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VIROLOGY > 1+2 – Introduction to Viruses and Classification > Flashcards

1+2 – Introduction to Viruses and Classification Flashcards

1
Q

Viruses are everywhere

A
  • Most abundant entities in biosphere
  • Biomass of bacteriophage 1000 fold greater than Earth’s elephant
  • Whales are commonly infected with Calicivirus
  • *sequence more and more=1445 new RNA viruses
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2
Q

Viruses in us

A
  • 8% of our genome from old viral infections
    o Integrated into our germline and are PASSED on to offspring
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3
Q

What is a Virome?

A
  • Total collection of viruses in and on the body
  • May infect both host cells or other microbes (Ex. bacteria)
  • May causes disease or be asymptomatic (due to our immune system)
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4
Q

Archeovirology

A
  • JC virus is ubiquitous humans polyoma virus
    o Use it to track where people came from
    o Two migration model
     JCV and human genes
     JCV but undatable with human genes
  • Humans are only primates known to have more than one Simplexvirus (HSV1 and HSV2)
    o Suggest it was from a cross species event?
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5
Q

Not all viruses are bad

A
  • Many biogeochemical cycles
  • Ex. parasitoid wasps
  • Ex. blooms
  • Ex. grass in Yellowstone National Park
  • Ex. tulips with stripped pattern
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6
Q

Parasitoid wasps

A
  • Viruses encoded in wasp genome are injected with the wasp egg into the insect larva
  • viruses reproduce in larva and reduce immune response to facilitate parasitism
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7
Q

Viruses and blooms

A
  • marine lytic viruses control phytoplankton blooms
  • contribute to bloom development by structuring plankton communities
  • affect nutrient and organic matter fluxes during bloom events
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8
Q

Viruses and the grass in Yellowstone national park

A
  • requires a fungus to survive
  • fungus thermal tolerance requires the Curvularia thermal tolerance virus (CThTV)
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9
Q

Viruses and tulips with stripping pattern

A
  • stripes were caused by infection caused by tulip breaking virus
    o interferes with pigment synthesis
  • *highly coveted tulips
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10
Q

What is a virus?

A
  • ‘poison’ or ‘toxin’
  • *small infectious agents
  • Obligate intracellular parasites
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11
Q

Viruses are obligate intracellular parasites

A
  • Require host metabolic processes to replicate
  • Viral disease is a consequence of this replication OR host’s response
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12
Q

Viruses do NOT

A
  • Carry out metabolic processes
  • Make ATP
  • Cannot INDEPENDENTLY synthesize proteins
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13
Q

What is the largest discovered virus so far?

A
  • Pithovirus
  • ‘zombie’: found in permafrost 30m deep from coastal tundra near East Siberia Sea
  • > 30,000 years old
  • *can survive in permafrost for very long periods
  • Visible by light microscopy
  • Infects amoebae
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14
Q

Virus replication is unique

A
  • Eclipse phase: Take over host cell and use cellular molecular machinery to make parts necessary to assemble PROGENY VIRIONS
  • Assembly and many progeny released from a single cell (‘burst’)
  • Progeny form by de-novo self-assembly from the newly synthesized components
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15
Q

What is the basic anatomy of a virus?

A
  • Protective protein coat (capsid)
  • Genetic material (RNA/DNA)
  • Proteins (enzymes)
  • SOME have ADDITIONAL
    o Lipid envelope
    o Proteins for cell binding or entry (glycoproteins)
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16
Q

What are the 2 main classification systems?

A
  • International committee on the nomenclature of viruses (ICTV)
  • Baltimore system
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17
Q

ICTV classification system

A
  • Grouped according to their shared properties
    o 1. Nature of virion nucleic acid
    o 2. Capsid (protein shell) symmetry
    o 3. Presence/absence of envelope
    o 4. Virion and capsid dimensions
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18
Q

Viral genomes are very variable and can be

A
  • DNA or RNA
  • Have covalently attached proteins or not
  • DNA with short RNA segments
  • Single stranded: +, - or ambisence strand
  • Double stranded
  • Linear
  • Circular
  • Segmented
  • Gapped
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19
Q

Distinct viruses defined by classical taxonomic methods are organized into 7 groups based on structure of their genome

A
  • Viral genome=blue print to make progeny virions
  • *important characteristic for classification
  • Virus families are commonly put in groups accord to their GENOME TYPES
    o All genome types are represented in viruses that infect vertebrates
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20
Q

Baltimore system

A
  • Complements genome structures to classify viruses based on their formation of mRNA
  • *reflects the essential role of host cell translational machinery
21
Q

mRNA synthesis

A
  • All viruses have to produce mRNA that can be translated by cellular ribosomes= (+)mRNA
22
Q

(+)mRNA

A
  • Contains IMMEDIATELY translatable information
  • *goal for virus takeover of the ribosome
23
Q

What are the DNA and RNA complements of the (+) strand designated as?

