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IAHI Block 3 > 1 - Intro to Virology > Flashcards

1 - Intro to Virology Flashcards

1
Q

Viruses are obligate intracellular parasites, what does this mean?

A

They rely on host metabolic machinery and protein biosynthetic machinery.

“autonomy” from host cell enzymes varies widely among viruses.

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2
Q

Describe the virion size, structure, and genome?

A

Diameter from ~300 nm to ~20 nm and are filtrable agents best viewed by electron microscopy.

Can be enveloped with membrane or naked.

Genome can be DNA or RNA.

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3
Q

Describe the intracellular and extracellular phase that a virus goes through?

A

Intra: transcription, replication, synthesis of new proteins, assembly of virions within infected cell.

Extra: particles must pass from cell to cell or throughout body, between individuals, or between individuals and insect vectors.

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4
Q

What is the size of a virus compared to a cell?

A

100 to 1000x smaller than a cell.

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5
Q

The taxonomic method used in virology is ______? What does this mean?

A

Polythetic:

  • any virus is described using a collection of individual properties
  • members always have several but not all properties in common
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6
Q

What is the polythetic taxonomic method important for?

A 
Diagnosis 
Identification of new viruses
Clarification of life cycle 
Drug use and design 
Vaccine development
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7
Q

What are the five properties used for classification?

A
  1. Particle type: icosahedral, filamentous, irregular proteins capsid. Membrane enveloped or naked.
  2. Genome type:
    ~RNA: + sense (mRNA), - sense ds, segmented.
    ~DNA: ss, ds, linear, circular
  3. Tissue tropism
  4. Disease etiology
  5. Serology
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8
Q

Describe the different particle types that viruses may have? What function does this serve?

A

Capsids from one or more proteins w/ repeating protein-protein contacts.

Capsids can form naked viruses or be surrounded by a membrane for enveloped viruses (matrix protein lies under envelope)

Capsid/envelope are the delivery vehicle during transmission.

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9
Q

What are two examples of viruses that are icosahedral and non-enveloped?

A

Adenovirus and papillomavirus (dsDNA)

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10
Q

What are examples of an icosahedral enveloped viruses and a helical enveloped virus?

A

Icosahedral/enveloped: Herpes simplex virus

Helical/enveloped: paramyxovirus

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11
Q

What is the major difference between having a naked and enveloped virus?

A

Exposed proteins on the capsid and membrane are targets of neutralizing antibodies.

Naked are more stable and can last longer on surfaces than enveloped viruses can because lipid envelopes break down.

Antibodies against viral antigens are used in serology assays for diagnosis.

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12
Q

For viral genome typing, what is the Baltimore classification? Describe types I-IV

A

Classification provides initial understanding of how a given virus will replicate

I: dsDNA
II: ssDNA
III:dsRNA 
IV and V: ssRNA
 - IV is positive sense 
 - V is negative sense
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13
Q

Icosahedral RNA viruses can be ____ or _____, while helical RNA viruses are all ______.

A

Icosahedral can be naked or enveloped.

Helical are all enveloped.

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14
Q

For DNA viruses, describe the structure of icosahedral, helical, and complex viruses?

A

Icosahedral can be naked, enveloped, or naked/enveloped (cytoplasmic)

Helical are all enveloped.

Complex are all enveloped (cytoplasmic).

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15
Q

What is a virion? What is a virus? What is viremia? How are viruses visualized?

A

Virion: a viral particle
Virus: an infectious particle
Viremia: spread of virus throughout the body via the bloodstream

Seen via electron microscopy.

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16
Q

What is MOI? What is CPE? What is infectivity?

A

MOI: multiplicity of infection (virus/cell)

CPE: cytopathic effect, structural changes in host cell caused by viral invasion

Infectivity: infectious particles / non-infectious particles

17
Q

How are viral infections quantified?

A

Plaque assay: titration of # of infectious progeny per volume (plaque forming units)

Focus forming assay: for viruses promoting cell proliferation rather than death

Single-step growth curve: provides quantitation of ‘burst size” (put one particle in and determine how much virus is coming out of that system).

