INF2 - E. VIRUSES-COVERED Flashcards

1
Q

what are viruses

A

small, sub cellular organisms with an obligate intracellular lifestyle ie - need to live in our cells to replicate

between living and non-living

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2
Q

what size are viruses

A

20-100 nm
smaller than bacteria and animal cells

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3
Q

where are viruses found

A

ubiquitous
each of us is infected with at least 2 different viruses ie - HSV-1 or 2
viral infections are persistent (ie always infected as they incorporate their genome into our DNA)

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4
Q

properties of viruses

A
  1. DNA or RNA packaged into particles for transmission between hosts
  2. viral genome contains info needed for replication within a permissive host cell
  3. viral survival ensured by establishing its genome in a host cell
  4. obligate intracellular parasites: need the cellular machinery to replicate themselves
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5
Q

what are the 2 ways viruses can be classified by

A
  1. absence/presence of an envelope (envelope or naked)
  2. shape of capsid (protein) - helical or icosahedral (20 sided)
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6
Q

why icosahedral shape

A
  • nearest geometrical shape to a sphere
  • highest volume/surface ratio (ie lots can be packed without using too much protein)
  • only one gene needed: multiple repetitions of single protein
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7
Q

how do viral capsids self-assemble

A
  • each subunit has identical bonding contacts with its neighbouring proteins (ie easily bonds)
    achieved by symmetrical assemblies of oligomers
  • proteins linked by non-covalent bonds so rapid assembly and disassembly
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8
Q

what is the function of the capsid

A
  1. protection for nucleic acid outside cell
    - capsid made from multiple subunits, not covalently linked
    - symmetry provides maximal contact points
    - capsid is metastable: unfolds in cells as conditions like pH change
  2. provides specific attachment to cell receptors (for naked)
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9
Q

differences between naked and enveloped regarding transmission

A
  • enveloped are sensitive to dryness, heat, detergents, acids
  • must stay wet to be transmitted (air droplets, warm air breathe in), don’t typically survive in GI tract eg - HIV1
  • naked are resistant to dryness, heat, detergents, acids, proteases
  • can remain infective upon drying, on fomites, survive in GIT and surfaces eg - Adenovirus
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10
Q

key terms

A
  • capsid: protein shell containing viral genome
  • nucleocapsid: capsid containing nucleic acid
  • capsomer: individual protein molecules which form capsid
  • envelope: lipid bilayer derived from host cells around capsid
  • tegument: additional protein layer located between capsid and envelope
  • virion: complete, infective viral particle outside the cell
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11
Q

attachment of viruses

A
  • bind to specific receptors on host cells
    HIV1 to CD4 and CXCR4 (co-receptor) on T-cells
    influenza virus to sialic acid on respiratory epithelium
  • specific cell type/tissues = tropism
  • specific host range: ability of virus to infect different species
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12
Q

uncoating of viruses

A
  • fusion of viral envelope with hosts cells plasma membrane followed by capsid disassembly
  • naked viruses: endocytic uptake through a endosome (vesicle), pH drops in endoscope and clathrin disassembles and virus released
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13
Q

reproduction of viruses

A
  • make new copies RNA/DNA
  • produce viral proteins and enzymes
  • assemble and release new viral particles
  • replicate their nucleic acid, packaged into new capsids, released
  • virus has small number of genes and relies on host cell machinery to replicate
  • begins immediately after viruses have entered host cell and release genetic material
  • eclipse phase: incubation period
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14
Q

assembly and maturation of viruses

A
  • assembled into new virions
  • spontaneous self-assembly process
  • may still be non-infectious so maturation has to occur
  • maturation: proteolytic cleavage by viral or cellular proteases
    ie - HIV gag polyprotein by HIV protease
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15
Q

release of viruses

A
  • budding eg HIV
  • cell bursts open: lytic viruses (cell lysis then occurs of virus) eg - polio virus
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16
Q

how do viruses cause cellular damage

A

direct damage to infected cells: cytopathic effects

  1. cell lysis: cells burst open to release new virions
  2. cell fusion: several cells fused as viruses move from one to another - multi-nucleated syncytia
  3. transformation: DNA or RNA tumour viruses may medicate multiple changes that convert a normal cell into a malignant one (oncogenic viruses)
  4. DNA damage: breakage, fragmentation, rearrangement and changes in no of chromosomes may occur of our own cells (genotoxic effects - mutations - cancer)