Microbiology Chapter 6

1. Viruses have typical cellular structure like other living organisms.

2. Viruses in the extracellular state possess few, if any, active enzymes.

3. Which is not true of viruses? A. They can exist in an intracellular or extracellular phase. B. They infect animal and plant cells only. C. They can be observed with an electron microscope. D. They are acellular. E. They replicate only inside host cells.

4. Which of the following is true of viruses in the extracellular phase? A. They possess many different enzymes. B. They can reproduce independently of living cells but only at a slow rate. C. They behave as a macromolecular complex and are no more alive than are ribosomes. D. They possess many different enzymes and they can reproduce independently of living cells but only at a slow rate.

5. A complete virus particle is called a A. capsid. B. nucleocapsid. C. virion. D. cell.

6. The nucleic acids carried by viruses usually consist of A. DNA. B. RNA. C. either DNA or RNA. D. both DNA and RNA simultaneously.

7. Which of the following is not true of viruses? A. Viruses are acellular. B. Viruses consist of one or more molecules of DNA or RNA enclosed in a coat of protein and sometimes in other more complex layers. C. Viruses can exist in two phases: intracellular and extracellular. D. Viruses replicate by binary fission.

8. Viruses infecting protists, including algae, have never been detected.

9. One way in which small viruses package more information into a very small genome is to use overlapping genes so that the same base sequence is read in more than one reading frame.

10. Almost all known plant viruses are RNA viruses.

11. Virus morphology does not include which of the following characteristics? A. Size B. Shape C. Presence or absence of an envelope D. Host range

12. __________ are glycoprotein spikes protruding from the outer surface of the viral envelope.

13. Icosahedral viruses are constructed from ring- or knob-shaped units called __________.

14. Viruses that are polyhedrons with 20 sides are said to have __________ symmetry.

15. The most common capsid morphologies are icosahedral and helical.

16. The largest of the viruses are similar in size to some small bacteria and are large enough to be seen with a light microscope.

17. The presence or absence of an envelope is not useful in classifying viruses because any given virus may at one time have an envelope and at another time not have an envelope.

18. Viruses such as MS2 and Qß pack additional information into their genomes through the use of overlapping genes.

19. The simplest viruses consist of A. RNA only. B. Protein only. C. RNA or DNA in a protein coat. D. RNA or DNA in a protein coat covered with lipid envelope. E. RNA, DNA and enzymes in a protein coat with a lipid envelope.

20. Viral capsid protein subunits are called A. auxomers. B. elastomers. C. protomers. D. viromers.

21. In an enveloped virus, the part of the virus including the nucleic acid genome and the surrounding protein coat but not the envelope is called the A. capsid. B. nucleocapsid. C. matrix. D. virion.

22. Some complex viruses have icosahedral symmetry in the head region and helical symmetry in the tail. Overall, these viruses are said to have __________ symmetry. A. bilateral B. binal C. complex D. none of these

23. Glycoprotein spikes protruding from the outer surface of viral envelopes function as A. toxins. B. factors that bind to host cells. C. cell lysis factors. D. factors needed for site specific recombination.

24. A __________ genome exists as several separate, nonidentical molecules that may be packaged together or separately. A. diploid B. segmented C. polyploid D. fractionated

25. Many of the enzymes found in virus particles are A. required for viral attachment to host cells. B. involved in viral entry into host cells. C. involved in the replication of viral nucleic acid. D. All of the choices are correct.

26. Which of the following is/are not true about viral envelopes? A. The envelope proteins are virus specific. B. The envelope lipids and carbohydrates are derived from the host. C. They are typical lipid monolayers with embedded viral proteins. D. The envelope proteins are virus specific and the envelope lipids and carbohydrates are derived from the host.

27. Viral envelopes are composed of A. proteins. B. lipids. C. carbohydrates. D. All of the choices are correct.

28. Two major types of symmetry found in viruses include A. icosahedral and radial. B. icosahedral and helical. C. helical and radial. D. radial and bilateral.

29. The function of the viral protein coat is to A. protect the viral genetic material. B. aid in the transfer of the viral genetic material between host cells. C. elicit the production of protective antibodies. D. protect the viral genetic material and aid in the transfer of the viral genetic material between host cells.

