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DWT > Virology 3: Viral Replication > Flashcards

Virology 3: Viral Replication Flashcards

1
Q

What is a Virion

A

The complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid.

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2
Q

Viral replication cycle in host cell steps

A
  1. Attachment
  2. Penetration
  3. uncoating
  4. Transcription of early mRNA
  5. Translation of early proteins
  6. Replication of viral DNA
  7. Transcription of Late DNA
  8. Translation of late proteins
  9. Assembly of Virions
  10. Release
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3
Q

What is attachment? What mediates this process?

A

Virus recognition of target cells.
Mediated by two molecules:
1. VAPs on surface of virion
2. receptor of target cell

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4
Q

What are VAPs on different types of viruses?

A

Viral attachment protein:
-Non-enveloped: part of capsid or protein extending from capsid
-Enveloped Virus: Spike/ peplomer glycoproteins on the envelope.

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5
Q

What are host cell receptors and what is their significance to the virus?

A

What they are:
- Proteins
- carbohydrates on glycoproteins
- glycolipids on the cell surface.
What their significance is:
- Assist with the virus recognizing the target cell.
-determine host range and tissue tropism

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6
Q

What is tissue tropism?

A

Range of cells and tissues of a host that support growth of a particular pathogen

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7
Q

What is Penetration? What are types of penetration?

A

After attachment: Energy dependent and rapid.
- Enters through 3 mechanisms:
1. Fusion: Enveloped
2. Endocytosis: Enveloped
3. Translocation: Non-enveloped

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8
Q

Fusion penetration

A

Enveloped Viruses
Vesicle the virus is in fuses with cell membrane to release virus inside

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9
Q

Endocytosis penetration

A

Enveloped viruses
Wraps virus in a vesicle made from cell membrane. Usually combines with lysosome to destroy cell.

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10
Q

Translocation penetration

A

Non-enveloped virus
Simply passes through

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11
Q

What happens during uncoating?

A
  • Nucleocapsid is disintegrates
  • genome is freed in cytoplasm
  • proteins are disintegrated in cytoplasm
  • Synthesis of viral proteins by cellular metabolism can occur
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12
Q

What happens during translation or viral proteins?

A

-Viral genome is translated into viral protein using host cell mechanics.

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13
Q

What are the steps of Macromolecular Synthesis?

A

transcription, translation, post-translational modification, and viral genome replication

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14
Q

What are post-translation modifications to mature a viral protein?

A
  • Phosphorylation (nucleic acid binding)
    -Fatty Acid acylation (membrane insertion)
  • Glycosylation
  • Proteolytic cleavage
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15
Q

Where does macromolecular synthesis occur for DNA viruses?

A

-Nucleus
- Use host cell RNA polymerase II and other enzymes to transcribe viral mRNA

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16
Q

Where does macromolecular synthesis occur for RNA viruses?

A

-Cytoplasm
-Virus must encode for enzymes used in transcription and replication in their genomes

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17
Q

What occurs during assembly of virions?

A
  • Viral matrix protein drags viral nucleocapsid toward membrane
  • Brings toward membrane in area fused with viral glycoproteins
  • Combining proteins made with replicated DNA
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18
Q

What occurs during maturation of virion?

A

The cell membrane area with the viral glycoproteins will begin to bud and pinch

*At this point a non-enveloped virus will combine with lysozyme to release

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19
Q

What occurs during release of virion?

A

The cell membrane is pinched to create free infectious virion.
*** The virion took the portion of the cell membrane that it replaced the proteins with viral proteins.

20
Q

Describe the whole viral life cycle

A

See image

21
Q

What is cytopathic effect (CPE)?

A

Morphological changes of infected cells in vitro such as-
-Rounding (shrinking)
- Lysis (cell death)
- Detachment (from mother)
- Syncytia (Cells fusing)
- Inclusion bodies

22
Q

What does viral replication cause in vivo vs in vitro?

A

In vivo: diseases
In vitro: Cytopathic effects (CPE)

23
Q

What causes cytopathic effects (CPE)?

