BIOL 2420 Exam4

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manisha
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120197
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BIOL 2420 Exam4
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2011-12-08 23:00:59
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BIOL 2420
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Virus
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  1. 5 Virus characteristics
    • 1. Obligate intracellular parasites
    • 2. Filterable, smaller than bacteria
    • 3. Contain DNA or RNA as genetic material 4. Reproduce by assembly only inside another cell
    • 5. Lack enzymes to produce ATP
  2. Virus Structure
    •Protein coat or capsid

    •Genome = Nucleic acids with or without associated polymerase enzymes

    •With or without surrounding lipid membrane (Enveloped or naked)
  3. Virus Morphology
    • •Polyhedral
    • •Helical
    • •Complex
  4. Classification of virus

    (3 criteria)
    • •Nucleic acid type
    • –DNA, RNA, ds versus ss (+ve or -ve sense), circular or linear, single chromosome or segmented
    • •Morphology
    • –E.g. Capsid structure, size, presence or absence of envelope
    • •Family, (genus), species
  5. DNA Organizational Structure
  6. RNA Organizational Structure
  7. Steps for Virus Reproduction
    • 1. Attachment/absorption
    • 2. Entry/penetration
    • 3. Uncoating (only in animal viruses)
    • 4. Synthesis
    • 5. Reassembly
    • 6. Release from cell
  8. Cycle of Infection and Replication
  9. How does Lysogenic cycle differ from lytic cycle?
    • 1. Recombination of viral nucleic acids into the chromosome of the host acting like a transposon (prophage).
    • 2. Production of repressors for the synthesis of viral sequences during lysogeny.
    • 3. Lytic cycle switch with cell stress and damage e.g. UV or chemical exposure
  10. How are viruses identified in the lab?
    • •Electron microscopic morphology
    • •Physical properties
    • •Antigenic properties: Antibodies to specific proteins of different viruses
    • •Genetic techniques
    • –Hybridization with specific nucleic acid probes
    • –Restriction digest profiles
  11. What determines the Host range of viruses?
    • •Presence of specific proteins or glycoproteins on the surface of the virus particle
    • •Binds specific receptors on susceptible host cells
    • •Cellular enzymes that support viral reactions
  12. How do you culture of viruses?
    • •Grow in living cells in culture
    • –Cell lines generated from different kinds of tissues adapted to growth in culture
    • •Living animals
    • –Chicken embryos or other lab animals
  13. How is the reproduction of animal virus different from that of bacteriophage?
    • •1. Entry of animal virus include capsid. Just the nucleic acid in phages
    • –Entry methods include
    • •Fusion
    • •endocytosis
    • •2. Uncoating of nucleic acid is necessary for the animal viruses
    • –In the cytoplasm (RNA viruses) or nucleus (DNA viruses)
  14. What determines the differences if the pathways of viral multiplication?
    • •Multiplication cycle depends of the genetic material of the virus
    • •1. Type of nucleic acids
    • –DNA or RNA,
    • •2. Single stranded (ss) or double stranded (ds)3. If ssRNA, positive or negative sense
  15. What is the cell damage by viruses?
    • •1. Cell death and lysis
    • •2. None
    • –Persistent production of enveloped virus
    • –Latent prophage/provirus
    • •3. Transformation - altered behavior of cells
  16. 5 Types of infection by viruses
    • •Acute
    • •Chronic/persistent
    • •Slow infections
    • •Latent
    • •Cancer
  17. How can some virus cause cancer?
    • •Integration of DNA at randoms sites on host genome
    • •Encode oncogenes
    • –Such as tumor suppressors (cell cycle inhibitors)
    • –Mutated forms of cell cycle proteins or cell division activator proteins
  18. What is the Major Immune Defense against viruses?
    • •1.Antibodies
    • –Neutralization of virus attachment and hence reduce spread
    • –Activation of destruction by phagocytes and complement (enveloped) or NK cells
    • • 2. Tc or Td killing of virus infected cells - main process of virus clearance
  19. Prions
    -Prions contain protein only


    -Examples of prion-caused human diseases are Kuru, Creutzfeldt-Jakob disease and Gerstmann-Straussler syndrome.

    -Prions also cause scrapie in sheep.

    • -Bovine spongiform encephalopathy (BSE)
    • or Mad Cow
  20. Viroids
    • -RNA only
    • -Does not code for any proteins
    • -Replicated in cells to large amounts overwhelming host (RNA polymerase)
    • -Silencing RNA?
  21. Hepatitis D >delta agent
    • -only known human viroid disease
    • -enclosed in a hepatitis B virus capsid.
    • -simultaneous infection with both the hepatitis B virus and the hepatitis D viroid
    • -D viroid causes liver cell death via sequestering this 7S RNA and/or cleaving it.

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