Who of the following demonstrated that the causative agent of tobacco mosaic disease would pass through filters designed to retain bacteria but thought that the agent was a nonreproducing toxin?
Who of the following showed that the filterable agent that caused tobacco mosaic disease was capable of reproduction?A. JennerB. IvanowskiC. BeijerinckD. Pasteur
Who of the following devised a method for enumerating viruses that could infect bacteria?A. TwortB. d'HerelleC. both Twort and d'HerelleD. neither Twort nor d'Herelle
Who of the following separated tobacco mosaic virus particles into protein and nucleic acid?A. BawdenB. PirieC. both Bawden and PirieD. neither Bawden nor Pirie
Viruses containA. DNA.B. RNA.C. either DNA or RNA but not both simultaneously.D. both DNA and RNA simultaneously.
Animal viruses can be cultivated inA.suitable host animals.B. embryonated eggs.C. tissue cultures (monolayers of animal cells).D. All of these.
In which phase of the bacterial growth cycle is the cultivation of bacterial viruses most efficient?A. lagB. logC. stationaryD. decline
Which of the following cannot be used to cultivate plant viruses?A. cultures of separated plant cellsB. whole plantsC. plant protoplast culturesD. All of these can be used to cultivate plant viruses.
Which of the following is more sensitive to small differences in size among various viruses?A. differential centrifugationB. gradient centrifugationC. Both are sensitive to small differences in size.D. Neither is sensitive to small differences in size.
Which of the following cannot be used to denature and precipitate contaminants from viral preparations?A. heatB. pH changesC. organic solventsD. All of these can be used to denature and precipitate contaminants.
Enzymatic degradation of cellular proteins and/or nucleic acids cannot be used in the purification of viruses because the viruses are usually more sensitive to the actions of these enzymes than the contaminating host cell materials.
Which of the following is most useful in determining the viability of a viral preparation?A. a direct (electron microscopic) countB. hemagglutinationC. a plaque assayD. All are equally useful in determining the viability of a viral preparation.
Which of the following is most true of a viral DNA genome?A. It uses the same four nitrogenous bases found in procaryotic and eucaryotic DNA.B. It may have the normal bases found in procaryotic and eucaryotic 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.
The protein coat surrounding the viral genome is called theA. capsule.B. capsid.C. matrix.D. envelope.
The two major types of symmetry found in viruses areA. icosahedral and radial.B. icosahedral and helical.C. helical and radial.D. radial and bilateral.
Viral envelopes are composed ofA. proteins.B. lipids.C. carbohydrates.D. All of these.
Which of the following is true about viral envelopes?A. The envelope proteins are virus specific.B. The envelope lipids and carbohydrates are derived from the host.C. Both of these answers are true.D. Neither of these answers is true.
Viruses are subgrouped according toA. nucleic acid type (DNA or RNA).B. nucleic acid strandedness (single or double).C. presence or absence of an envelope.D. All of these.
Who of the following instituted vaccination procedures as a preventive measure against smallpox?A. PasteurB. JennerC. ListerD. Lwoff
A complete virus particle is called aA. capsid.B. nucleocapsid.C. virion.D. cell.
Which of the following is not true about the word Virus?A. It is of Latin origin meaning poison.B. It was used to describe disease-causing agents long before such agents were observed.C. It is currently used to describe small acellular entities that cause disease.D. All of these are true about the word Virus.
Centrifugation of a suspension at various speeds in order to separate particles of various sizes is called __________ centrifugation.A. isopycnicB. densityC. differentialD. variable
In gradient density centrifugation, which of the following is true?A. Particles will continue to settle toward the bottom of the tube for as long as the centrifugation is continued.B. Particles will come to rest when the density of the surrounding medium is equal to the density of the particle even if the centrifugation is continued longer.C. The smallest particle will sediment fastest.D. Large particles will sediment farther than small particles.
A __________ genome exists as several separate, nonidentical molecules that may be packaged together or separately.A. diploidB. segmentedC. polyploidD. fractionated
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.C. Both of these answers are true.D. Neither of these answers is true.
Glycoprotein spikes protruding from the outer surface of viral envelopes may be involved inA. viral recognition of host cells.B. viral attachment to host cells.C. both viral recognition of and viral attachment to host cells.D. neither viral recognition of nor viral attachment to host cells.
In a plaque assay, each viral plaque is assumed to have arisen from the reproduction of __________ virion(s).A. oneB. twoC. one or moreD. more than one
In a plaque assay, the number of infectious virions is usually __________ the number of virus particles present.A. equal toB. less thanC. greater thanD. not predictable relative to
Who of the following demonstrated that leukemia in chickens was caused by a filterable agent?A. EllermanB. BangC. both Ellerman and BangD. neither Ellerman nor Bang
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 theA. capsid.B. nucleocapsid.C. matrix.D. virion.
