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2nd year - Microbiology > Virology - Lecture 2 > Flashcards

Virology - Lecture 2 Flashcards

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1
Q

What are four things viruses need to survive?

A

1) Genetic material
- DNA, RNA
2) The ability to replicate
- Genome replication relies on host or viral genes
3) Gene expression
- Trasncription relies on host or viral genes (RNA polymerase)
- Translation relies on host translational machinery (ribosomes)
4) Structural integrity
- Capsid, envelope

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2
Q

What are the seven stages of the life cycle of a virus?

A

1) Binding
2) Entry
3) Uncoating
4) Viral gene expression
5) Genome replication
6) Virus assembly
7) Egress

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3
Q

Describe the first phase of viral life cycle (binding)

A

A viral ligand bind to a cellular receptor.
a host cell or organism is susceptible to infection by a particular virus if the host bears a cognate receptor for the virus

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4
Q

Describe the second phase of viral life cycle (entry)

A

Fusion
Endocytosis
Cell membrane disrutption

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5
Q

Describe the third phase of viral life cycle (uncoating)

A

Virus releases genetic material for gene expression and replication
Mediated by viral or cellular enzymes

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6
Q

Describe the fourth phase of viral life cycle (viral gene expression)

A

mRNA trascription often required
Translation using host ribosomes required
Some viruses encode their own transciptional machinery

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7
Q

Describe the fifth phase of viral life cycle (genome replication)

A

Virus may use host machinery
Some viruses encode viral replication machinery
ALL RNA viruses encode a viral polymerase for replication

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8
Q

Why do all RNA viruses encode viral polymerase for replication?

A

Host cells (humans) do not possess polymerase that turn RNA into DNA. Therefore, RNA viruses must possess an RNA dependent RNA-polymerase to carry out transcriptoin o the negative strand into the positive strand and then it can be translated by the host’s ribosomes into proteins.

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9
Q

Describe the sixth phase of viral life cycle (virus assembly)

A

This phase is spontaneous

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10
Q

Describe the seventh phase of viral life cycle (egress)

A

Lysis

Exocytosis

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11
Q

Describe susceptibility

A

The ability of a virus to bind to a cellular receptor

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12
Q

Describe permissivity

A

the ability of a virus to replicate in a host cell/organism

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13
Q

Describe tropism

A

The range of cell types, tissues or organisms that are both susceptible and permissive to replication
Ex) Rabies virus has tropism for humans and many animals - it is a neurotropic virus

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14
Q

In the Baltimore Classification System of Viruses:

How many classes are there?

A

Seven

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15
Q 
In the Baltimore Classification System of Viruses:
What is class I?
A

dsDNA viruses

  • herpesviruses
  • poxviruses
  • papillomaviruses
  • adenoviruses
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16
Q 
In the Baltimore Classification System of Viruses:
What is class II?
A

ssDNA viruses

  • parvoviruses
  • circoviruses
17
Q 
In the Baltimore Classification System of Viruses:
What is common between class I and II (dsDNA & ssDNA)
A

Most use host DNA-dependent DNA polymerase to replicate genome
Rely on cellular replication machinery
Rely on host transcriptional and translational machinery

18
Q 
In the Baltimore Classification System of Viruses:
What is class III?
A

dsRNA viruses

-reoviruses

19
Q 
In the Baltimore Classification System of Viruses:
What is class IV?
A

(+)ssRNA viruses

  • picornaviruses
  • flaviviruses
20
Q 
In the Baltimore Classification System of Viruses:
What is class V?
A

(-)ssRNA viruses

  • orthomyxoviruses
  • rhabdoviruses
21
Q 
In the Baltimore Classification System of Viruses:
What is common between class III, IV & V ((dsRNA, (+)ssRNA & (-)ssRNA)?
A

These classes must encode an RNA-dependent RNA polymerase in their genome

(-)ssRNA viruses must package an RNA-dependent RNA polymerase in each viral particle

22
Q 
In the Baltimore Classification System of Viruses:
What is class VI?
A

(+)ssRNA viruses with a DNA intermediate

-retroviruses

23
Q 
In the Baltimore Classification System of Viruses:
What are some characteristics of class VI ((+)ssRNA with DNA intermediate)?
A

Require a virally encoded reverse transcriptase in the virus particle
Revers transcrition and viral integration are hallmarks of the retroviral family

24
Q 
In the Baltimore Classification System of Viruses:
What is class VII?
A

dsDNA viruses with an RNA intermediate

-Hepatitis B

25
Q 
In the Baltimore Classification System of Viruses:
What are some characteristics of class VII (dsDNA with RNA intermediate)?
A

Require a virally encoded reverse transcriptase for genome replication
Genomic DNA is transcribed into mRNA for viral gene expression
mRNA is revers transcribed by RT to make genome copies during replication

26
Q

What does a lytic infection result in?

A

Results in host cell lysis

-rhabdoviruses

27
Q

What does a lysogenic infection result in?

A

Results in virus production without cell lysis

-retroviruses, herpesviruses

28
Q

Describe an acute infection

A

Infection characterized by a rapid production of virus and/or rapid onset of disease symptoms, followed by clearance by the host
-rhabdoviruses

29
Q

Describe a persistent infection

A

Infections occur when the primary infection is not clears

-retroviruses, herpesviruses

30
Q

Describe a chronic infection

A

Infections are persistent infections that are eventually cleared

31
Q

How are viruses classified?

A

Classified by nucleic acid composition

32
Q

What are the different types of latent infections?

A

Clinical and Molecular

33
Q

Describe clinical latent infections

A

1) Clinical latency
- A period in which no symptoms of infection are observed
- Viral/pathogen replication may or may not be present
- HIV - after acute phase, patients experience a long period of clinical latency, where no symptoms exist but viral replication occurs and CD4+ T cell counts diminish

34
Q

Describe molecular latent infections

A

2) Molecular latency
- A period in which no viral/pathogen replication occurs
- Features of latency vary by pathogen
- Herpesviruses - latent in neuronal or other cell types, express transcripts that prevent viral replication in order to hide from the host immune system

35
Q

What does PAMP stand for?

A

pathogen-associated molecular patterns

36
Q

Describe a PAMP response to infection

A 
Derive from pathogens, common molecular features that indicate infection are:
-LPS
-flagellin
-dsRNA
-bacterial cell wall components
CpG DNA
37
Q

What does DAMP stand for?

A

Danger-associated molecular patterns

38
Q

Describe a DAMP resonse to infection

A

Derive from physiological changes that indicate damage

  • ROS
  • changes in cytoplasmic CA+/K+ concentrations
  • ATP influx
  • Crystal deposition (MSU, etc.)
  • Membrane damage - mitochondrial, lysosomal, cell membrane

2nd year - Microbiology (21 decks)

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