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Virology > Lecture 4 - Virus Replication Cycle > Flashcards

Lecture 4 - Virus Replication Cycle Flashcards

1
Q

What is a resistant cell?

A

No receptor and cannot be naturally infected by that virus

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2
Q

What is a permissive cell?

A

Susceptible to infection (has a suitable receptor for the virus to attach to) and the capacity to support the full virus replication cycle

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3
Q

What is a semi-permissive cell?

A

Susceptible to infection but does not support the full virus replication cycle

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4
Q

What is a susceptible cell?

A

Has a functional receptor for the virus to bind to and may or may not be able to support the full virus replication cycle

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5
Q

What is virus tropism?

A

Ability of a virus to infect a specific host or a specific type of host cell

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6
Q

What is the multiplicity of infection (MOI) and what does it vary between?

A
  • Average number of infectious virus particles per cell

- Varies between cell types (cell types differ in permissiveness)

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7
Q

What does an MOI = 1 indicate?

A

Using a Poisson random distribution curve, MOI=1 indicates that 1/3 of cells will receive one hit (1 virus), 1/3 of cells will receive more than one hit (>1 virus) and 1/3 of cells will receive less than one hit. This means that about 33% of cells will not get infected at this MOI

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8
Q

What MOI is required for complete, synchronous infection of the cell monolayer (>99% of cells get infected)

A

MOI > 5

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9
Q

What is the procedure for obtaining a virus growth curve

A
  • Using MOI = 5-10, apply viruses at 4 degrees C (allows for attachment but not entry to synchronise infection)
  • Change temperature to 37 degress
  • Harvest extracellular supernatant and virus-infected cells at specific time points over hours or days and titre virus in each fraction
  • Compare and contrast eclipse and latent phase for enveloped and naked viruses
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10
Q

What 2 things are required for virus attachment to a host cell?

A

Viral-attachment protein (VAP) and a specific cell receptor

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11
Q

What occurs during virus penetration?

A

The virus crosses a cell or endosomal membrane

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12
Q

What is the difference in uncoating location for RNA and DNA viruses

A

RNA viruses uncoat in the cytoplasm

DNA viruses uncoat in the nucleus

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13
Q

What 2 ESSENTIAL steps need to occur for successful virus uncoating?

A
  • The stable virus capsid structure needs to be destabilized (metastability)
  • Uncoating needs to deliver the virus genome in a replication-competent format to the correct subcellular compartment
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14
Q

What is required for a genome to be in a replication competent format?

A

Nucleic acid plus any essential proteins

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15
Q

What is the correct subcellular compartment an RNA virus genome needs to be delivered to?

A

Cytoplasm

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16
Q

What is the correct subcellular compartment a DNA virus genome need to be delivered to?

A

Nucleus

17
Q

What 2 types of release from the host cell may occur for viruses?

A

Budding or lysis

18
Q

What are the 3 steps in virus entry and what is the function of entry?

A

Attachment, penetration and uncoating

Delivery of replication competent form of genome to the correct subcellular compartment

19
Q

What are the 3 steps of viral macromolecular synthesis?

A

Transcription, translation and genome replication

20
Q

Does viral MMS occur simultaneously or in discrete steps?

A

Simultaneously

21
Q

What are 2 types of control for viral MMS?

A

Cis factors and trans factors

22
Q

What are the 2 steps in virus maturation?

A

assembly and release

23
Q

What property of viruses are entry and maturation dependent on?

A

Whether the virus is naked or enveloped

24
Q

What is an abortive virus cell infection and what causes it? What permissiveness would these cells have?

A

No infectious virus progeny are produced because the virus replication cycle is stalled before maturation
Often due to lack of host cell factor required for virus replication
Semi-permissive cells

25
Q

What is a productive virus cell infection and what does it look like?

A

Production and release of infectious progeny virions

Often CPE are observed

26
Q

What is a latent virus cell infection?

A

Persistence of viral genome in host cells with no detectable virus production, often subject to reactivation

27
Q

What is a persistent virus cell infection? Is it lytic or non-lytic? Would you expect to observe cytopathic effects in a persistent infection?

A

Productive, long-term infection generating infectious progeny virions.
Non-lytic infection
Frequently CPE are absent

28
Q

What is a transforming virus cell infection and what can it cause? What is the permissivity of these cells?

A

Little or no virus production, altered cell growth and morphology that may lead to cancer.

29
Q

What are the characteristics of an acute viral infection?

A

Usually rapid and self-limiting (or cleared by host response) but can be fatal

30
Q

What is an oncogenic virus?

A

Viruses that induce cell transfomation and cancer

31
Q

What are 3 examples of intrinsic host defenses to viruses and what they do

A
  • Autophagy disrupts intracellular virus replication
  • Apoptosis kills virally infected cells
  • microRNAs inhibit virus replication
32
Q

What are 3 examples of innate host defense mechanisms?

A
  • Complement
  • Natural killer cells
  • Antigen presenting cells
33
Q

What are 3 ways host cells can sensethe presence of a virus?

A
  • virus binding and activation of host cell receptors
  • activation of nucleic acid receptors on endosomes (TLR)
  • nucleic acid-binding proteins in the cytoplasm (RIG-1, PKR)
34
Q

What is the result of activating virus-sensor pathways?

A

Lead to production and release of soluble immune mediators (cytokines, chemokines) which recruit and activate specific adaptive immune responses

Virology (14 decks)

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