Microbio Chapter 13

In contrast to most dsDNA animal viruses, the pox viruses replicate solely in the cytoplasm of the host cell. What does this suggest about the virus?

All cellular DNA replication occurs in the nucleus. DNA polymerases are synthesized in the cytoplasm are transported into the nucleus where they are active. Replication of viral DNA in the cytoplasm would require DNA polymerase activity to take place in the cytoplasm. One possibility is that the viral genome includes a gene for a DNA polymerase and that a DNA polymerase enzyme is packaged in the virion. Otherwise, the virus has some mechanism for diverting cellular DNA polymerase to the cytoplasm. The first possiblity is the simpler explanation. And

22) The genome of which of the following types of animal virus can act directly as mRNA? A) retroviruses B) +ssRNA viruses C) -ssRNA viruses D) ssDNA viruses E) dsRNA viruses

B) +ssRNA viruses

38) Which of the following virus families has a double-stranded RNA genome? A) Retroviridae B) Reoviridae C) Rhadoviridae D) Orthomyxoviridae E) Filoviridae.

B) Reoviridae

17) Why is lysogeny advantageous to a bacteriophage? A) It speeds up the viral infection cycle. B) The genetic material of the bacteriophage is amplified many times over that seen in a lytic phage. C) It allows the bacteriophage to infect cells it would not normally infect. D) It allows the bacteriophage to destroy the host cell's DNA. E) It enables the bacteriophage to take over the cell.

B) The genetic material of the bacteriophage is amplified many times over that seen in a lytic phage.

1) In what ways do viruses differ from other pathogens? A) Viruses lack genetic material. B) Viruses lack cytoplasm and organelles. C) Viruses have no protein structure. D) Viruses are composed of protein only. E) Viruses are composed of both protein and lipid.

B) Viruses lack cytoplasm and organelles

11) The taxonomy of viruses includes all the following hierarchies EXCEPT A) genus. B) class. C) specific epithet. D) family. E) order.

B) class

31) Plaque assays are used for A) evaluating the cancer-causing ability of a virus. B) determining the density of phage in a culture. C) the study of prions. D) cultivating viruses that cannot be grown any other way. E) counting the number of latent phages in a cell.

B) determining the density of phage in a culture

42) Which of the following infectious particles is most susceptible to damage? A) naked capsid virus B) enveloped virus C) prions D) bacteriophage E) both naked capsid viruses and prions

B) enveloped virus

36) A lipid membrane is present in which of the following? A) naked viruses B) enveloped viruses C) prions D) viroids E) both prions and viroids

B) enveloped viruses

24) Naked capsid animal viruses are commonly released from the infected cell by ________, a process the host cell does not survive. A) budding B) lysis C) endocytosis D) membrane fusion E) exocytosis

B) lysis

26) A cell is infected with a virus carrying an oncogene sequence in its genome. What process may occur if the oncogene is expressed in the infected cell? A) lysis B) neoplasia C) lysogeny D) latency E) both lysis and neoplasia

B) neoplasia

33) Viroids infect A) bacteria. B) plants. C) fungi. D) plants and animals. E) all organisms.

B) plants

15) A(n) ________ is a bacterial virus which is integrated into the host cell DNA. A) lytic phage B) prophage C) plasmid D) transposon E) insertion phage

B) prophage

Сompare and contrast the ways in which animal, plant, and bacterial viruses gain entry into their host cells.

Because cells have different types of barriers against the outside world, viruses have evolved different ways of breaching these barriers. For example, viruses cannot easily invade cells that have rigid, protective cell walls (such as plant and bacterial cells_. Viruses that infect these cells fain entry by direct injection( as observed in bacteriophage T4), by taking advantage of damage to the cell wall (as with some plant viruses), or by enlisting the aid of insects that are themselves parasites (as with some other plant viruses). In contrast, animal cells have no cell wall; therefore, animal viruses employ three basic strategies to enter through the flexible cytoplasmic membrane. Some animal viruses directly penetrate this membrane (either the entire virus or just its genome), whereas other viruses take advantage of natural cellular processes such as phagocytosis to gain entry into the cell. Enveloped animal viruses also can use the process of membrane fusion to get inside the animal cell.