Hemagglutination isA. 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 these.
Who showed that hoof and mouth disease was caused by a filterable virus?A. Loeffler and FroschB. Ellerman and BangC. Bawden and PirieD. None of these.
Viral capsid protein subunits are calledA. auxomers.B. elastomers.C. protomers.D. viromers.
Like bacteria and eucaryotic microorganisms, viruses can be cultured on artificial media.
All capsids, regardless of the type of symmetry, tend to be rigid.
Viruses in the extracellular state possess few, if any, active enzymes.
Viruses have typical cellular structure like other living organisms.
Bacterial viruses are so named because they have the same procaryotic cell structure as their bacterial hosts.
The primary categorization of viruses is on the basis of host preference.
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.
In viral classification, greatest weight is given to the intracellular location of viral replication.
Viruses that infect bacteria were first discovered by __________ but he did not follow up on the discovery.
Tobacco mosaic virus was crystallized by __________ and shown to be mostly protein.
Viruses that are polyhedrons with 20.sides are said to have __________ symmetry.
Icosahedral viruses are constructed from ring- or knob-shaped units called __________.
__________ are glycoprotein spikes protruding from the outer surface of the viral envelope. The culture of cells in a plaque assay is usually overlayed with __________ in order to limit the spread of the virus so that only the cells immediately adjacent to the infected cells will be infected by the newly produced virions, thereby forming localized areas of cellular destruction (plaques).
__________ demonstrated that the causative agent of yellow fever in humans was filterable and could be transmitted by mosquitoes.
Microscopic or macroscopic degenerative changes or abnormalities in infected host cells and tissues are called __________.
Localized areas of destruction occurring on plants that have been infected by a virus are referred to as __________ lesions.
Which of the following are usually sensitive to ether treatment?A. enveloped virusesB. nonenveloped virusesC. both enveloped and nonenveloped virusesD. neither enveloped nor nonenveloped viruses
Viruses have been somewhat difficult to study because they cannot be cultured on artificial media.
The most important criterion (a) for the classification of bacteriophages is (are)A. phage morphology.B. nucleic acid properties.C. both phage morphology and nucleic acid properties.D. neither phage morphology nor nucleic acid properties.
On bacteriophages with tails, the tails areA. contractile.B. noncontractile.C. either contractile or noncontractile.D. There are no bacteriophages with tails.
Which of the following is true of the one-step growth experiment?A. Reproduction is synchronized.B. After infection, bacteria are diluted so that released phages will not find new cells to infect.C. Both of these answers are true.D. Neither of these answers is true.
During the one-step growth experiment, the __________ represents the shortest time required for viral reproduction.A. eclipse phaseB. latent periodC. rise periodD. maturity phase
Host enzymes that protect the host from infection by degradation of DNA from infecting bacteriophages are calledA. protection endonucleases.B. protection exonucleases.C. restriction endonucleases.D. restriction exonucleases.
Assembly of new virions proceedsA. sequentially.B. by subassemblies.C. either sequentially or by subassemblies (varies according to the host).D. either sequentially or by subassemblies (varies according to the virus).
Bacteriophages package DNA byA. building the capsid around the DNA.B. inserting the DNA into preformed, complete capsid structures.C. inserting the DNA into preformed, but incomplete capsid structures.D. either building the capsid around the DNA or inserting the DNA into preformed, but incomplete capsid structures, but not by inserting the DNA into preformed, complete capsid structures.
In order for bacteriophages to be released from the host by a lysis mechanism, enzymes are required thatA. damage the cytoplasmic membrane.B. damage the cell wall.C. damage both the cytoplasmic membrane and the cell wall.D. damage neither the cytoplasmic membrane nor the cell wall.
Which of the following is not usually true about RNA bacteriophages?A. The genome RNA is plus-stranded and can act as mRNA.B. The genome RNA is converted to double-stranded RNA before replication.C. The RNA replicase enzyme is one of the capsid proteins and enters the host cell with the genome RNA.D. All of these are usually true about RNA bacteriophages.
Establishment of lysogeny by a temperate phage is usually determined byA. the previous host infected by the virus.B. the genetic composition of the host.C. the conditions at the time of infection.D. None of these.
Entry of a virus into the lytic cycle after lysogeny has been established is calledA. lysogenic conversion.B. lysogenic reversion.C. induction.D. None of these.
