Microbiology Test II ch13 – Flashcards
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The envelope found in some virus particles differs from the cytoplasmic membrane of cells in that
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it does not perform the physiological functions carried out by the cytoplasmic membrane.
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The combination of a virus's protein coat and nucleic acid core is called the ________.
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nucleocapsid
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Which of the following statements concerning viruses is FALSE?
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Viruses enter a cell to complete the replication they have begun extracellularly.
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The outermost layer of a virion fulfills which of the following functions of the virus?
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protection and recognition
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Most viruses cannot be seen by light microscopy. T or F
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T
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During the intracellular state, a virus exists as
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a nucleic acid.
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Protozoa are susceptible to viral attack. T or F
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T
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Viruses are primarily classified according to their
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type of nucleic acid.
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Host specificity of a virus is due to
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interactions between viral and cellular surface molecules.
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An animal virus that does not have an envelope is described as a(n) ________ virion.
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naked
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Proteins are present in
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both cells and viruses
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Cytoplasm is characteristic of
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cells only
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A lipid membrane is present
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in both cells and viruses.
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In which stage is the viral DNA introduced into the cell?
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Penetration
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In which stage does formation of mature viruses occur?
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Assembly
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The host DNA is usually degraded during which stage?
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Biosynthesis
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What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?
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The virus would not be able to infect new hosts.
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Lysogenic viral DNA integrating into the host genome is referred to as
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a prophage
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Which of the following events might trigger induction of a temperate bacteriophage?
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Exposure to UV light
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How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?
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The host dies during the lytic stage
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What is the fate of the prophage during the lysogenic stage?
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It is copied every time the host DNA replicates.
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How are viruses different from cells?
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They require a host in order to reproduce.
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What is the function of the structural elements of a virus?
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To package and protect the viral genome
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We sometimes are able to generate antibodies (immune system proteins) that bind to and cover up some of the proteins on the outermost portion of a virus while it is in the bloodstream. This renders the virus unable to reproduce. Which step of viral replication are antibodies directly preventing?
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attachment
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Enveloped viruses have a layer of lipids surrounding their capsid. This envelope is made mostly of host cell membrane. In which step does the virus acquire this envelope?
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release
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What occurs during viral uncoating?
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The capsid breaks apart, releasing the viral genome.
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Bacteriophage genes that cause toxin production in a normally harmless bacterial species contribute to which of the following?
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lysogenic conversion
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Infections with enveloped animal viruses are similar to lysogenic phage infections because
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the infected cell may live for a long time
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Which of the following is the midpoint of a lytic replication cycle?
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synthesis
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Lysozyme is important for which of the following stages of lytic replication in bacteriophage T4?
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entry and release
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You have isolated a specimen of lambda phage in which the protein that suppresses prophage genes has suffered a significant mutation. Which of the following would you expect to observe in cultures of this virus?
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The phage will never enter a lysogenic cycle.
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A phage T4 particle that has lost its tail fibers will have a replication cycle that is blocked at which of the following stages
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attachment
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Bacteriophages use the enzyme ________ to breach the bacterial cell wall.
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lysozyme
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The number of new bacteriophages released from each infected cell is called the ________.
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burst size
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Bacteriophages are cheaper and easier to culture than animal viruses T or F
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T
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Another term for a lysogenic phage is a ________ phage
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temperate
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Bacteriophage release is a gradual process in which small numbers are released at a time. T or F
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F
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Poxvirus is assembled in the cytoplasm of the cell instead of in the nucleus, as is the case for the majority of dsDNA viruses. T or F
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T
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RNA viruses such as HIV require the activity of ________ to become proviruses.
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reverse trancriptase
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Put the following stages of a lytic replication cycle in order, from earliest to latest stages: I. Synthesis II. Assembly III. Attachment IV. Release V. Entry
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III. attachment V. entry I. synthesis II. assembly IV. release
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Which of the following is associated with the attachment of a bacteriophage to a bacterial cell?
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random collisions, chemical attractions, and receptor specificity
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The enzyme lysozyme is critical for which of the stages of a bacteriophage T4 infection cycle?
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entry and release
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The phenomenon of transduction is associated with which of the stages of a bacteriophage infection cycle?
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assembly
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Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but not in the lysogenic cycle?
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digestion of host DNA
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Why is lysogeny advantageous to a bacteriophage?
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the genetic material of the bacteriophage can be passed on to future generations of cells.
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Which of the following agents is capable of inducing conversion of a prophage back to a lytic phage?
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UV light and X rays
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Viruses are shed slowly and steadily during
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persistent infection
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During _________, viruses remain dormant in a cell.
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latency
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Virus replication results in the death of the cell in a(n) ________ infection.
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lytic
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_________is a mechanism of release for enveloped viruses.
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budding
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Which of the following would be an appropriate mode of action for a new anticancer drug?
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inactivation of an oncogene
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Both viruses and carcinogenic chemicals can cause tumors by
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disrupting cell division controls.
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Viruses cause most human cancers. T or F
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F
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________, genes that play a role in proper cell division, may also play a role in some types of cancer.
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Protooncogenes
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Tumors invade other organs and tissues in a process called
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metastasis.
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Virus infection results in cancer in the process of
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oncogenesis
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A(n) ________ is a clear zone on a bacterial lawn where cells have been killed by the activity of a bacteriophage.
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plaque
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Zones of clearing in cell cultures that are the result of virus infection are called plaques. Sometimes "cloudy plaques" are seen on bacterial cultures infected with bacteriophage. What type of viral infection might cause this appearance?
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lysogenic
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The normal function of the PrP protein in mammals is believed to be:
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assisting in normal synaptic development and function.
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How do normal prion proteins (PrP) differ from the infectious prion proteins?
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Normal PrP have alpha-helices; infectious PrP have beta-pleated sheets.
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How does the number of infectious prions increase?
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Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.
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Why are the beta-pleated multimers of PrP potentially pathogenic?
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The multimers are more stable and resistant to protease.
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Which of the following prion diseases is found in deer and elk?
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Chronic wasting disease
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Which of the following prion diseases was also known as laughing disease?
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Kuru
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Which of the following conditions in humans is linked to bovine spongiform encephalopathy?
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Variant Creutzfeldt-Jakob disease
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What part of the nervous system is most affected by fatal familial insomnia?
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Thalamus
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Where does the name "scrapie" come from?
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The prion disorder causes infected sheep to scrape against objects until their skin is raw.
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From which phrase is the term "prions" derived?
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Proteinaceous infectious particles
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In what year did Stanley Prusiner discover prions?
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1982
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Which disease did Stanley Prusiner first identify as being caused by prions?
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Scrapie
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How are prions different from other infectious agents?
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They lack nucleic acid.
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Which of the following diseases is NOT caused by prions?
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Hodgkin's lymphoma
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Many diseases of plants are caused by infectious RNA molecules lacking capsids. T or F
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T
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Which of the following infectious particles do not have protein in their structure?
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viroids
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Prions are composed of a single protein called ________.
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PrP
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How are prions different from all other known infectious agents?
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they lack nucleic acid.