5) Host specificity of a virus is due to A) particular genes that it shares with the infected cell. B) the presence of an envelope. C) differences in size between the virus and the host cell. D) the presence or absence of a cell wall on the host cell. E) interactions between viral and cellular surface molecules.

E) interactions between viral and cellular surface molecules

30) Tumors invade other organs and tissues in a process called A) neoplasia. B) uncoating. C) latency. D) budding. E) metastasis.

E) metastasis

8) The genome of influenza virus is A) multiple pieces of linear dsDNA. B) a single circular ssRNA. C) a single linear dsRNA. D) a single circular ssDNA. E) multiple pieces of linear ssRNA.

E) multiple pieces of linear ssRNA

13) Which of the following is associated with the attachment of a bacteriophage to a bacterial cell? A) random collisions B) chemical attractions C) receptor specificity D) both chemical attractions and receptor specificity E) random collisions, chemical attractions, and receptor specificity

E) random collisions, chemical attractions, and receptor specificity

25) Which of the following membranes can give rise to a viral envelope? A) the nuclear membrane B) the cytoplasmic membrane C) the endoplasmic reticulum D) the nuclear and cytoplasmic membranes E) the nuclear and cytoplasmic membranes and the endoplasmic reticulum

E) the nuclear and cytoplasmic membranes and the endoplasmic reticulum

1) Viruses cause most human cancers.

False

6) All DNA viruses of animals replicate in the nucleus of the host cell.

False

7) Bacteriophage release is a gradual process in which small numbers are released at a time.

False

9) All viruses use the host cell's nucleic acid polymerases for replication.

False

15) In contrast with its host cells, a virus may have a (dsDNA/dsRNA/protein) genome.

dsRNA

12) Which of the following lists stages of a lytic replication cycle in order, from earliest to latest stages? I. Synthesis II. Assembly III. Attachment IV. Release V. Entry A) III, V, I, II, IV B) III, II, V, I, IV C) V, III, II, IV, I D) I, III, V, II, IV E) I, II, III, V, IV

A) III, V, I, II, IV

27) How is the HIV provirus different from a lambda-phage prophage? A) The HIV provirus is integrated permanently into the host cell's DNA. B) All subsequent generations of HIV-infected cells carry the provirus. C) All the offspring of a cell infected with a prophage will contain the virus. D) The HIV provirus is inactive inside the host cell. E) Lambda phage-infected cells produce virus slowly over time.

A) The HIV provirus is integrated permanently into the host cells DNA

43) An acute viral disease is the likely result of ________ infection. A) a lytic B) a latent C) a persistent D) a lysogenic E) either latent or lysogenic

A) a lytic

19) Replication of most ________ viruses is similar to normal cellular processes. A) dsDNA B) ssDNA C) +ssRNA D) -ssRNA E) dsRNA

A) dsDNA

39) Which of the following is a feature shared by viruses and living organisms? A) possession of a genome that directs synthesis of materials necessary for replication B) presence of cytoplasm C) metabolic capability D) responsiveness E) the ability to increase in size

A) possession of a genome that directs synthesis of material new for replication

4) Which of the following is a characteristic by which viruses are classified? A) type of nucleic acid B) type of life cycle C) number of chromosomes D) type of host E) size

A) type of nucleic acid

23) Which of the following types of animal virus requires RNA-dependent RNA transcriptase to be replicated? A) +ssRNA viruses B) ssDNA viruses C) -ssRNA viruses D) retroviruses E) dsDNA viruses

C) -ssRNA viruses

29) One mechanism by which viruses may cause cancer is to interrupt the genetic regulatory sequences of repressor proteins. Which of the following types of viruses is most likely to be involved in causing cancer by this mechanism? A) +ssRNA viruses B) dsRNA viruses C) -ssRNA viruses D) retroviruses E) both +ssRNA and -ssRNA viruses

D) retroviruses

6) Which of the following is primarily responsible for the shape of a virion? A) the type of nucleic acid B) the number of segments of the viral genome C) the source of the envelope D) the capsid E) the specific host protein the virus targets

D) the capsid

35) Which of the following infectious particles do NOT have protein in their structure? A) bacteriophages B) prions C) animal viruses D) viroids E) both prions and viroids

D) viroids

34) How are prions different from all other known infectious agents? A) They cannot reproduce outside a cell. B) They act as slow viruses. C) They cause neurological problems. D) They can be destroyed by incineration. E) They lack nucleic acid.