In a one-step growth experiment, the early period in which no infective virions are found even inside the infected host cells is called the __________ period.A. latentB. eclipseC. riseD. plateau
The latent form of a bacteriophage genome that exists when a phage establishes lysogeny is called a:A. lysogen.B. prophage.C. viroid.D. prion.
The sequence of genes in each T4 virus within a population is the same but starts with a different gene at the 5' end. If each of these linear pieces is coiled into a circle, the gene sequences would be identical. The T4 DNA, therefore, is described as beingA. a linear circle.B. linearly permuted.C. circularly permuted.D. linearly circular.
Which of the following is not a function of the replicative form (dsDNA) of the ssDNA phage phiX174?A. direct the synthesis of more RF copiesB. direct the synthesis of minus-stranded DNAC. direct the synthesis of plus-stranded DNAD. direct the synthesis of mRNA
An enzyme that cleaves DNA at specific points, thereby destroying it, is called aA. DNA cleavase.B. terminal endonuclease.C. restriction endonuclease.D. DNA ligase.
In a one-step growth experiment, the time during which there is a rapid lysis of host cells and a release of infective virions is called the __________ period.A. latentB. eclipseC. plateauD. rise
Which of the following morphologies are not found with a bacteriophage?A. tailless phage with icosahedral symmetryB. tailed phage with binal symmetryC. filamentous phage with helical symmetryD. All of these are found in a bacteriophage.
Which of the following is not normally used as genomic nucleic acid for bacteriophages?A. -ssRNAB. dsRNAC. +ssRNAD. ssDNA
For bacteriophages with +ssRNA as their genome, which of the following is normally used as the template for the production of more genomic RNA?A. -ssRNAB. dsRNAC. -ssDNAD. dsDNA
Bacteriophages that are capable only of lytic infection, not lysogeny, are called __________ phages.A. temperateB. virulentC. intemperateD. lytigate
For most bacteriophages the synthesis of host __________ is halted.A. DNAB. RNAC. proteinD. All of these.
Which of the following is (are) needed for the release of lytic phages?A. enzymes that damage the cytoplasmic membraneB. enzymes that damage the cell wallC. both enzymes that damage the cytoplasmic membrane and enzymes that damage the cell wallD. neither enzymes that damage the cytoplasmic membrane nor enzymes that damage the cell wall
Generally, a __________ multiplicity of infection (MOI) will favor lysogeny.A. lowB. highC. mediumD. Lysogeny is always favored regardless of MOI.
Early mRNA is synthesized before __________, whereas any RNA synthesized after that time is called late mRNA.
__________ is an unusual base found in the DNA of T-even phages.
A __________ is a base sequence repeated at both ends of a DNA molecule.
Early viral mRNAs are usually transcribed by a virus specific polymerase that is carried in the free virion.
Lysogeny requires integration of the viral genome into the host chromosome.
In the one-step growth experiment reproduction of the virus is synchronized.
In the one-step growth experiment the bacteria are diluted after infection so that newly released viruses will be unable to find new cells to infect.
In viral infections all of the viral genes are usually expressed prior to the replication of viral nucleic acid.
Some bacteriophages are released without lysing the host cell.
Although many DNA viruses provide their own DNA polymerase, their nucleic acid can be replicated by the host DNA polymerase.
Like DNA viruses, RNA viruses usually provide their own RNA replicase but may use host enzymes to replicate the viral nucleic acid.
The termination of lysogeny and entry into the lytic cycle usually occurs in response to environmental damage to the host DNA.
If the lambda repressor protein binds to its target operator before a particular operator is used, lysogeny is blocked and a lytic infection is established.
Alternate bases are sometimes used in viral DNA molecules to protect the DNA from degradation by host enzymes.
Once a virus establishes lysogeny, it may not switch to the lytic cycle at some later time.
When a temperate phage enters a cell first, lysogeny is established and then the lytic cycle is entered.
In T4 infection, the first complete infective virions appear about 15 minutes after infection.
The mechanisms for release of bacteriophages without lysing the host cell are not well understood.
Which of the following is true about the attachment of viruses to host-cell receptors?A. Electrostatic interactions help mediate the attachment.B. Attachment is influenced by pH and the presence of ions such as Ca2t and Mg2t.C. Both a and b are correct.D. Neither a nor b is correct.
The tail tube of a complex bacteriophage may interact with the plasma membrane of the host cell to form a pore through which the entire virion enters the cell.
A ______________ is an infected bacterium that is carrying a dormant prophage in the lysogenic state.
Noncapsid proteins that aid in the assembly of virion structures but do not become incorporated into the virion are referred to as ________________proteins.
Which of the following is not used in the classification of animal viruses?A. virus morphologyB. nucleic acid propertiesC. genetic relatednessD. All of these are used in the classification of animal viruses.