30. The protein coat surrounding the viral genome is called the A. capsule. B. capsid. C. matrix. D. envelope.

31. Which of the following is most true of a viral DNA genome? A. It uses the same four nitrogenous bases found in prokaryotic and eukaryotic DNA. B. It may have the normal bases found in prokaryotic and eukaryotic DNA, or it may have one or more unusual bases. C. It is usually composed of unusual bases unique to viruses. D. Viruses do not use DNA for their genome.

32. Virion size ranges from A. 1-40 nm. B. 10-400 nm. C. 600-1,000 nm. D. 1,000-10,000 nm.

33. Viral capsids are generally constructed without any outside aid once the subunits have been synthesized. This process is called A. facilitated assembly. B. self-assembly. C. spontaneous maturation. D. self-maturation.

34. In which of the following stages of the viral infectious cycle do enveloped viruses usually acquire their envelopes? A. Penetration B. Component biosynthesis C. Assembly D. Release

35. Most enveloped viruses use the host __________ membrane as their envelope source. A. plasma B. nuclear C. mitochondrial D. none of these

36. Poliovirus receptors are found A. in cells of all tissues. B. in spinal cord anterior horn cells only. C. in nasopharynx, gut, and spinal cord anterior horn cells. D. in gut cells only.

37. Nonenveloped viruses most often gain access to eukaryotic host cells by A. fusion with the host cell plasma membrane followed by entrance of the nucleocapsid into the cytoplasm. B. endocytosis. C. pinocytosis. D. nucleic acid injection through the plasma membrane.

38. Which of the following represent(s) the way(s) in which enveloped viruses acquire their envelopes? A. Budding through the plasma membrane. B. Budding through internal cellular membranes. C. Viral enzymes are responsible for production of the envelope. D. Some viruses bud through the plasma membrane while other bud through internal cellular membranes.

39. Virus receptors are often not distributed uniformly over the surface of host cells, but are instead concentrated in lipid rafts.

40. Enveloped viruses may enter their host cells by fusion of their envelope with the cytoplasmic membrane, thereby depositing their nucleocapsid within the cell.

41. Enveloped viruses may enter their host cells by engulfment within coated vesicles (endocytosis).

42. Some viruses cause abnormal growth of cells rather than destruction. This is called __________.

43. Human cancer causing viruses most often have a ___________ genome. A. ssDNA B. dsDNA C. ssRNA D. dsRNA

44. Adult T-cell leukemia is thought to be caused by A. herpesviruses. B. retroviruses. C. parvoviruses. D. picornaviruses.

45. Genes whose expression (or abnormal expression) causes cancer are called A. cancer genes. B. progenes. C. oncogenes. D. carcinogens.

46. Which of the following has been associated with a form of liver cancer? A. Human papilloma virus B. Hepatitis B virus C. Human T-cell lymphotropic virus D. Hepatitis A virus

47. Microscopic or macroscopic degenerative changes or abnormalities in infected host cells and tissues are called __________ __________.

48. In a plaque assay, the number of infectious virions is usually identical to the number of virus particles present.

49. Animal viruses have been cultivated in A. suitable host animals. B. embryonated eggs. C. tissue cultures (monolayers of animal cells). D. All of the choices are correct.

50. Which of the following can be used to cultivate plant viruses? A. Cultures of separated plant cells B. Whole plants C. Plant protoplast cultures D. All of the choices are correct.

51. 0.2 mls of a 10-4 dilution of a virus preparation yields 90 plaques. What is the number of PFU per ml in the undiluted virus preparation? A. 9.0 × 105 B. 4.5 × 106 C. 4.5 × 107 D. 9.0 × 108

52. A ________ assay is most useful for determining the viability of a viral preparation. A. direct (electron microscopic) count B. hemagglutination C. plaque D. PCR

53. Hemagglutination is A. the clumping together of red blood cells in the presence of a viral suspension. B. the binding of iron in the process of a viral suspension. C. the clumping together of infected cells in the presence of a viral suspension. D. None of the choices are correct.

54. Like bacteria and eukaryotic microorganisms, most viruses can be cultured using artificial media.

55. Bacterial viruses are so named because they have prokaryotic cell structures similar to their bacterial hosts.

56. Localized areas of destruction occurring on plants that have been infected by a virus are referred to as __________ lesions.