E) They lack nucleic acid

45) The process known as ________ is a mechanism of release for enveloped viruses. A) lytic replication B) persistent infection C) metastasis D) latency E) budding

E) budding

28) Which of the following events may occur in a lysogenic infection but NOT a proviral infection? A) uncoating B) synthesis of viral proteins C) integration D) induction E) replication

D) induction

The acellular infectious agent in Figure 13.1 is most likely a (bacteriophage/prion/viroid).

bacteriophage

21) Reverse transcriptase is associated with which of the following? A) dsDNA viruses B) +ssRNA viruses C) -ssRNA viruses D) retroviruses E) dsRNA viruses

D) retroviruses

9) Reverse transcriptase is found in the virions of some (DNA/-ssRNA/+ssRNA) viruses.

+ssRNA

10) Which of the following statements regarding virus taxonomy is TRUE? A) Viruses are classified on the basis of the taxonomy of their host organisms. B) Virus classes are well established. C) Some virus family names are derived from the name of an important member of the family. D) The species epithet is a Latin descriptor of the virion structure. E) Virus classes are based on the domain of the host organism.

C) Some virus family names are derived from the name of an important member of the family

37) What is a virion? A) a virus genome inside a cell B) an empty capsid C) a single virus particle outside a cell D) an extracellular virus genome E) a virus genome integrated into a host cell genome

C) a single virus particle outside a cell

3) A(n) ________ is a virus that infects bacterial cells. A) virion B) prion C) bacteriophage D) nucleocapsid E) envelope

C) bacteriophage

16) Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but NOT in the lysogenic cycle? A) attachment B) entry C) digestion of host DNA D) viral protein synthesis E) both digestion of host DNA and viral proteins synthesis

C) digestion of host DNA

20) Attachment of herpesviruses results in ________, a process in which the host cell facilitates viral entry. A) direct penetration B) membrane fusion C) endocytosis D) exocytosis E) lysogeny

C) endocytosis

14) The enzyme lysozyme is critical for which of the stages of a bacteriophage T4 infection cycle? A) entry B) assembly C) entry and release D) synthesis E) attachment

C) entry and release

7) Viruses that infect ________ have no known extracellular state. A) animals B) bacteria C) fungi D) plants E) both fungi and plants

C) fungi

41) The ________ of a virion determines the type of cell it enters. A) nucleic acid B) matrix proteins C) glycoproteins D) lipid molecules E) shape

C) glycoproteins

32) Disadvantages of continuous cell cultures include A) they only grow for a limited number of generations. B) the expense of preparation. C) they may be significantly different genetically from the original source animal. D) viruses do not reliably infect them. E) they are both expensive and have a limited number of divisions.

C) they may be significantly different genetically from the original source animal

44) A ________ is a mass of neoplastic cells. A) diploid culture B) metastasis C) tumor D) gall E) plaque

C) tumor

40) Small circular RNAs called ________ are plant pathogens. A) plasmids B) viruses C) viroids D) prions E) phages

C) viroids

7) The process during viral infection known as "uncoating" involves the removal of the (capsid/envelope/matrix).

Capsid

2) Viral capsids are composed of subunits called (capsomeres/nucleocapsids/prions).

Capsomeres

A scientist discovers a new virus associates with a cancer. She is able to culture it in the laboratory and begins to analyze it. What features will help her determine the virus' classification? How does this help her understand the virus' mechanism for causing cancer?

Characterization of the nucleic acid present in the virion is a first step in deterimining the classification of the virus. If it is a large DNA virus with envelope, it may be one of the herpesviridae. DNA viruses with smaller genome sizes known to cause cancer are the papillomaviruses and polymaviruses. The hepadnaviridae have a circular DNA molecule which is partially double double stranded and partially signed stranded. Very small DNA viruses which occasionally cause cancer are the adenoviridae. The presence or absence of an envelope is also useful in eliminating possibilities. The presence of a segmented genome compromised of +singlestrand RNA and the enzyme reverse transcriptase is consistent with the virus being a member of rather retroviridae. DNA sequence determination is useful for verifying the classification to a family or genus Establishing the classification of the virus can provide clues as to the possible mechanism of causing cancer, as different virus families are involved in different processes. For example, retroviruses integrate into the host DNA and may thereby disrupt the function of a tumor repressor

9) Which of the following is CORRECT regarding the viral envelope? A) It contains only viral proteins. B) It contains only host cell proteins. C) It is composed of sterols. D) It is composed of cellular phospholipid membrane, cellular and viral proteins. E) It is composed of sterols and viral proteins only.