A
  • Direct injury to cell from virus infecting cells
  • Side effect from altered metabolism due to virus infecting other cells in the body
24
Q

What are the effects of viruses on cellular metabolism?

A

Inhibition of:
1. Cellular transcription mechanisms
2. RNA processing pathways
3. Cellular translation
4. Host cell DNA synthesis
pretty much the virus is using all this machinery

25
Q

What are the effects of viruses on cell structures?

A
  1. Membrane fusion of neighboring cells
  2. Changing the permeability of cell plasma membrane
  3. Disruption of cytoskeletal fiber systems, microfilaments, and microtubules
  4. Cytoskeletal components incorporated into infected cell structures.
26
Q

What does membrane fusion of neighboring cells lead to?

A

Syncytia- many nuclei
- Common characteristic of CPE for several enveloped viruses

27
Q

What does changing the permeability of cell plasma membrane lead to?

A

Increased influx of various ion/toxins causing cell lysis.

28
Q

What does disruption of cytoskeletal fiber systems, microfilaments, and microtubules lead to?

A

Rounding/shrinking of cells.
- Common characteristic of CPE

29
Q

What does Cytoskeletal components incorporated into infected cell structures lead to?

A

Inclusion bodies either in the cytoplasm or nucleus.

30
Q

What type of virus forms inclusion body in the cytoplasm?

A

RNA virus

31
Q

What type of virus forms inclusion body in the nucleus?

A

DNA virus

32
Q

What is an inclusion body

A

Unique structures generated by viral proteins together with some cellular proteins as a platform for efficient viral replication

33
Q

Ways for virus to enter host

A

Respiratory tract
GI tract
Conjuctiva
Genitourinary tract
Skin (epidermis)

34
Q

Viral replication must occur in what kind of cells?

A

Living

35
Q

Characteristics of viral entry through skin

A
  • Barrier: Epidermis, outer keratinized layer of dead cells - virus cant enter
  • Penetration/loss of barrier (cut, bite) - virus can enter
  • Local infection can spread to systemic infection
36
Q

Characteristics of viral entry through respiratory tract

A

AEROSOLS
- Barriers: mucus, mucocillia, WBCs, IgA, Cell mediated immunity
- Factors: droplet size, air currents, humidity, temperature (cold)

37
Q

Characteristics of viral entry through GI tract

A
  • Barriers: Low pH (acidic), proteases, bile salts, mucus, igA, cell-mediated immunity
  • Factors: in some cases GI enzymes enhance viral infectivity
38
Q

What type of virus can survive the stomach acidity?

A

Non-enveloped

39
Q

Characteristics of viral entry through genitourinary tract

A

Barriers: mucus, IgA, cell-mediated immunity

40
Q

Characteristics of viral entry through conjuctiva

A

Barriers: tears containing IgA and IgG
** Not a major route of transmission

41
Q

Infections of the skin will lead to

A

only local infection cell-to-cell spread. Can not penetrate skin barrier

42
Q

What is systemic infection and what are the types?

A

Spread of infection to distant tissues through
1. Hematogenous
2. lymphatic
3. Neural

43
Q

What is a viremia?

A

Virus circulating in the blood
High viremia = virulence

44
Q

Hematogenous spread-
Where does it enter?
Where does it go?
Is it effective?

A
  • Enters through a epithelial surface where replication is limited
  • Primary viremia (small amount of virus) moves to Vascular system (major pathways leading to systemic spread)
  • Primary viremia reaches distant organs (major replication sites)
  • Secondary viremia (large amount) enters vascular system leading to major clinical signs
    *Very effective
45
Q

Lymphatic spread-
Where does it enter?
Where does it go?
Is it effective?

A
  • Enters through epithelial cells, vascular system.
  • Replicates in local aqueous site
  • Spreads through draining lymph to other tissues
    *Ineffective
46
Q

Neural spread-
Where does it enter?
Where does it go?
What is the speed?

A
  • Enters from viremia infections
  • Infectivity dependent on nerve tissue exposure
  • Transport speed: 2-16 mm/day along the nerve axons

DWT (28 decks)

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