57. Which of the following is not a mechanism by which viruses cause cancer? A. They carry a cancer-causing gene into the cell. B. They encode proteins that bind to and inactivate host cell proteins known as tumor suppressor proteins. C. They produce defective interfering particles. D. An expression of viral proteins results in abnormal expression of genes that regulate cell growth and reproduction.

58. Which of the following is not true of viroids? A. Viroids are small circular ssRNA molecules. B. Viroids have no protein capsids. C. Viroid RNA does not serve as mRNA nor does it direct the synthesis of mRNA. D. Extracellular viroids have a lipid bilayer envelope.

59. Viroids are of economic significance because they cause disease in A. plants. B. animals. C. humans. D. All of the choices are correct.

60. Viroids are: A. proteins that may infect man and other animals causing spongiform encephalopathy. B. a class of so-called slow viruses. C. a new class of small single stranded DNA viruses that infect some animals. D. short infectious single stranded RNAs that can infect some plants.

61. Prions are of significance because they cause infections of A. domestic animals and humans. B. plants. C. fungi. D. prokaryotes.

62. Which of the following diseases is (are) caused by prions? A. Scrapie B. Mad cow disease C. Kuru and Creutzfeldt-Jakob Disease D. All of the choices are correct.

63. Prions consist of proteins and have no apparent nucleic acid genome.

64. Available evidence is consistent with the proposal that prion diseases are caused by infectious proteins.

65. The mechanism of pathogenesis by prions may involve a conformational change in the prion protein (PrP) to an abnormal form.

66. There are no known human diseases that have been linked to prions.

67. Which virion release process is most often used by enveloped viruses? A. Lysis B. Facilitated diffusion C. Budding D. Diffusion through channel protein

68. Which type of virus is most likely to be released by lysis of the host cell? A. Enveloped virus B. Non-enveloped virus

69. A temperate phage always lyses its host cell.

70. For a temperate phage to produce more phage, which of the following must happen? A. Lysogeny B. Induction C. Lysogenic conversion D. Prophage formation

71. The production of cholera toxin by virulent strains of Vibrio cholera is dependent upon genes in a bacteriophage. This is an example of A. lysogenic conversion. B. induction. C. bacterial transformation. D. transduction.

72. Diphtheria toxin is produced only by strains of Corynebacterium diphtheriae that are infected with a particular bacteriophage. This is an example of A. conjugation. B. induction. C. lysis. D. lysogenic conversion.

73. Which type of phage always lyses its host cell? A. Temperate B. Virulent C. Lysogenic D. Prophage

74. Place the following steps in the correct order to reflect how a plaque assay is done: Plates from different dilutions are examined and plaques are counted. Dilutions are mixed with the appropriate bacterial host. Bacterial/sample dilution mixtures are plated on agar plates. Several dilutions of sample to be assayed are prepared. Plates are incubated to allow for plaque development.

75. Laboratory animals must be used to determine lethal and infectious doses of viruses.

76. Place the steps in the correct order to reflect how a lethal dose may be determined. 1 Dilutions of virus are made to represent a range of concentrations. 3 Inoculated host cells are observed and the number of dead cells are counted. 4 The dilution which killed 50% of the tissue culture cells is identified. 2 Dilutions are inoculated into susceptible tissue cultures (or susceptible host organisms).

77. Which of the following encodes its own capsid proteins? A. Satellite virus B. Satellite DNA C. Satellite RNA D. Prion

78. Which of the following is/are necessary for the replication of a satellite virus? A. Host cell only B. Helper virus only C. Prion only D. Host cell and helper virus

79. The most notable difference between PrPC (normal protein) and PrPSc (prion protein) is A. PrPC is a much longer polypeptide chain, compared to PrPSc. B. PrPC causes a cell to undergo rapid apoptosis. C. PrPc folds appropriately whereas PrPSc does not fold correctly. D. PrPc is a functional glycolytic enzymewhereas PrPSc is nonfunctional.

80. All of the following are methods of prion disease transmission EXCEPT A. ingestion of infected tissue. B. inheritance (genetic). C. organ or tissue transplantation. D. contamination through use of inadequately processed surgical instruments. E. inhalation (airborne).

81. A PrPc protein can convert a PrPSc to a PrPc.

82. What is the minimum number of phage that can initiate the development of a plaque in a bacterial lawn? A. 1 B. 5 C. 10 D. 25

83. Creutzfeldt-Jacob disease is known to have been transmitted by surgical instruments and transplanted nerve tissue.