Microbiology - Viruses, Viroids, and Prions (Ch. 13)

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Microbiology - Viruses, Viroids, and Prions (Ch. 13)
2013-04-18 13:34:09

Microbiology - Viruses, Viroids, and Prions (Ch. 13)
Show Answers:

  1. What is a virus?
    A virus is a tiny infectious acellular agent composed nucleic acid surrounded by proteinaceous capsomeres that form a covering called a capsid.

    (13, 375)
  2. What is a capsid?
    capsid is a protein coat surrounding the nucleic acid core of a virus.

    (13, 375)
  3. What is an envelope?
    An envelope is a phospholipid membrane that surrounds the nucleocapsid.

    (13, 375)
  4. What is a nucleocapsid?
    nucleocapsid is collectively the nucleic acid and its capsid of a virion.

    (13, 375)
  5. What are the four possible types of viral genomes?
    • 1) ssDNA
    • 2) dsDNA
    • 3) ssRNA
    • 4) dsRNA

    (13, 376)
  6. What does is mean if a virus is a generalist?
    If a virus is a generalist, it means it can infect many different kinds of cells in many different hosts.

    (13, 376)
  7. What is a bacteriophage?
    What is another name for it?
    bacteriophage is a virus that infects bacteria.

    It is also known simply as a phage.

    (13, 376)
  8. What is a capsomere?
    Capsomeres are the proteinaceous subunits which comprise the capsid of a virus.

    (13, 377)
  9. What are the three basic viral shapes?
    • 1) Helical
    • 2) Polyhedral
    • 3) Complex

    (13, 377-379)
  10. Where do viruses acquire their envelopes (if they do in fact have an envelope)?
    They acquire their envelope from the host cell. The envelope is a portion of the membrane system of the host cell.

    (13, 379)
  11. What is the lytic replication cycle?
    The lytic replication cycle is a process of viral replication consisting of five stages, ending with lysis of the host cell as well as the release of new virions.

    (13, 382)
  12. What are the five stages of the lytic replication cycle?
    • 1) Attachment of the virion to the host cell.
    • 2) Entry of the virion and its genome into the host cell.
    • 3) Synthesis of new nucleic acids and viral proteins by the host cell's enzymes and ribosomes.
    • 4) Assembly of new virions within the host cell.
    • 5) Release of new virions from the host cell.

    (13, 382)
  13. What is burst time?
    Burst size?
    • Burst time is the time required for a virus to complete its entire process, from attachment to the host cell to release.
    • Bust size is the number of virions released from each lysed host cell.

    (13, 384)
  14. What is the lysogenic replication cycle?
    What is another name for it?
    • The lysogenic replication cycle is a process of viral replication in which the bacteriophage enters a bacterial cell, inserts its DNA into the host, then remains inactive. Thus, every time the bacteria replicates its chromosome, so too does the phage replicate. Later, the phage may leave the chromosome. 
    • It is also known as lysogeny.

    (13, 385)
  15. Temperate phages use what type of replication cycle?
    What is another name for them?
    • Temperate phages are involved in the lysogenic replication cycle.
    • Thus, they are also known as lysogenic phages.

    (13, 385)
  16. What is a prophage?
    prophage is an inactive bacteriophage.

    (13, 385)
  17. What is lysogenic conversion?
    Lysogenic conversion is a process whereby lysogenic phages can change the phenotype of a bacterium, for example from a harmless form into a pathogen.

    (13, 386)
  18. In virology, what is induction?
    Induction is the exision of a prophage from the host chromosome, at which point the prophage reenters the lytic phase.

    (13, 386)
  19. What are three different ways viruses can enter animal cells?
    • 1) Direct penetration
    • 2) Membrane fusion
    • 3) Endocytosis

    (13, 387)
  20. What is uncoating?
    Uncoating is the removal of a viral capsid once it is within a host cell.

    (13, 387)
  21. In viriology, what is budding?
    Budding is the extrusion of virions through a host cell's membrane.

    (13, 389-390)
  22. What are persistent infections?
    • Persistant infections are infections with enveloped viruses in which the host cells shed the viruses slowly and relatively steadily.
    • *This is in direct contrast with lytic replication cylces, where there is a sudden burst of infection.

    (13, 390)
  23. What is latency?
    Latency is a process where an animal virus, sometimes not incorporated into the chromosomes of the cell, remains inactive in the cell.

    *This can occur even for years before the virus becomes active again.

    (13, 391)
  24. What are latent viruses?
    What is another name for them?
    Latent viruses are viruses involved in latency. They are also known as proviruses.

    (13, 391)
  25. Does induction occur in eukaryotes?
    No. When a provirus is incorporated into eukaryotic DNA, the condition is permanent.

    (13, 391)
  26. What is reverse transcriptase?
    Reverse transcriptase is a complex enzyme that allows retroviruses to make dsDNA from RNA templates.

    (13, 388)
  27. What is neoplasia?
    Neoplasia is uncontrolled cell division in a multicellular animal.

    (13, 392)
  28. What is a tumor?
    tumor is a mass of neoplastic cells.

    (13, 392)
  29. What are the two categories of tumors?
    • 1) Benign
    • 2) Malignant (Cancers)

    (13, 392)
  30. What is metastasis?
    Metastasis is the spreading of malignant cancer cells to the nonadjacent organs and tissues, where they produce new tumors.

    (13, 392)
  31. What are protooncogenes?
    What are they called when they are active?
    • Protooncogenes are genes that play a role in cell division.
    • When they are active, they are known as oncogenes.

    (13, 392)
  32. What percentage of cancers are caused by viruses?

    (13, 392)
  33. What are the two types of cell cultures? 
    Briefly explain each one.
    • 1) Diploid cell cultures
    • These are created from embryonic animal, plant, or human cells. They typically last no more than 100 generations (cell divisions) before they die.
    • 2) Continuous cell cultures
    • These are derived from tumor cells and thus provide a never-ending supply of cells (since tumor cells don't know when to stop dividing). 
    • *Henrietta Lacks and HeLa cells (1951)

    (13, 394)
  34. What are viroids?
    Viroids are extremely small, circular pieces of RNA that are infectious and pathogenic in plants.

    (13, 394)
  35. How are viroids different from RNA viruses?
    They lack capsids.

    (13, 394)
  36. What are viroidlike agents?
    They are infectious, pathogenic RNA particles that lack capsids but infect fungi, not plants. Thus, they cannot be considered viroids.

    (13, 395)
  37. What is a prion?
    prion is a proteinaceous infectious particle that lacks nucleic acids and replicates by converting similar normal proteins into new prions.

    (13, 395)
  38. How do prions affect mammals?
    Prions affect a cytoplasmic membrane protein called PrP. The prion changes the functional structure of several prominent alpha-helices into beta-pleated sheets.

    (13, 395)
  39. Due to its affects on the brain, what else are prion diseases referred to as?
    Spongiform encephalopathies.

    (13, 396)
  40. List 7 ways viruses differ from other life forms.
    • 1) Are not cells.
    • 2) Are all obligate intracellular parasites.
    • 3) Have no metabolism outside of the host cell.
    • 4) Do not divide - only propagate by invading the host cell.
    • 5) Have no mechanisms to make proteins (outside of hijacking the host’s
    • mechanisms).
    • 6) Are biologically inert.
    • 7) Do not necessarily have a genome of dsDNA (though some do).

    (Class Notes)