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Foundations III > virus structure and life cycle > Flashcards

virus structure and life cycle Flashcards

1
Q

by what characteristics are viruses classified?`

A
  • type/structure of nucleic acid
  • type/symmetry of virus capsid
  • envelope (+/-)
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2
Q

virion

A

complete viral particle = nucleic acid + capsid

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3
Q

capsid

A
  • protective protein coat formed by self-assembly of identical protein subunits (capsomeres) encoded by viral genome
  • only a few proteins
  • shape is helical or icosahedral
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4
Q

capsomeres

A

protein subunits of viral capsid

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5
Q

envelope

A
  • outer covering of virus made of lipid bilayer and glycoproteins derived from the host cell membrane (outer membrane or inner membranes such as nuclear or ER)
  • may help viruses avoid immune response
  • help viruses bind and enter host cell
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6
Q

compare the characteristics of enveloped vs non-enveloped viruses

A

enveloped:

  • sensitive to dessication in the environment
  • transmitted via respiratory, parenteral, and sexual routes

non-enveloped:

  • stable to harsh environmental conditions
  • transmitted by fecal-oral route (survive well in water) and from surfaces
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7
Q

elements of viral structure

A
  • genome
  • nucleoproteins = proteins associated with nucleic acid
  • nucleocapsid = association of viral capsid proteins with viral nucleic acid
  • matrix/tegument = structural proteins linking envelope with virus core
  • envelope
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8
Q

adenovirus shape

A

icosahedral

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9
Q

orthomyxovirus shape

A

helical

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10
Q

picornavirus shape

A

icosahedral

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11
Q

hepadnavirus shape

A

helical (spheres and filaments)

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12
Q

poxvirus shape

A

brick

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13
Q

retrovirus shape

A

icosahedral

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14
Q

characteristics of RNA genomes

A
  • smaller size
  • higher error rate
  • max size limit
  • often exist as quasispecies
  • may exist as segmented genomes
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15
Q

benefits of segmented genomes

A
  • reduce the chance that an error will incapacitate the whole genome
  • reassortment => evolutionary advantage
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16
Q

characteristics of DNA genomes

A
  • larger size

- high fidelity replication and proofreading ability (except ssDNA)

17
Q

what are the stages of productive viral infection?

A
  1. attachment via host cell type specific glycoproteins on the viral surface; enveloped viruses fuse viral envelope with cell membrane
  2. penetration
  3. uncoating and disassembly
  4. take over host functions for: transcription and translation
  5. replication
  6. self assembly
  7. release (usually via cell lysis)
18
Q

cell susceptibility vs resistance (with respect to viruses)

A

susceptible = express receptors needed for viral entry

resistant = lack receptors for viral entry

19
Q

ss(+)RNA virus life cycle

A
  • ss(+)RNA = mRNA => enters the host cell “translation competent” and translation occurs immediately using host cell cytoplasmic ribosomes
  • synthesized polyprotein must be cleaved by viral protease into active protein subunits
  • must make a (-)RNA to serve as template for genome replication
20
Q

ss(-)RNA virus life cycle

A
  • requires viral enzyme (RNA-dependent RNA polymerase) to make mRNA and genomic ss(+)RNA from the ss(-)RNA
  • occurs in the cytoplasm
21
Q

DNA viruses

A
  • replicate in nucleus (except poxviruses, which bring their own replication machinery)
  • transcription begins with early mRNA (regulatory proteins and DNA replication machinery needed to take over host cell) then late mRNA (structural proteins)
22
Q

retrovirus life cycle

A
  • viral RNA dependent DNA polymerase (reverse transcriptase) makes dsDNA from ss(+)RNA
  • viral dsDNA integrated into the host cell chromosome (provirus)
  • transcription thus regulated by host cell
23
Q

forms of viral infection

A

non-permissive = cells lack receptors for viral entry

productive = new infectious virus produced

abortive = no new infectious virus produced

latent = no immediate virus production but potential for later virus production

24
Q

consequences of viral infection for host cell

A
  • cellular processes compromised
  • may induce apoptosis (some viruses block it though)
  • usually will end in cell death via cytotoxic effects of viral products or host immune response
25
Q

clinical consequences of viral infection

A
  • inapparent infection
  • illness due to infection (rapid multiplication and lots of cell death)
  • illness due to persistent infection (chronic tissue damage)
  • cancer (cells transmformed)
26
Q

genetic bases of latent viral infections

A
  • episomal = plasmid

- proviral = integrated into host cell chromosome

27
Q

general characteristics of DNA viruses

A
  • dsDNA (not parvovirus)
  • linear (not HPV, HBV, polyomavirus)
  • isocahedral (not poxvirus)
  • nuclear replication (not poxvirus)
28
Q

general characteristics of RNA viruses

A
  • ssRNA (not reovirus, orthomyxovirus)
  • replicate in cytoplasm (not influenza, retroviruses)
  • haploid (not retroviruses)

Foundations III (26 decks)

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