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Virology > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

How do viruses reproduce?

A

In host’s cell

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2
Q

How are viruses classified?

A

International Committee on Taxonomy-genome and nucleic acid material
Baltimore-type of their genome (dsDNA, ssDNA, …)

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3
Q

What are the main components of a virus?

A

Genomic material (DNA, RNA)
Capsid (protein shell)
Nucleocapsid
Envelope (host cell membrane and viral proteins)

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4
Q

What are the forms of RNA a virus can have? BTW RNA has a small genome compared to DNA viruses

A

Singe (positive or negative)

Double (one piece or segmented)

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5
Q

What are the forms of DNA a virus can have?

A

Single or double

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6
Q

What are the two building block units of a viral capsid?

A

Helical (protein units form a tube)

Icosahedron (like a soccer ball)

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7
Q

What are the benefits and pitfalls of a viral capsid?

A 
Transfers easily
Still infective even if dried out
Survives in adverse conditions
Resistant to detergents 
Ab might be sufficient for immunoprotection
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8
Q

What must all negative RNA viruses have?

A

An envelope

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9
Q

What are the benefits and pitfalls of viral envelope?

A

Must stay wet
Can’t survive GI tract
Spreads in large drops, secretions, organ transplants, blood transfusions
Can spread without killing host cell
May need Ab and cell-mediated immune response for protection and control
Elicits hypersensitivity and inflammation to cause pathogenesis

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10
Q

What are the major steps in viral replication that are conserved across species?

A

Recognize target cell and attach
Penetrate and uncoat
Macromolecular synthesis (this varies throughout the replication phase)
Assembly
Budding of enveloped viruses and/or release

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11
Q

When a virus pentrates a cell it is not infective. Why?

A

It uncoats once it enters (called eclipse).
During this latent period replication occurs.
Then the maturation period of assembly.
Finally release.

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12
Q

How do viruses recognize their target cells?

A

Via receptors.

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13
Q

What are the two ways a non-enveloped virus can enter a cell?

A

Receptor mediated endocytosis

Viropexis which is direct penetration (I think genetic material is injected directly into the cell)

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14
Q

How does an enveloped virus enter a cell?

A

Fusion of membranes (pH dependent)
Neutral pH endocytosis and then fusion occurs in an endosome (at acidic pH)
Then the vesicle, envelope and capsid break down

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15
Q

How do dsDNA viruses replicate?

A
  1. Use machinery in nucleus to make RNA and then ribosomes

2. Replicate viral genome (DNA polymerase from cell)

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16
Q

How do ssDNA replicate?

A
  1. Use cell DNA poly to copy (+) DNA which makes dsDNA
  2. Then copy use DNA poly again to make an additional (+) DNA for the next virus
  3. Use dsDNA to make mRNA and then use ribosomes
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17
Q

How do dsRNA replicate?

A
  1. RNA-dependent RNA polymerase to make second dsRNA
  2. Viral RNA-dependent RNA polymerase to copy (-) RNA into (+) mRNA
  3. (+) mRNA into proteins
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18
Q

How do (-) RNA replicate?

A
  1. Viral RNA dependent RNA polymerase (transcriptase) to copy (-) into (+)
  2. Viral RNA dependent RNA polymerase (replicase) copy copy (+) into minus for increased genome
  3. (+) RNA used as mRNA for protein synthesis
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19
Q

ssRNA (+) replication

A
  1. Viral RNA dependent RNA polymerase (replicase) to copy (+) into (-) RNA
  2. Viral RNA dependent RnA polymerase (replicase) to then use (-) to remake (+)
  3. (+) RNA used as mRNA
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20
Q

RNA (+) retrovirus replication

A
  1. Viral reverse transcriptase copies (+) RNA into (-) ssDNA
  2. Viral reverse transcriptase copies (-) ssDNA into dsDNA
  3. DNA will move to nucleus and integrate into host DNA
  4. Host DNA dependent RNA polymerase copies (-) strand of dsDNA into (+) RNA (for genome replication and also for protein synthesis)
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21
Q

What are the differences between early and late stage protein synthesis during viral replication?

A
  • Early: Proteins for replication of viral genome are made

* Late: Proteins for viral structure and enzymes for maturation are made

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22
Q

What must be present so that a virus can make synthesized proteins functional?

A
  • A protease

* Viral proteins are made in a long strand and it needs to be cleaved

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23
Q

What is a monocistronic virus?

A

Virus contains genetic material to translate only a single protein

24
Q

What is a polycistronic virus?

A

Virus contains transcripts of several genes and are translated into one or more large polypeptides which are then cleaved

25
Q

What dictates where a virus is finally assembled?

A
  • Where genome replication takes place

* Whether final structure is a naked capsid or envelope

26
Q

Where do DNA viruses assemble?

