Micro Ch 13

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Micro Ch 13
2011-03-17 12:15:55
Microbiology Viruses

Review questions from Micro ch 13 on Viruses
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  1. What is the structure of a virus?
    1. DNA or RNA - not both - both can be single or double stranded.

    2. Capsid = protective protein coat - made of capsomeres

    3. Envelope - not all viruses have it

    4. Spikes - some have spikes for attachment to host
  2. Are viruses alive?
    Are viruses specific?
    What is Host Range?
    Viruses are obligatory intercellular parasite - they cannot reproduce outside of a host cell and thus are not classified as alive.

    Virsus are very specific - most often can only infect 1type of cell in 1 species -not always the case (bird flu/ swine flu)

    Host Range - spectrum of host cells the virus can infect - this is determined by specific host attachement sites
  3. What size are viruses?
    What are the shapes of viruses?
    Most are much smaller than bacteria. They range in size from 30 nm (nanometers) to 1 um (micrometer) - (most bacteria are 1 um in size

    • Viral shapes are determined by the capsid
    • 1. helical - hollow protein capsule hold DNA or RNA
    • 2. polyhedral - icosahedral = 20 sided equilateral triangle faces
    • 3. enveloped - only in some - some have spikes on envelope that can mutate (influenza) - roughly spherical
    • 4. complex - bacteriophage: head (capsid), body (sheath), legs (fibers)

  4. What is a bacteriophage?
    What is a Virion?
    • A complex virus that affects only bacteria - also called phages
    • -on culture plate - they form plaques on a lawn of bacteria

    Virion = fully assembled virus
  5. List 3 ways viruses are grown for study.
    Virsues must be grown in living cells:

    • 1. Living animals (living cells of host)
    • 2. Embryonated eggs (living cells of host)
    • 3. Cell cultures (1 living cell type)
  6. Serological tests
    can be used to diagnose viral infections in man - Known viral antigen are mixed with patients serum to detect antibodies against the virus.

    • Detection is not always easy becuase most viruses are inside the cell (not in the bloodstream)
    • Western blot test is used to confirm HIV infection - looks at serum antibody binding to prepared HIV proteins.
  7. 5 stages of bacteriophage replication (Lytic cycle)
    What is the lytic cycle?
    What is the lysogenic cycle?
    • 1. Attachment - phage attaches by tail fibers to host cell
    • 2. Penetration - phage tail releases lysozyme to break open cell wall → sheath contracts → tail core (pin) driven into cell wall → DNA injected into cell (cuspid stays outside)

    3. Biosynthesis - of phage DNA and proteins - using host cell machinery

    4. Maturation - assembly of phage particles into virions (complete viral particle)

    5. Release - phage lysosome lyses cell wall - virus released and cell dies

    Lytic cycle - phage replication results in lysis and death of cell

    Lysogenic cycle = Prophage (instead of Biosynthesis) - DNA is incorporated in host DNA and then is replicated with each cell division (host cell lives on)

    a bacteriophage can do either or both at the same time
  8. Viral Replication
    Viruses use host cell's machinery to replicate itself

    Virus make thousands of itself within 1 cell when it replicates

    Host cell either dies (lysis) or lives indefinately to reproduce the virus (HIV integrates itself into host cell genome)
  9. What are the differences in animal vrial replication and bacteriophage?
    • Penetration - by endocytosis - entire viron enters cell
    • Uncoating - of cuspid proteins (by viral or host enzymes)

    • 1. Attachement
    • 2. Penetration - endocytosis
    • 3. Uncoating
    • 4. Biosynthesis
    • 5. Maturation
    • 6. Release - by rupture (lysis) or budding (enveloped virus)
  10. One step growth
    What is the eclipse period?
    One step growth - virions present in culture until attachment - then no new virons are found in the culture until after biosynthesis and maturation have taken place. Most infected cells die as a result of infection- consequently, new virions will not be produced.

