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65 Cards in this Set
- Front
- Back
What is the fundamental difference between viruses and all other infectious agents?
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mechanism of reproduction -- Virus replication is carried out by the host cell machinery, which synthesizes multiple copies of the viral genome and viral proteins.
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What does it mean that viruses are obligate intracellular parasites?
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They have no means to produce energy and contain only a few enzymes at most.
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This type of virus infects bacteria.
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Bacteriophage
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What is a virus particle called?
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a virion
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This single- or double-layer protein shell surrounds the viral nucleic acid.
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capsid
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Viral capsid proteins are arranged in two basic patterns of capsid structural symmetry, icosahedral and helical. What is the difference between the two?
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Icosahedral symmetry contains a defined number of structural subunits, whereas the number of subunits varies in viruses with helical symmetry.
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Human viruses with helical symmetry invariably have DNA or RNA genomes?
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RNA
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This is composed of virus-specific proteins plus lipids and carbohydrates derived from host cell membranes and covers the nucleocapsid.
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envelope
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These proteins sometimes line the inner surface of the envelope and stabilize the interaction between viral glycoproteins and the lipid envelope, direct the viral genome to intracellular sites of virus assembly, or help in virus budding.
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M proteins
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What are virus-specific envelope glycoproteins that protrude from the outer surface of the envelope called?
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spikes
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Retroviruses contain an RNA-dependent DNA polymerase known as what?
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reverse transcriptase
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What are the four major steps in virus replication?
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1. Infection of a susceptible cell
2. Reproduction of the nucleic acid and proteins 3. Assembly and 4. release of infectious progeny |
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The attachment of the virus to the host cell surface is known as what?
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adsorption
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For enveloped viruses, what is the usual attachment protein?
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one of the spikes on the outside of the viral envelope
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For nonenveloped virsues, what proteins serve as the attachment sites?
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exposed regions of capsid proteins
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T/F Viruses of the same species but different serotypes can bind to the same receptors or different ones.
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True
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What are the two major methods that nonenveloped viruses pass into the cell?
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receptor-mediated endocytosis and direct crossing of the plasma membrane
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What are the two major methods that enveloped viruses pass into the cell?
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1. Endocytosis within clathrin-coated vesicles.
2. Direct fusion with the plasma membrane. |
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What is the step called in which the viral delivery system is removed to make the viral genome accessible?
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uncoating
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These viruses allow for the nucleic acid of the virion to function directly as mRNA.
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Single-stranded positive-sense RNA viruses (e.g. poliovirus, west nile virus)
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Briefly describe positive-sense RNA replication.
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RNA polymerase synthesizes a negative-sense RNA which serves as the template for the synthesis of additional copies of genomic positive-sense RNA.
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What important intermediate step is needed for protein synthesis in single-stranded negative-sense viruses?
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The production of the complement positive strand of RNA (this functions as mRNA). Because human cells do not have RNA-dependent RNA polymerase (until 9 days ago), the virus must carry its own.
http://www.futurity.org/science-technology/human-cells-copy-dna%E2%80%94and-rna-too/ |
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Briefly describe negative-sense RNA replication.
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RNA polymerase synthesizes a positive-sense RNA which serves as the template for the synthesis of additional copies of genomic negative-sense RNA.
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How do retroviruses replicate?
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Viral positive-sense RNA serves as a template for a virion-associated RNA-dependent DNA polymerase (reverse transcriptase). The DNA is then integrated into host chromosomal DNA, where it resides for the life of the cell.
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With DNA viruses, early transcripts encode what kind of proteins?
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Regulatory and the proteins involved in DNA replication
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With DNA viruses, late transcripts encode mainly what kind of proteins?
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structural
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When are nonenveloped viruses usually released?
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During cell lysis
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How are enveloped viruses usually released?
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cell budding
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When viruses enter host cells, virus-encoded proteins are inserted into host cell membranes. What protein serves as a binding site to some intracellular viral capsids aiding in their release?
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M proteins
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Cell shrinkage, membrane blebbing, condensation of nuclear chromatin, and cleavage of cellular DNA are characteristics of what?
