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USMLE Step I Microbiology > Virology--structures, genetics, vaccines, viral genomes, viral replication, viral envelopes > Flashcards

Virology--structures, genetics, vaccines, viral genomes, viral replication, viral envelopes Flashcards

1
Q

name the structures of a naked virus with a icosahedral capsule

A
  • capsid
  • nucleic acid
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2
Q

name the structures of a enveloped virus with icosahedral capsid

A
  • surface protein
  • lipid bilayer
  • capsid
  • nucleic acid
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3
Q

name the structures of an enveloped virus with helical capsid

A
  • surface protein
  • lipid bilayer
  • hilical nucleocapsid with integrated RNA
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4
Q

explain recombination

A
  • exchange of genes between 2 chromosomes by crossing over within regions of significant base sequence homology
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5
Q

explain reassortment

A
  • when viruses with segmented genomes (ie. influenza virus) exchange genetic material
    • example: novel H1N1 influenza A pandemic emerged via complex viral reassortment of genes from human, swine, and avian viruses
    • has potential to cause antigenic shift
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6
Q

explain complementation

A
  • when 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein, the nonmutated virus “complements” the mutated one by making a functional protein that serves both viruses
    • example: hepatitis D virus requires the presence of replicating hepatitis B virus to supply HBsAg, the envelope protein for HDV
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7
Q

explain phenotypic mixing

A
  • occurs with simultaneous infection of a cell with 2 viruses
  • genome of virus A can be partially or completely coated (forming pseudovirion) with the surface proteins of virus B
  • type B protein coat determines the tropism (infectivity) of the hybrid virus
  • however, the progeny from this infection have a type A coat that is encoded by its type A genetic material
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8
Q

live attenuated vaccines–mechanism

A
  • induce humoral and cell mediated immunitybut have reverted to virulence on rare occasions
  • no booster needed for live attenuated virus
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9
Q

which vaccines are LIVE attenuated vaccines?

A
  • smallpx
  • yellow fever
  • rotavirus
  • chickenpox (VZV)
  • Sabin polio virus
  • Influenza (intranasal)
    • “Live! One night only! See small yellow rotating chickens get vaccinated with SabinandMMR!It’sincredible!”
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10
Q

live vaccines and immunocompromised patients

A
  • dangerous to give live vaccines to immunocompromised patients
    • close contacts may be vaccinated with live vaccines (except live polio or influenza)
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11
Q

MMR vaccine

A
  • measles, mumps, rubella
  • live attenuated vaccine that can be given to HIV + patients who do not show signs of immunodeficiency
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12
Q

killed vaccines–mechanism

A
  • killed/inactivated vaccines induce only humoral immunity but are stable
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13
Q

which vaccines are Killed vaccines?

A
  • Rabies
  • Influenza (injected)
  • Salk Polio
  • HAV
    • “SalK = Killed”
    • “RIP Always”
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14
Q

which vaccines are subunit vaccines?

A
  • HBV (antigen = HBsAg)
  • HPV (types 6, 11, 16, and 18)
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15
Q

which DNA viruses are double stranded?

A
  • all DNA viruses are double stranded
    • EXCEPT Parvoviridae
      • “all are dsDNA (like our cells), except “part-of-a-virus” (parvovirus) is ssDNA”
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16
Q

which DNA viruses are linear?

A
  • all are linear except papilloma-, polyoma-, and hepadnaviruses (circular)
17
Q

which RNA viruses are single stranded?

which RNA viruses are + stranded?

A
  • all RNA viruses except Reoviridae are ssRNA
    • stranded RNA viruses:
      • “I went to a retro (retrovirus) toga (togavirus) party, where I drank flavored (flavivirus) Corona (coronavirus) and ate hippie (hepevirus) California (calicivirus) pickles (picornavirus).”
        • retrovirus
        • togavirus
        • flavivirus
        • coronavirus
        • hepevirus
        • calicivirus
18
Q

naked viral genome infectivity

A
  • purified nucleic acids of most dsDNA (except poxviruses and HBV) and + strand ssRNA (= mRNA) viruses are infectious.
  • naked nucleic acids of - strand ssRNA and dsRNA viruses are not infectious
    • they require polymerases contained in the complete virus
19
Q

DNA viruses–viral replication

A
  • all replicate in the nucleus
    • except poxvirus
20
Q

RNA viruses–viral replication

A
  • all replicate in the cytoplasm
    • except influenza virus and retroviruses
21
Q

name the naked (nonenveloped) viruses

A
  • Papillomavirus
  • Adenovirus
  • Parvovirus
  • Polyomavirus
  • Calicivirus
  • Picornavirus
  • Reovirus
  • Hepevirus
    • “Give PAPP smears and CPR to a naked hippie”
22
Q

which of the naked (nonenveloped) viruses are DNA?

A
  • PAPP
    • ​Papillomavirus
    • Adenovirus
    • Parvovirus
    • Polyomavirus
23
Q

which of the naked (nonenveloped) viruses are RNA?

A
  • CPR and hip
    • ​Calicivirus
    • Picornavirus
    • Reovirus
    • hepevirus

USMLE Step I Microbiology (44 decks)

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