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OD2 S1 > M: Virology 1 - Week 11 > Flashcards

M: Virology 1 - Week 11 Flashcards

1
Q

What is a virus? (2)

A

An infectious, obligate intercellular molecular parasite containing a DNA or RNA genome that is packaged into a virion particle from host to host

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2
Q

What do viruses require for replication?

A

Totally dependent on a living host cell for propagation and replication

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3
Q

What type of genome do viruses have? (2)

A

DNA or RNA genome

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4
Q

Is the viral genome single or double stranded?

A

Can be either

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5
Q

How big are viruses compared to bacteria? What about compared to eukaryotic cells?

A

Small compared to bacteria
Very small compared to eukaryotic cells

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6
Q

How does virus receptor-binding compare between viruses?

A

Specific: each virus has a receptor-binding/virus-attachment protein for initial contact with host cell receptors and entry into target cell

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7
Q

How are new virus particles assembled?

A

Are assembled from new viral components synthesised in infected cells

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8
Q

What is the information contained in viral genomes used for?

A

Viral genomes contain all the information to initiate and complete an infectious cycle

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9
Q

What are the 2 phases of a virus?

A

Virion
Infected cell

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10
Q

Define Virion

A

The complete, infective form of a virus outside a host cell, with a core of RNA or DNA that is either single or double stranded, and a capsid

(Also: an archer from fire emblem awakening. A very posh and flamboyant man)

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11
Q

What is a capsid?

A

A protective protein coat for the genome

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12
Q

Are viruses cells? Explain

A

No!
Viruses contain NO ribosome machinery for protein synthesis

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13
Q

What is the size range for viruses? What is noteworthy about this?

A

Range from 20nm to 250-300nm

These sizes are too small to see on a light microscope. Need an electron microscope to view

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14
Q

What is necessary for sucessful electron microscopy of viruses? (2)

A

Require pure particles with proven infectivity
Negative staining also necessary

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15
Q

What can you use for negative staining of viruses in electron microscopy?

A

Potassium phosphotungstate

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16
Q

What does X-ray crystallography of viruses require?

A

Computer for image reconstruction of virus

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17
Q

What does the virion sometimes posses?

A

An envelope made of cell membrane modified to contain virus proteins

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18
Q

What are capsomers?

A

Clusters of capsid protein subunits

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19
Q

What is an envelope?

A

A lipoprotein membrane surrounding either nucleocapsid or capsid

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20
Q

What is a nucleocapsid?

A

The proteins most closely assembled onto the viral nucleic acid (sometimes this IS the capsid protein)

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21
Q

Where are the phospholipids of the envelope derived from?

A

From the host cell membrane

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22
Q

What codes the glycoproteins of the virus envelope?

A

Virus-encoded

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23
Q

What is a virus matrix?

A

A layer of protein that connects the capsid to envelope glycoproteins

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24
Q

Name the 2 different forms of capsid symmetry

A

Icosahedral capsid
Helical capsid

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25
Q

What are the 3 different axes for the icosahedral symmetry

A

Twofold axis
Threefold axis
Fivefold axis

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26
Q

Provide 3 examples of viruses with icosahedral symmetry

A

Adenovirus
Herpesvirus
Papillomavirus

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27
Q

What 2 conditions do adenoviruses cause?

A

Respiratory illness
Conjunctiva

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28
Q

How many species of herpesvirus are there? Name 4

A

8
HSV
Cytomegalovirus
Varicella zoster
EBV

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29
Q

What does papillomavirus cause?

A

causes warts. These warts can become malignant (on genitals)

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30
Q

Describe the architecture of helical capsid symmetry. What does it look like?

A

A planar net of identical protein subunits wraps around the nucleic acid to form a protective layer

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31
Q

Provide 2 examples of viruses with nucelocapsids of helical symmetry

A

Mumps virus
Influenza virus

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32
Q

What symmetry do poxyviruses have?

A

They are an exception to the rule and have neither icosahedral nor helical symmetry. Their symmetry is COMPLEX

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33
Q

Which virus is the largest?

A

Poxyviruses are the largest

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34
Q

How many different proteins are present in the poxyvirus virion?

A

Over 100

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35
Q

What symptom does rotavirus infection typically cause?

A

Diarrhea (in children)

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36
Q

Is Rotavirus considered hardy or sensitive? Why?