A
  • In nucleus

* Pox virus is an exception where this does not occur

27
Q

Where do RNA viruses assemble?

A
  • In cytoplasm

* Pox is DNA but assembles in cytoplasm

28
Q

How do enveloped viruses get their envelope?

A
  • Nucleocapsid picks up membrane in a process called budding
  • Matrix proteins promote this adhesion and budding
29
Q
  • How do non-enveloped and complex viruses leave a cell?

* Why do complex viruses have this reaction?

A
  • Cell lyses

* Complex: Because of the immune reaction

30
Q
  • How do enveloped viruses leave a cell?

* What is the special condition for one of the methods?

A
  • Budding

* Exocytosis: if viruses acquires envelope in the cytoplasm (result of budding from nuclear or Golgi membrane)

31
Q

Herpes simplex is what kind of virus?

A
  • Enveloped, DNA virus

* Review specifics of its replication (lecture 1, slide 36)

32
Q

Picornavirus is what kind of virus?

A
  • (+) RNA

* Review specifics of it’s replication (lecture 1, slide 37)

33
Q

Rhabdovirus is what kind of virus?

A
  • Enveloped (-) RNA

* Review specifics of it’s replication (lecture 1, slide 38)

34
Q

What are the three types of viral infections?

A
  • Failed-abortive infection
  • Acute
  • Persistent/chronic
35
Q

What is characteristic of an acute viral infection?

A
  • Lytic in nature
  • Rapid onset
  • Relatively short duration
36
Q

What is characteristic of a chronic viral infection?

A
  • Can last many years
  • Almost always detectable
  • Symptoms may be mild or absent for long periods of time
37
Q

What is a nonpermissive cell?

A

A cell that does not allow replication of a particular type or stain of virus

38
Q

What is a permissive cell?

A

Provides biosynthetic machinery to support complete replicative cycle of virus

39
Q

There are four main types of chronic viral infections. What are they?

A
  • Chronic infetion (non-lytic, productive)
  • Latent (virus stops reproducing, not detectable at this time)
  • Recurrent infection
  • Transforming (permanently alters hosts genetic material resulting in cancer)
40
Q

A virus capable of initiating a tumor is called what?

A

Oncovirus

41
Q

What virus can cause cervical cancer?

A

Papillomavirus

42
Q

What virus can cause Burkitt’s lymphoma?

A

Epstein-Barr virus

43
Q

What are mechanisms of transmission of a virus when it’s already in the host?

A
  • Viremia (spread of microbe via blood)
  • Neurons
  • Cell to cell
  • Fusion (syncytia)
  • In transformed or infected cell
44
Q

What are the mechanisms that allow a virus to hurt a cell?

A
  • Diversion of cellular energy
  • Shutdown macromolecular synthesis
  • Competition of viral mRNA for ribosomes
  • Competition for replication factors
  • Inhibiting interferon and shutting down host’s defense
  • Activating host immune response
45
Q

When a virus infects a cell it can cause changes to the cell. What are these called?

A
  • Virus-induced cytopathological effects (CPEs)

* Change in morphology, cell lysis, vacuolation, syncytia, inclusion bodies

46
Q

What are three ways you can grow a virus?

A
  • Tissue culture (routinely used)
  • Embryonated eggs (vaccines)
  • Animals (rarely used)
47
Q

Prions cause what broad class of disease?

A

Transmissible Spongiform Encephalopathies (TSEs)

48
Q

What will you not find with a TSE?

A
  • Absence of cerebrospinal fluid pleocytosis

* No changes in clinical chemistry or hematological values

49
Q

How do prions replicate?

A
  • They catalyze fellow proteins to fold into insoluble β-pleasted sheets
  • Induce different post-translation modifications of normal host protein
50
Q

Prions are only abnormal when they are misfolded. Where are they normal?

A

When they are in α-configuration (sensitive to protease degradation)

51
Q

Why is there no immunological response to prion disease?

A

Because they are naturally occurring proteins

52
Q

Creutzfeldt-Jakob disease characteristics

A
  • Dementia → death (within 1 year)
  • Spontaneous occurrence
  • Not transmittable
  • People > 50
  • Might have muscle involvement in advanced disease
53
Q

Variant Creutzfeldt-Jakob disease details

A
  • Younger patients (28-29)
  • Duration 14 months resulting in death
  • Possibly linked to food exposure through cattle
  • Early: might resemble depression, schiozphrenia-like psychosis
  • Late: Unsteadiness, ataxia, involuntary movements
  • After ingestion, these prions disseminate throughout the body including CNS
54
Q

What type of lesions do prions form?

A

Non-inflammatory amyloid plaques

55
Q

How do you diagnose CJD

A

Specific EEG findings (not present for vCJD)

56
Q

What is a satellite virus?

A

Virus that is dependent on other viruses for replication (adeno-associated virus,

Virology (4 decks)

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