Genetic relatedness of viruses is determined byA. nucleic acid hybridization.B. nucleic acid sequencing.C. both nucleic acid hybridization and nucleic acid sequencing.D. neither nucleic acid hybridization nor nucleic acid sequencing.
Which of the following is generally not true of animal viruses?A. The host range may be restricted to a single species.B. The host range may cross species barriers within a single kingdom.C. The host range may cross kingdom barriers.D. The host range may be restricted to certain tissue types within a species.
As a result of viral infection, host macromolecular synthesis may beA. halted.B. unaffected.C. stimulated.D. Any of these.
For which of the following DNA viruses do(es) DNA replication occur in the cytoplasm rather than in the nucleus?A. poxvirusesB. herpesvirusesC. adenovirusesD. DNA replication occurs in the nucleus for all of these.
For DNA viruses, transcription usually uses host RNA polymerase except forA. parvoviruses.B. papovaviruses.C. herpesviruses.D. poxviruses.
Retroviruses use +ssRNA as their genome RNA. In order to complete an infection, they must first make a __________ molecule, which they use to direct the synthesis of mRNA.A. dsRNAB. dsDNAC. DNA:RNA hybridD. -ssRNA
In which of the following stages of the viral infectious cycle do enveloped viruses usually acquire their envelopes?A. penetrationB. component biosynthesisC. assemblyD. release
Which of the following does not represent a way in which animal viruses damage their host cells?A. disruption of lysosomes, releasing hydrolytic enzymes into the cellB. alteration of the plasma membrane so that the cell is attacked by the host immune systemC. formation of inclusion bodies, causing direct physical disruption of cell structuresD. All of these are ways in which animal viruses damage their host cells.
Viral infections in which the virus reproduces at a slow rate without causing noticeable symptoms are referred to as __________ infections.A. persistentB. latentC. slow virusD. None of these.
Progressive, degenerative diseases in which the symptoms build slowly over a period of years are called __________ infections.A. persistentB. latentC. slow virusD. None of these.
A __________ infection is one in which the virus quits reproducing and remains dormant for a period before becoming active again.A. persistentB. latentC. slow virusD. None of these.
The Epstein-Barr virus causesA. Burkitt's lymphoma.B. nasopharyngeal carcinoma.C. infectious mononucleosis.D. All of these.
Which of the following has been associated with a form of liver cancer?A. human papilloma virusB. hepatitis B virusC. human T-cell lymphotropic virusD. hepatitis A virus
Plant viruses require some form of mechanical damage in order to be able to penetrate the tough cell walls of their hosts. Which of the following cannot be used to aid virus entry into the host cells?A. soil nematodesB. parasitic fungiC. insects such as aphids and leafhoppersD. All of these can aid virus entry into host cells.
Viruses of higher fungi are generallyA. dsRNA and cytopathic.B. dsRNA and not cytopathic.C. dsDNA and cytopathic.D. dsDNA and not cytopathic.
Viruses of lower fungi are usuallyA. dsRNA and lytic.B. dsDNA and lytic.C. either dsRNA and lytic or dsDNA and lytic.D. neither dsRNA and lytic nor dsDNA and lytic.
Currently, there is tremendous interest in the use of insect viruses as a means of biological pest control. This is becauseA. insect viruses are invertebrate specific and should, therefore, be safe to use around humans.B. insect viruses have a long shelf life and are environmentally stable.C. insect viruses are suited for commercial production because they reach high concentrations in infected insects.D. All of these.
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. All of these are true of viroids.
Viroids are of economic significance because they cause disease inA. plants.B. animals.C. humans.D. All of these.
Prions are of significance because they cause disease inA. domestic animals.B. humans.C. both domestic animals and humans.D. neither domestic animals nor humans.
Which of the following diseases is (are) caused by prions?A. scrapie (in sheep)B. mad cow diseaseC. scrapie and mad cow diseaseD. neither scrapie nor mad cow disease
The enzyme used by retroviruses to make a DNA copy of their RNA genome is calledA. RNA polymerase.B. DNA polymerase.C. RNA replicase.D. reverse transcriptase.
Genes whose expression (or abnormal expression) causes cancer are calledA. cancer genes.B. progenes.C. oncogenes.D. carcinogenes.
Which of the following does not use RNA as the genome?A. adenovirusB. coronavirusC. togavirusD. paramyxovirus
Which of the following uses dsRNA as the genome?A. parvovirusC. reovirusD. poxvirus
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Which of the following must bring in a virion-associated RNA replicase because the genome is unable to function as mRNA, thereby directing the synthesis of such an enzyme after penetration of the nucleic acid?A. +ssRNA virusesB. -ssRNA virusesC. +dsRNA virusesD. All of these.