    • The eclipse period is the time between infection of the cell and the appearance of the mature virus within the cell.
  11. What is a provirus vs. a prophage?
    Provirus - a piece of viral DNA that is integrated into a host cell chromosome - the provirus never comes out of the chromosome- thus it is protected from the host's immune system and antiviral drugs

    Prophage - phage DNA inserts itself in the circular bacterial DNA - every time the cell replicates, it replicates the phophage DNA also. Some future even will cause the phage DNA to pop out and initiate the lytic cycle
  12. Why is HIV a "retro" virus - describe its replication.
    What is reverse transcriptase?
    Does HIV form a "provirus"?
    • HIV = Human Immunodeficiency virus
    • 1. HIV virus enters a human T-cell
    • 2. uses reverse transcriptase (an enzyme) to copy its RNA into double straded DNA
    • 3. DNA then inserts into T-cell DNA -PROVIRUS
    • 4. Provirus - always stays inserted - replicates with T-cell division - can turn on at future point and reproduce itself in numbers

    RETRo virus - name comes from REverse TRansscriptase

    Retrovirus is derived from the name REverse TRanscriptase - the enzyme that
  13. What is budding?
    Budding is one method of release of an virus from the host cell (animal only) - The assempled capsid (containing nucleic acid) is pushed through the plasma membrane of the host cell - The plasma membrane adheres to the virus and form the envelope which pinches off the host cell
  14. What is an oncogenic virus?
    An oncogene - where is it located? what turns it on?
    Oncogenic virus = cancer causing virus

    Oncogenes - mutant host cell regulatory genes that can cuase cancer when turned on by a oncogenic virus

    all oncogenic viruses integrate themselves into host DNA
  15. Transformed
    a transformed cell is a host cell that is infected by an ongogenic virus and turns into a tumor cell
  16. Latent viral infection
    persistent viral infection
    Latent - virus remians asymptematic for long periods of time - chickenpox/ shingles, herpes 1 (cold sores)
  17. Papillomavirus
    • DNA virus
    • veneral warts - cervical cancer

    • 100 different HPVs
    • - replicate on body surface cells (skin/ mucosa)
    • - vaccine
  18. Hepatitis B virus
    • DNA virus
    • Infects the hepatocyte - cell lysis
    • Acute Hepititis B viral - usually self-limited

    • Chronic active hepititis → cirrhosis of the liver
    • can cause hepatoma (cancer)

    • Rx - interferon (chronic acive hep)
    • Drug induced hepititis
  19. Cause the common cold
    Adenovirus, rhinovirus, coronavirus
  20. Poxvirus
    • smallpox - DNA
    • 30% mortality - to Rx exists -
    • can vaccinate up to 3 days after exposure
    • pheumonia, encephalitis, corneal ulceration (blindness)

    Cowpox = original vaccine (milk maids)
  21. Herpes Virus
    • DNA
    • 1. Herpes simplex I - oral
    • 2. Herpes simplex II - genital - both inhibit DNA polymerase
    • 3. Varicella zoster - chickenpox - lives in sensory neurons
    • 4. Kaposi's sarcoma - viral cancer (AIDS dd)
    • 5. Epstein-Barr virus - mononucleosis, Burkitt's lymphoma
  22. Poliovirus
    • RNA
    • infects motor neurons - flaccid paralysis
  23. Rubellavirus
    • RNA
    • Rubella - german measels
    • -fetal abnormalities if mother infected during 1st trimester
    • MMR vaccine
  24. Rhabdovirus
    • RNA
    • rabies -
    • death from respiratory failure or acute enchehilitis (travels to brain along peripheral nerves)
    • ANY mammel can get it
    • 100% mortality once symtomatic
    • post exposure vaccination is effective
  25. Paramyxovirus
    • RNA virus
    • RSV - respiratory syncytial virus - infant bronchoilitis

    • Parainfluenza - croup (laryngotracheobronchitis)
    • - bronchoilitis

    Mumps - infects parotid gland & testes - vaccine

    measels - vaccine
  26. Influenza
    • RNA enveloped virus - A, B, C
    • antigenic shirt - major change
    • antigenic drift - minor change
    • spikes mutate often - new vaccine every year
  27. Lentivirus
    • RNA retrovirus - HIV (Human Immunodeficiency Virus)
    • uses its own reverse transcriptase (singel stranded RNA → double stranded DNA)