18
Q

What are tissue culture models of infection?

A 
Cytopathic effect 
Cytolytic effect
Transforming (oncogenic effect) 
Induction/production/release of diagnostic enzymes 
Expression of diagnostic antigens
19
Q

What do naked capsid viruses contain? What do enveloped viruses contain?

A

Naked capsid: DNA or RNA + structural proteins +_ enzymes and nucleic acid binding proteins = nucleocapsid

Enveloped: Everything listed above + glycoproteins and membrane

20
Q

What are components of a virion particle? What is the dilemma they’re faced with?

A
  • Genome
  • Enzymes (none or many)
  • Auxillary proteins for assembly, blocking immune response, and disassembly
  • Structural proteins
  • Attachment proteins
  • Fusion proteins
  • membrane

Need a particle that’s stable enough to survive outside the host, but that can be effectively disassembled during the next round of infection.

21
Q

What does a sucessful virus need to be able to do?

A
  1. Initiate infection
  2. Replication/macromolecular synthesis
  3. Virus assembly and egress (release from cells)
  4. Hold host at bay long enough to undergo replication
22
Q

What are the basic steps in a viral life cycle?

A
  1. Recognition
  2. Attachment
  3. Penetration
  4. Uncoating
  5. Transcription
  6. Synthesis of components
  7. Genome replication
  8. Assembly of viral components
  9. Exit/maturation
23
Q

What is involved in virion attachment?

A
  1. Viral surface proteins
    - Both naked and enveloped viruses
    - Recognizes a cell receptor on the target cell
  2. Cell surface receptors
    - Protein or carbohydrate
    - Can determine species, tissue and/or cell tropism
24
Q

What are the components of virion entry?

A
  1. Naked virus: enter cell via endocytosis, and are surrounded by an endosomal membrane.
  2. Enveloped virus: fusion or virus and cell membranes releases capsid into the cytoplasm. Acidification of compartment results in membrane fusion and capsid release.
25
Q

How does transcription and genome replication of viruses occur?

A

Replicative pathway depends on the enzymes that the virus encodes such as DNA polymerases, RNA polymerases, and reverse transcriptase.

Cells do no have enzymes that copy RNA to RNA or RNA to DNA.

26
Q

All viruses must synthesize ________ to make proteins and must use ______ to synthesize viral proteins.

A

All viruses must synthesize + sense mRNA to make proteins.

All viruses must use host ribosomes to synthesize viral proteins, although viral proteins may modify their translational activity.

27
Q

Many viruses “shut off” host _____ synthesis, while others manipulate the ______ ______ of the host to provide the best replicative environment.

A

Many shut off host macromolecular synthesis.

Others manipulate the cell cycle of the host.

28
Q

What are the major components of assembly and morphogenesis?

A
  1. Interplay between viral components and cellular trafficking
  2. Viral membrane proteins must be made
  3. Capsids acquiring a membrane
29
Q

What are the four different outcomes of infection?

A
  1. Productive infection: leads to cytopathic effect with a burst of virus production
  2. Latent infection: no infectious virus particles, but genetic information remains
  3. Abortive infection: virus life cycle incomplete and virus lost
  4. Transforming: immortalizing with/without virus production
30
Q

What factors influence viral spread and tropism?

A
  1. Transmission: respiratory, fecal/oral, direct contact, vectors
  2. Tropism: cellular receptor, tissue-specific receptor, environmental (temp, pH, proteases)
31
Q

What are the mechanisms of pathogenesis (ie how do viruses cause disease)?

A
  1. Destruction of infected cells (lysis)
  2. Modification of infected cell function
  3. Immune and inflammatory responses to virus infection
  4. Combination of several factors
32
Q

What host defenses are used against viruses?

A
  1. Innate response: IFNs, cytokines, chemokines, antiviral response, make surrounding cells resistant to infection.
  2. Adaptive response: humoral - neutralizing antibodies block attachment/entry
    - complement fixing antibody lyse virons or infected cells
  3. Adaptive response: cell-mediated - MHC presentation of viral peptides
  4. Memory response (B and T cells) - resist infection

IAHI Block 3 (18 decks)

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