A

Hardy. It survives passage through the gut and even sewage treatment.

  • this is because it has 2 protein layers (outer and inner capsid) that protect the inner nucleic acid
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37
Q

What is meant by the term “Naked Virus”?

A

A virus that has no envelope

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38
Q

Does rotavirus have an envelope?

A

No. It is a naked virus

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39
Q

Do viruses with envelopes or naked viruses kill the cell upon leaving?

A

Naked viruses kill the cell. The envelope allows the virus to leave without killing the cell.

40
Q

Is influenza an enveloped virus or naked virus?

A

enveloped virus

41
Q

What is the envelope for the influenza virus derived from?

A

derived from the plasma membrane of cells

42
Q

Which kind of virus is more resistant to environmental conditions: enveloped virus or naked virus? Why?

A

Naked virus.

Lipid envelops are quite fragile and sensitive to denaturation (heat/cold/pH) they are more likely to be denatured and then the virus loses infectivity.
This is not the case with non-enveloped/naked viruses.

43
Q

What forms can the genome of viral nucleic acid be found in? (4)

A

may be:
S.S DNA
D.S DNA
S.S RNA
D.S RNA

s.s = single-stranded. d.s = double-stranded

44
Q

Which kinds of viral nucleic acid genome can form complex structures? (2)

A

ss DNA and ss RNA

45
Q

What are virus families classified by? (3) (technically 8 I guess actually)

A

Kind of nucleic acid genome, and arrangement (order) or genes
Morphology of the virion (capsid symmetry, +/- envelope, size, appearance)
Strategy of viral replication

46
Q

What does the family name for viruses end in? How are virus family names written?

A

-viridae

written in italics

47
Q

Define genus

A

a group of species sharing certain common characteristics

48
Q

What are genera classified by? (4)

(note: genera = plural of genus)

A

size of genome and sequence differences
number and size of proteins
serological reactivity
host range and disease produced (sometimes)

49
Q

What do the names for genera end in?

A

-virus (e.g. lentivirus)

50
Q

Are icosohedral viruses enveloped or naked?

A

Can be either

51
Q

Are helical viruses enveloped or naked?

A

All of them are enveloped

52
Q

What does it mean for a viral RNA genome to be “positive sense?”

A

Positive-sense (5’ to 3’) viral RNA signifies that a particular viral RNA sequence may be directly translated into the desired viral proteins. Therefore, in positive-sense RNA viruses, the viral RNA genome can be considered viral mRNA, and can be immediately translated by the host cell.

53
Q

Which viruses contain a virion polymerase: viruses with a positive sense genome or viruses with a negative sense genome? Why

A

Viruses with a negative-sense genome contain a virion polymerase

positive-sense genomes can act as mRNA to directly synthesise proteins without the help of a complementary RNA intermediate - i.e they don’t need a virion polymerase

54
Q

How are retroviruses considered the exception to the rule for virion polymerase?

A

They contain virion polymerase despite being a positive-sense genome

55
Q

What is virion polymerase?

A

An enzyme capable of replicating the genome

(a.k.a. RNA-dependent RNA polymerase: catalyses the replication of RNA from an RNA template)

56
Q

Out of the viruses we should know about, which is the only virus that is double stranded?

A

Reoviridae

57
Q

Where do enteric viruses primarily replicate?

A

Intestinal tract

58
Q

How are enteric viruses acquired?

A

ingestion (e.g. rotavirus, calicivirus, astrovirus, some adenoviruses)

59
Q

Where do respiratory viruses primarily replicate?

A

respiratory tract

60
Q

How are respiratory viruses acquired?

A

inhalation of droplets

61
Q

What do Arboviruses infect? How are they transmitted?

A

infect insects and are transmitted by bite to mammals

62
Q

Name 4 arboviruses

A

orbivirus
most bunyaviruses
flaviviruses
togavirus

63
Q

How are sexually transmitted viruses transmitted? (lol)

A

sexually

64
Q

What is the principle target for hepatitis viruses?

