranded DNA. D) single-stranded RNA. E) helical capsomeres.
E
52) The lactose operon is likely to be transcribed when A) there is more glucose in the cell than lactose. B) the cyclic AMP levels are low. C) there is lactose but no glucose in the cell. D) the cyclic AMP and lactose levels are both high within the cell. E) both C and D
E
6) The host range of a virus is determined by A) the proteins on its surface. B) whether its nucleic acid is DNA or RNA. C) the proteins on the surface of the host cell. D) the enzymes produced by the virus before it infects the cell. E) both A and C
E
A. transduction B. transposition C. translation D. transformation E. conjugation 34) A group of F+ bacteria is mixed with a group of F- bacteria. After several days, all of the bacteria are F+.
E
A. transduction B. transposition C. translation D. transformation E. conjugation 35) A plasmid is exchanged between bacteria through a pilus.
E