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2011-05-08 23:13:11


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  1. ch 13/14
  2. 1. *Describe in detail the 5 stages of animal virus life cycles. Be able to differentiate between biogenesis stages of the different types of animal viruses.
    • Adsorption (Attachment)
    • ¥ The phage collide by chance with the bacteria
    • ¥ The base plate with its tail spikes settles on the surface of the bacterium
    • ¥ The phage use these structures for their own purposes
    • Penetration
    • • Entrance of the virus OR its nucleic acid in the host cell
    • • Plant and bacteria viruses inject the nucleic acid into the host through the cell wall
    • • Animal viruses enter the cell whole
    • • Animal cells have no rigid cell wall
    • • Penetration of the virus is through:
    • • Phagocytosis in which the virus is engulfed by the cell
    • • Membrane fusion occurs with enveloped viruses when the viral envelope fuses with the plasma membrane of the host cell
    • • Viruses enter intact but require an uncoating step to release the nucleic acid from the protein coat
    • Transcription/Replication Lytic Cycle
    • • Duplication of viral components
    • • During replication:
    • • Virus will inhibit activity of the host DNA
    • • Virus produces enzymes to destroy host DNA
    • • Viral DNA takes over and begins producing proteins
    • • Early viral proteins are synthesized and are associated with the replication of viral nucleic acid
    • • Late viral proteins are synthesized and are associated with the replication of other viral structures
    • Assembly
    • • This stage is the assembling of the replicated viral components into an intact, mature virus
    • • The protein structures of the phage such as the tail, heads, and tails (sheaths), tail spikes and tail fibers are synthesized independently of one another
    • Release
    • • Host cell bursts and releases viruses to the outside environment
    • • Viruses are now extracellular
    • • As viruses leave the host cell, the envelope is picked up
    • • The envelope is made of a portion of the host cell plasma membrane which becomes the lipid envelope of the virus
  3. 2. What is the major difference in the entry of animal viruses and bacterial viruses into their host cells?
    Bacterial viruses adsorb and firmly attach to the surface of the bacterium and then penetrate the rigid cell wall, transmitting the viral nucleic acid into the host. Animal viruses enter host cells by a process called endocytosis
  4. 3. Examples of viruses with each type of nucleic acid.
    ds RNA (ebola virus), ss ddRNA(poliovirus), ds DNA(hpv), ss DNA(herpes simplex virus )
  5. How are viruses classified?
    Groupings based on route of transmission, Disease-causing viruses often grouped by route of transmission,
  6. 4. Describe the routes of viral transmission and give an example of each.
    • Enteric viruses, Generally transmitted via fecal-oral route, Often cause gastroenteritis, Some can cause systemic disease,
    • Respiratory viruses: Usually inhaled via infected respiratory droplets, Generally remain localized in respiratory tract
    • Zoonotic viruses: Transmitted from animal to human via animal vector
    • Sexually transmitted viruses: Can cause lesions on genitalia or cause systemic infections
  7. 5. Describe an acute viral infection and the different types of persistent and latent viral infections, giving examples of viruses that follow each pattern. 
An acute viral infection is characterized by rapid onset of disease, a relatively brief period of symptoms, and resolution within days. It is usually accompanied by early production of infectious virions and elimination of infection by the host immune system. Acute viral infections are typically observed with pathogens such as influenza virus and rhinovirus.
  8. 6. What is the difference between a latent and an active infection?
    • Latent infections
    • Infection is followed by symptomless period, then reactivation, Infectious particles not detected until reactivation, Symptoms of reactivation and initial disease may differ (Example: Herpes simplex viruses 1 and 2 (HSV1 and HSV2), Shingles (zoster))
    • Chronic infections
    • Infectious virus can be detected at all times
    • Disease may be present or absent during extended times or may develop late
    • Best known example Hepatitis B, a.k.a serum hepatitis
  9. 7. Various effects of animal viruses on the cells they infect.
    They can cause acute or persistent infections
  10. 10. Describe how the following types of viruses are released from their host cell.
    • Naked viruses Virus that only has the protein capsid covering it.
    • Enveloped viruses virus covered in a lipid membrane that’s surrounds the protein coat.
    • Phage: shortened term for bacteriophage
  11. 1. Describe generalized and specific transduction.
    Generalized transduction any type of bacteria can be transferred. Specialized transduction only a few specific genes can be transferred
  12. 2. List and describe the three major categories of persistent viral infections giving specific examples of each.
    • Latent infections
    • Infection is followed by symptomless period, then reactivation
    • Infectious particles not detected until reactivation
    • Symptoms of reactivation and initial disease may differ
    • Examples: Herpes simplex viruses 1 and 2 (HSV1 and HSV2), Shingles (zoster)
    • Chronic infections
    • Infectious virus can b6e detected at all times
    • Disease may be present or absent during extended times or may develop late
    • Best known example: Hepatitis B, a.k.a serum hepatitis
    • Slow infections
    • Infectious agent gradually increases in amount over long period of time
    • No significant symptoms apparent during this time
    • Two groups of infectious agents cause slow infections
    • Retroviruses which include HIV
  13. 1. Define:
    • Tumor or neoplasm: abnormal mass of tissue
    • Oncogenes: Gene whose activity is involved in turning a normal cell into a cancer cell.
  14. 2. Describe the role of viruses in the formation of tumors.
    • Double-stranded DNA viruses responsible for most virus-induced tumors in humans
    • Tumor viruses interact with host cells in one of two ways:
    • Virus can go through productive cycle and lyse cell
    • Virus can transform cell without killing it
    • Cancers caused by DNA viruses result from integration of viral genome onto host DNA
    • Transformed genes are expressed
    • Uncontrolled growth results
  15. 3. List three viruses that are associated with tumors in humans.
    HPV-Human Papilomaviruses, Hepatitis B, Hep C, Epstein-Bar
  16. 4. Define host range and the two factors that decide it.
    Number of different bacteria that phage can infect termed host range. Usually limited to single bacterial species for a single phage. 2 factors that decide: phage must be able to attach to host receptors and Restriction-modification systems the host cell must overcome
  17. 5.What are Prions? What disease they cause? How do they differ from viruses?
    Prions: Proteinaceous infectious agent, Linked to a number of fatal human diseases…such as MAD COW Disease. All afflictions cause brain degeneration, Brain tissue develops sponge-like holes, Disease termed transmissible spongiform encephalopathies, Symptoms may not appear for years after infection Apparently arose following gene encoding normal prion protein. Mutation caused protein to have DIFFERENT FOLDING properties, Mutated protein resistant to proteases, Normal protein sensitive, resists UV light and nucleases, Due to lack of nucleic acid, Inactivated by chemicals that denature proteins

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