A

Liver

65
Q

How are the 5 hepatitis viruses spread? (2)

A

Hep A + E: spread by enteric route
Hep B + C + D: spread by blood or sexually

66
Q

True or False: Hepatitis viruses all belong to the same taxonomic family

A

False. Each has a different taxonomic family

67
Q

Why can a laboratory diagnosis be useful for a virus? (3)

A

Useful for:
Deciding treatment options (some viruses are slow/persistent, so tx useful)
Public Health measures
Surveillance

68
Q

Name 3 general treatment options that could be implemented for a virus

A

chemotherapy
passive immunization
abortion (extreme)

69
Q

Name 2 public health measures that could be taken against a virus

A

Blood bank screening (for HIV, HBV, HCV)
Contact monitoring/treatment

70
Q

Name 5 methods of viral detection

A

Direct visualisation by electron microscopy
Viral cultivation
Viral protein (antigen) detection
Host serological response
Viral gene detection

71
Q

What method of viral detection was considered the gold standard? (15 years ago)

A

Viral cultivation

72
Q

What are the disadvantages of viral cultivation? (3)

A

Some viruses have NO culture system (e.g. HCV) so can’t be cultured
Slow
Result often too late to impact on treatment

73
Q

What determines what clinical samples you should take for virus identification?

A

samples taken depends on the disease syndrome

(e.g. if eye, take tear/conjunctival swab)

74
Q

How are clinical samples for viral identification transported to the laboratory?

A

samples are refrigerated or frozen in buffered “transport medium” for transfer to the lab

75
Q

How well do enveloped viruses survive outside host cells?

A

poorly

76
Q

What are 3 techniques we can use to help preserve viral infectivity for cultivation?

A

Use low temperature
Freeze drying (some viruses)
Buffered transport medium

77
Q

What temperature should we store viruses in for a day or so? (to preserve viral infectivity)

A

4 degrees celsius

78
Q

What temperature should we store viruses in for long term storage? (to preserve viral infectivity)

A

-70 degrees celsius

79
Q

What temperature should we store viruses in for permanent storage? (to preserve viral infectivity)

A

-196 degrees celsius

80
Q

When storing viruses to preserve viral infectivity, what should be avoided?

A

avoid repeated freezing and thawing

81
Q

How does freeze-drying a virus work?

A

dehydration of a frozen suspension under vacuum

82
Q

How often is direct visualisation by EM used? Name an instance

A

Mostly not used. Can be used for certain cases such as high concentration of rotavirus

83
Q

Name 3 virus cell cultures we can have

A

Animal culture (e.g. suckling mice)
Embryonated egg culture
Mammalian cells

84
Q

What types of mammalian cells are used in cell culture? (3)

A

Primary cells: prepared from animal tissue
Diploid cell lines: have limited lifespan in culture
“Transformed” or “continuous” cell lines: can be passaged indefinitely in vivo

85
Q

What are inclusion bodies?

A

Inclusion bodies represent accumulated viral proteins at the site of virus assembly

86
Q

What type of inclusions do adenovirus-infected cells present with?

A

nuclear inclusions

87
Q

What type of inclusions do reovirus-infected cells present with?

A

cytoplasmic inclusions

88
Q

What happens to measles virus during replication?

A

fusion of neighbouring cells and the formation of multi-nucleated cells or syncytia

89
Q

Name 2 serological assays for viruses. Do they have high sensitivity or high specificity? (2)

A

Antigen capture assay (HIV p24 assay) = High sensitivity
Anti-viral antibody assay (HIV “western blot”) = High specificity

90
Q

Which serological assay is considered the principle diagnostic for HIV infection?

A

Antigen capture assay (HIV p24 assay)

91
Q

Describe the following features of infectivity/serology assays:
- speed
- sensitivity of viral antigen detection

A

Generally slow
High sensitivity (therefore can result in false positives)

92
Q

Describe a methodology for more rapid detection of viral nucleic acids (6)

A

Southern blot for viral DNA
Northern blot for viral DNA
PCR for DNA
Reverse-transcriptase PCR for RNA
Viral nucleic acid sequencing
DNA microarray technology

93
Q

How deep is viral nucleic acid sequencing?

A

Deep sequencing of everything that is there

94
Q

What is the sensitivity and specificity of a PCR assay?

A

High for both

95
Q

In regards to a PCR assay:
- how fast?
- how much sample?
- how cheap?
- how easily adaptable?
- is it automated?

A

Very fast
Low amount sample
Cheap
Easily adapted
yes its automated

OD2 S1 (47 decks)

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