D) It is composed of cellular phospholipid membrane, cellular and viral proteins

18) Which of the following may result from lysogenic infection? A) The bacterium is resistant to infection with similar bacteriophage. B) The bacterium can produce large quantities of phage without lysis. C) The bacterium becomes pathogenic. D) The bacterium becomes resistant to infection and becomes pathogenic. E) The bacterium becomes resistant to infection and produces large quantities of phage.

D) The bacterium becomes resistant to infection and becomes pathogenic

2) The outermost layer of a virion fulfills which of the following functions of the virus? A) protection B) recognition C) replication D) both protection and recognition E) both recognition and replication

D) both protection and recognition

8) Uncontrolled cell division in animals is known as (metastasis/neoplasia/cancer).

Neoplasia

4) Continuous cell cultures are developed from (embryonic/haploid/neoplastic) cells.

Neoplastic

Why is the synthesis of mRNA a central issue for all viruses? How do different types of viruses achieve this goal?

One way in which a virus gains control of a cell is to direct the synthesis of new viral proteins, which include such molecules as enzymes. To do this, however, the virus must provide the cell with mRNA for the production of such proteins. Viruses can achieve this goal in one of three basic ways: (1) they can import mRNA into the cell in the form of the viral genome; (2) they can allow the cell to make viral mRNA through normal cellular genetic processes by providing the cell with viral DNA; or (3) they can use unique mechanisms to convert their genomes into a form suitable for protein production. An example of the second type is the DNA virus, either ds or ss, which can take advantage of normal cellular processes to produce mRNA. An example of the third type is the -ssRNA virus, which uses a novel enzyme called RNA-dependent RNA transcriptase to convert it's genome into +ssRNA, which can then be used for protein synthesis as the in the first example. An example of the first type of virus is the +ssRNA virus; this type of genome essentially mimics the mRNA found in teh cell.

13) Nine (orders/families/classes) represent the highest level of taxonomic rank used in classifying viruses.

Orders

12) A (colony/plaque/prophage) is a clear zone on a bacterial lawn where cells have been killed by the activity of a bacteriophage.

Plaque

14) Prions are composed of a single protein called (plaque/BSE/PrP).

PrP

11) Genes that play a role in proper cell division but may also play a role in some types of cancer are called (oncogenes/proto-oncogenes/promoters).

Proto-oncogenes

3) Viruses with -ssRNA require the activity of (DNA polymerase/reverse transcriptase/RNA- dependent RNA polymerase) for their replication.

RNA-dependent RNA polymerase

10) The stage of virus infection called (assembly/entry/synthesis) is the stage most dependent on host cell proteins.

Synthesis

6) Another term for a lysogenic phage is a (temperate/latent/prophage) phage.

Temperate

Describe the mechanism by which PrP is infectious

The clue to why PrP acts as an infectious agent was found when it was discovered that all mammals contain the gene for PrP. However, under normal conditions, the protein produced from this gene, cellular PrP, is not a pathogenic agent. It is when PrP folds into an abnormal form called prion PrP that it is infectious. As prion PrP, the protein is capable of inducing copies of cellular PrP to refold into prion PrP, thereby causing the disease form of the protein to accumulate. Because the genetic information to create this protein is found in the host organism, prions are the only known example of a totally protein-based infectious agent 9

10) Fertilized chicken eggs are used to culture some vaccine strains.

True

2) Most viruses cannot be seen by light microscopy.

True

3) Protozoa are susceptible to viral attack.

True

4) Budding release of virus may result in long lasting or persistent infection.

True

5) Members of a virus family have the same type of nucleic acid.

True

8) Bovine spongiform encephalopathy is an example of a prion disease.

True

1) The extracellular state of a virus is a (capsid/nucleocapsid/virion).

Virion