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apoptosis
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What makes "defective viruses" defective?
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They require coinfection with a "helper" virus to replicate
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Coinfection with what two viruses frequently results in fulminant hepatitis?
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hepatitis delta virus and hepatitis B virus
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These transmissible agents consist of "infectious proteins" and are devoid of nucleic acid.
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prions
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Name four neurologic diseases caused by prions.
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1,2. Creutzfeldt-Jakob disease and kuru in humans.
3. scrapie in sheep 4. bovine spongiform encephalopathy "mad cow disease" |
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Prion protein PrPsc is very similar to the normal cellular protein PrPc. PrPsc can function as a template, forcing PrPc to assume the PrPsc conformation. With what three methods can prion-infected material be transmitted?
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1. direct inoculation into the CNS
2. percutaneous exposure 3. ingestion |
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Spongy cavitations in the brain is a characteristic pathological sign of prion disease, also referred to as...
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transmissible spongiform encephalopathies
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In this type of infection, the virus undergoes multiple rounds of replication which results in the death of the host cell.
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acute infection
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In this type of infection, which are caused by DNA viruses or retroviruses, progeny are not produced.
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latent infection
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In this type of infection, virus particles continue to be shed after the period of acute illness.
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chronic infection
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Give three examples of respiratory viruses and their method of transfer.
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1. varicella-zoster virus - small droplets
2. Epstein-Barr virus - saliva 3. Rhinovirus - contaminated hands to eyes, nose or mouth |
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Because of the presence of bile salts, many GI viruses are enveloped or nonenveloped?
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nonenveloped
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horizontal spread
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person to person
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vertical spread
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mother to fetus
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The period of time when viral replication occurs before any signs or symptoms of clinical illness or evident.
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incubation period
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Give three examples of viruses that spread through nerves.
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HSV, rabies, VZV
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What is the only place in the body where the nervous system is in direct contact with the environment.
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olfactory system
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Where is the typical site of primary replication for enteric virsues (2)?
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Peyer patches and peritonsillar lymphatic tissue
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Where does primary replication usually occur in respiratory viruses (2)?
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epithelial or alveolar cells
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These three viruses travel free within plasma.
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1. Enteroviruses
2. HBV 3. togaviruses |
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These two viruses are associated with RBCs.
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1. Colorado tick fever
2. Rift Valley fever |
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These four viruses are associated with lymphocytes or monocytes.
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1. CMV
2. EBV 3. HIV 4. Rubella |
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What is the most important adaptive defense mechanism against viral infections?
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cell-mediated immunity
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Out of the following: antibodies, neutrophils and macrophages, which are most involved in virus containment.
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macrophages
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Because of the viral intracellular habitat, infected cells are susceptible to the action of lymphocytes that recognize viral antigens bound to what proteins on their surface?
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MHC
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Cytotoxicity by what cells provides one of the earliest host defenses against viral infection?
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NK cells
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Antibodies that protect the host by destroying the infectivity of the virus are called what?
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neutralizing antibodies
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If two isolates of a virus are neutralized by the same specific antibody, they are said to belong to a single what?
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serotype
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What is the mechanism behind antibody-dependent cell-mediated cytotoxicity (ADCC)?
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Virus-specific antibodies bound to antigens on the surface of infected cells interact with receptors for the Fc portion of IgG on the surface of NK cells thus activating the NK cells and resulting in target cell killing.
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The synthesis of these proteins is induced by viruses and other proinflammatory agents.
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interferons
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What is the mechanism by which interferons inhibit virus replication?
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Indirectly by inducing the synthesis of cellular proteins that inhibit the protein synthesis machinery.
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This type of interferon is produced by leukocytes.
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alpha
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This type of interferon is produced by fibroblasts and epithelial cells.
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beta
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This type of interferon is induced by the activation of T cells by specific antigens.
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gamma
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Does interferon tend to act locally or systemically?
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locally
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Do viruses trigger the activation of the complement system?
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yes, BUT the complement system is not likely to be essential for defense against viral infections.
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