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Microbiology > L22: Intro to Medical Virology > Flashcards

L22: Intro to Medical Virology Flashcards

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Biology 101 flashcards
1
Q

Characteristics of a virus

A

Acellular infectious agent with nucleic acid surrounded by protein coat; obligate parasite; 20-300 nm

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2
Q

Virion components

A

Simplest viruses just have capsid and genome, more complex have envelope (lipid layer with special proteins) with matrix between; genome can either be DNA or RNA

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3
Q

Segmented vs. contiguous viral genomes

A

Segmented need ALL of DNA to have complete genome

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4
Q

Types of viral genomes

A

ssDNA, dsDNA, ssRNA (- or + sense), dsRNA

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5
Q

(+)ssRNA

A

In correct orientation to direct cell synthesis; can generate template for ribosome

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6
Q

(-)ssRNA

A

In opposite orientation (inert in cells); use RNA as template

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7
Q

Properties of RNA viruses

A

CELLS CANNOT REPLICATE RNA –> need RNA polymerase; labile and transient, replicate in cytoplasm, must carry polymerases (except +RNA genome), prone to mutation

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8
Q

Capsid structures

A
  • -Helical (slinky)
  • -Icosahedral (regular, closed)
  • -Complex (variation of icosahedral)
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9
Q

Naked capsid viruses

A

Environmentally stable to temperature, acid, proteases, detergents, drying; released by lysis; spread easy, retain infectivity even when dry

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10
Q

Envelope viruses

A

Environmentally labile, disrupted by acid, detergents, drying, heat; modifies cell membrane during replication and are released by budding; must stay wet (can’t survive GI tract), spread in droplets, don’t need to kill cell to spread

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11
Q

Virus life cycle

A
  1. Attachment
  2. Entry
  3. mRNA production
  4. Protein and genome synthesis
  5. Virion assembly
  6. Egress
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12
Q

Attachment

A

Attachment to membrane occurs with cell receptors, fusion to membrane, allowing capsid to enter (Ex. HIV)

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13
Q

Entry

A

Receptor engagement with viral proteins that leads to an enveloped virus, pH triggers degradation of envelope and capsid is released

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14
Q

How do cells produce mRNA (dependent on genome)?

A

dsDNA: can just use transcriptional machinery
ssDNA: use cellular DNA repair enzymes to produce dsDNA
+ssRNA: retroviruses use viral reverse transcriptase to make dsDNA, others use genome just like mRNA molecule
-ssRNA: use viral RdRp to make mRNA
dsRNA: use viral RdRp to make mRNA

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15
Q

How can cellular DNA replication machinery be made available at all times for DNA viruses?

A
  • -Papovaviruses stimulate cell growth and synthesis to have cell make them
  • -Poxviruses encode polymerase and enzymes
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16
Q

How can RNA viruses make cellular RdRp?

A

+ssRNA: encode RdRp then make enzymes

-ssRNA: encode RdRp and enzymes right away

17
Q

Viral assembly

A
  1. Individual viral proteins form into capsid subunits, which combine to form complete capsid
  2. Viral genome and components are selectively packaged in capsid
  3. Virus exits cell
18
Q

Budding (to leave cell)

A

Viral envelope proteins forming a patch on membrane, recruiting integument proteins, protruding, then releasing into extracellular environment

19
Q

Viral genetics

A

Can change through:

  • -Point mutations (slow)
  • -Recombination (DNA viruses)
  • -Reassortment (ex. influenza, two segments affect cell and reassort inside cells to lead to quick, large change)
20
Q

Viral infection types

A
  • -Acute
  • -Chronic
  • -Latent
21
Q

Acute infection

A

Affected by virus, immune system kicks in and virus is eradicated

22
Q

Chronic infection

A

Continuous lower level of virus but never disappears totally (6 months or more)

23
Q

Latent infection

A

Looks like acute but can reactivate (cycle can continue for long time)

24
Q

Invasion of viruses into body

A

Can occur through oral transmission, droplet transmission, direct inoculation, direct skin contact, sexual transmission, or transplacental

25
Q

Cytopathic effect

A

Injury to a tissue by a virus; utilized in plaque assay

26
Q

Plaque assay/virus culture (viral diagnostics)

A

Detects infectious virus, positivity shows active viral infection, restricted to viruses that replicate in tissue

27
Q

Electron microscopy (viral diagnostics)

A

Detects virion particles, especially helpful in identification of emerging viruses, relatively expensive and challenging

28
Q

Antigen detection, ex. ELISA (viral diagnostics)

A

Detects viral proteins and glycoproteins, sensitive and quick but requires specific antibody

29
Q

PCR (viral diagnostics)

A

Detects DNA genomes, highly sensitive but DNA sequence must be available

30
Q

RT-PCR (viral diagnostics)

A

Detects RNA genomes, highly sensitive but RNA sequence must be available

31
Q

Serology, ex. Western blot (viral diagnostics)

A

Detects anti-viral antibodies, sensitive and quick but takes time and care

Microbiology (20 decks)

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