A
  • (-) strands
24
Q

What are viral particles?

A
  • Protect the genome
  • Designed for effective genome transmission from 1 host cell to another
25
Q

How are genomes protected?

A
  • Within a protein coat (capsid)
    o Sturdy barrier formed by extensive interactions among proteins that comprise the coat
26
Q

Many particles can survive exposure to

A
  • Variable temperatures
  • UV light
  • Desiccation
  • pH
  • chemicals within the environment
  • proteolytic enzymes
  • etc.
27
Q

Some capsids are contained with an envelope. Where are they derived from and what do they contain?

A
  • Derived from cellular membranes
  • Contain viral glycoproteins
28
Q

What does virion infectivity relate to?

A
  • The properties (stability) of the particle
29
Q

What kind of symmetry do rod-like viruses have?

A
  • Helical
30
Q

Helical symmetry is described as

A
  • The number of structural units per helix turn
  • Axial rise per unit
  • Pitch of helix
  • *any volume can be enclosed by varying the length of the helix (an ‘open’ structure)
31
Q

What is the helical protein built from?

A
  • Single protein that folds into an extended structure (‘Dutch clog’)
  • Coat protein subunits interact to form disks
    o Disk assemble in a long, rod-like, right-handed helix
  • Coat proteins each bind 2 nucleotides of RNA genome
  • *a large stable structure formed form multiple copies of a SINGLE PROTEIN
32
Q

What packages the (-) RNA genome in a left-handed helix?

A
  • N protein packages
33
Q

What do N-rings contain?

A
  • Increasing numbers of N molecules from the tip to bas
    o Via different N-N interactions induced by RNA association
34
Q

What stabilizes a N-helix?

A
  • Associated M-helix
  • N-helix turns do NOT closely associate= in ABSENCE of M, nucleoprotein UNWINDS
35
Q

What do all vertebrate viruses with helical symmetry have?

A
  • Envelope
36
Q

What kind of symmetry do spherical viruses have?

A
  • Icosahedral
    o Achieved through various ways
37
Q

Icosahedral capsid

A
  • 60 identical subunits (3/face, 20 faces!) MINIMUM
    o All subunits interact with neighbours in EQUIVALENT MANNER
  • *fixed internal volume (a ‘closed’ structure)
38
Q

What does the number of subunits in a icosahedral capsid determine?

A
  • Capsid size
    o More subunits=larger capsid
  • *most animal viruses are more than 60 capsid subunits and can hold LARGE GENOMES
39
Q

What is T (triangulation)?

A
  • Description of structure in terms of subdivision into smaller triangles
  • 60T=total number of subunits
40
Q
A
41
Q
A
42
Q

What are envelopes?

A
  • Membrane derived from host cell that contains viral proteins
43
Q

What might envelopes differ in?

A
  • Lipid composition: derived from different cellular membranes
  • Number of proteins they contain: many are glycoproteins
  • Location: some bacteriophages have a membrane WITHIN the capsid
44
Q

Viral glycoproteins are integral membrane proteins, what are their 2 domains?

A
  • External domain
  • Internal domain
45
Q

External domain (viral glycoproteins)

A
  • Decorated with oligosaccharides
  • Contain binding sites for cell surface receptors
  • Contain major antigenic determinants
  • Have sequences to mediate fusion with cellular membranes
46
Q

Internal domain (viral glycoprotein)

A
  • Makes contact with other virion components
  • Typically essential for virus assembly
47
Q

What are some non-structural proteins that are important for establishing an efficient infectious cycle?

A
  • Enzymes necessary to synthesize viral nucleic acids
  • Enzymes to modify viral RNA transcripts (vaccinia virus)
  • Other enzymes
    o Integrase
    o Proteases
    o Protein kinases
    o RNases
48
Q

Examples of enzymes necessary to synthesize viral nucleic acids

A
  • mRNA from an RNA template
  • viral DNA from an RNA template
  • DNA-dependent RNA polymerase

VIROLOGY (12 decks)

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