The most common type of molecule functioning as an animal virus receptor is aA. lipoprotein.B. glycoprotein.C. phosphoprotein.D. teichoic acid.
Deletion mutations in some viruses produce altered viruses that cannot reproduce and that slow normal virion reproduction. These are calledA. deletion particles.B. replication incompetent viruses.C. defective interfering particles.D. All of these.
Most enveloped viruses use the host __________ membrane as their envelope source; however, it is first modified by the deposition of virus-specific proteins.A. plasmaB. nuclearC. mitochondrialD. None of these.
Unlike most enveloped viruses, herpesviruses involve the host __________ membrane in the formation of their envelope.A. plasmaB. nuclearC. mitochondrialD. None of these.
Which of the following do poxviruses use as their envelope source? A. plasma membrane B. nuclear membrane C. mitochondrial membrane D. None of these.
The most common type of interaction between a virus and its receptor isA. ionic.B. covalent.C. hydrogen bonding.D. hydrophobic.
Virus morphology usually does not include which of the following characteristics?A. sizeB. shapeC. presence or absence of an envelopeD. All of these are included in virus morphology.
Which of the following types of virus usually show more diversity in their reproductive strategies?A. DNA virusesB. RNA virusesC. neither shows any diversityD. both are equally diverse
Poliovirus receptors are foundA. 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.
Which of the following is most used by animal viruses for packaging the genome?A. building the capsid around the nucleic acidB. inserting the nucleic acid into preformed, complete capsidsC. inserting the nucleic acid into preformed, but incomplete capsidsD. All of these are used with equal frequency by various viruses.
Which of the following is not used by animal viruses for packaging the genome?A. building the capsid around the nucleic acidB. inserting the nucleic acid into preformed, complete capsidsC. inserting the nucleic acid into preformed, but incomplete capsidsD. All of these are used by various viruses.
Which of the following is true about adult T-cell leukemia?A. it is one of the most common forms of leukemiaB. it is caused by a retrovirusC. Both of these answers are true.D. Neither of these answers is true.
Which of the following uses ssDNA as the genome?A. parvovirusB. adenovirusC. herpesvirusD. papovavirus
In a retroviral infection when is the proviral DNA integrated into the host chromosome? A. before B. after C. For some viruses it is before, for some viruses it is after. D. For any viruses sometimes it is before and sometimes it is after.
Enveloped viruses may enter their host cells by fusion of their envelope with the cytoplasmic membrane, thereby depositing their nucleocapsid within the cell.
Enveloped viruses may enter their host cells by engulfment within coated vesicles (phagocytosis).
One mechanism by which viruses cause cell damage is by the accumulation of high protein concentrations within the host cell.
The injection mechanism used by bacteriophages whereby the nucleic acid penetrates the cell leaving the protein coat outside, is not used by any known animal viruses.
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.
Almost all known plant viruses are RNA viruses.
Like animal viruses that use an RNA genome, plant viruses must provide a virus-specific RNA replicase because the host cells do not have an enzyme that will replicate RNA.
Viruses infecting algae have never been detected.
Prions are a proteinaceous particle with no apparent nucleic acid genome.
Although picornavirus capsids contain several distinct proteins, these are synthesized as a single polypeptide then cleaved by proteases to produce the individual proteins.
Poxviruses have a complex infectious cycle in which partial uncoating occurs followed by early gene expression. One of these early gene products is an enzyme that completes the uncoating process prior to DNA replication.
Some viruses cause abnormal growth of cells rather than destruction. This is called __________.
Some cancer cells revert to a more primitive or less differentiated state. This is called __________.
__________ infections are those that have a rapid onset and last for a relatively short period of time.
Which of the following statements is true about human T-cell lymphotrophic viruses and leukemia?A. HTLV-1 causes adult T-cell leukemia while HTLV-2 causes hairy-cell leukemia.B. HTLV-1 causes hairy-cell leukemia while HTLV-2 causes adult T-cell leukemia.C. Both HTLV-1 and HTLV-2 cause adult T-cell leukemia.D. Both HTLV-1 and HTLV-2 cause hairy-cell leukemia.
The mechanism of pathogenesis by prions may involve a conformational change in the prion protein (PrP) to an abnormal form.
There are no known human diseases that have been linked to prions.
Which of the following represent(s) the way(s) in which enveloped viruses acquire their envelopes?A. budding through the plasma membraneB. budding through internal cellular membranesC. for some viruses a is correct: for other viruses b is correct.D. neither a nor b is correct.