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607 Virology > Viruses and Prions > Flashcards

Viruses and Prions Flashcards

1
Q

Reasons to Study Viruses?

A

-major source of disease
-limited anti-viral therapies
-One Health

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2
Q

What % of human viral infections have an animal origin?

A

70%

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3
Q

3 Components of the Definition of a Virus

A
  1. Obligate intracellular parasite (needs host cell)
  2. Submicroscopic (filterable) infectious agent
  3. Possess genetic material
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4
Q

Viral Small Size Exception

A

Megavirus from Chile was HUGE (1.2 million base genome)

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5
Q

Viral Genetic Material Exception

A

prions (do not contain nucleic acids)

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6
Q

Definition of Life

A

capacity to maintain an electrochemical gradient across a membrane (make ATP)

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7
Q

Are viruses living or non-living?

A

non-living

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8
Q

Do viruses have any biologically active membranes?

A

no

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9
Q

Modified Live Virus vs. Inactivated/Killed Virus Vaccine

A

modified live is still replication content versus killed are chemically inactivated

but NEITHER is living!

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10
Q

Envelope vs. Membrane

A

an envelope is non-living and does not function metabolically (despite being derived from the host cell)

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11
Q

3 Functions of RNA

A
  1. Can fold into complex structures
  2. Perform enzymatic activities (self-cleaving)
  3. Contain genetic information
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12
Q

Why is it thought that RNA-based organisms were the first “proto-life” forms?

A

you can find genes in modern RNA viruses that you can’t find anyplace else - evolutionary remnants

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13
Q

Koch’s Postulates

A
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14
Q

Polymicrobial Syndromes

A

“Death by a Thousand Cuts”
you’re not typically chasing after one big deadly virus, but it’s multiple things

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15
Q

The structure and physical composition of a virus provides essential information on what five things?

A
  1. Identification
  2. Pathogenesis
  3. Diagnosis
  4. Treatment
  5. Prevention
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16
Q

identification

A

how to classify it

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17
Q

pathogenesis

A

how it causes disease

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18
Q

diagnosis

A

how to detect it

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19
Q

treatment

A

how to control it

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20
Q

prevention

A

how to keep it out

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21
Q

2 Possible Virus Structures

A
  1. Non-enveloped
  2. Enveloped
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22
Q

Layers of a Non-Enveloped Virus

A
  1. Protein Capsid
  2. Nucleic Acid Genome
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23
Q

Layers of an Enveloped Virus

A
  1. Lipid envelope
  2. Protein capsid
  3. Nucleic Acid Genome
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24
Q

Where do enveloped viruses get their envelope from?

A

host cell membranes (nuclear, ER, Golgi, plasma)

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25
Q

Whose proteins are embedded in the lipid envelope - host or viral?

A

BOTH

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26
Q

capsid protein subunits

A

capsomeres, nucleocapsid proteins, nucleoproteins

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27
Q

Why is a capsid considered a “minimum structure?”

A

it is made to be the SMALLEST surface area that can encase a MAXIMAL volume

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28
Q

Why does a capsid need to be stable?

A

protects the nucleic acid genome

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29
Q

Why does a capsid need to be unstable?

A

it will need to be disassembled to allow the release of nucleic acid during replication

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30
Q

2 Protein Capsid Shapes

A
  1. Symmetrical
  2. Complex
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31
Q

2 Symmetrical Capsids

A
  1. Icosahedral
  2. Helical
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32
Q

Icosahedral Capsid

A

soccer ball, EPCOT

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33
Q

Helical Capsid

A

cylindrical with capsomeres arranged in a “spiral staircase” pattern around the genome
ex: rhabdovirus (rabies)

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34
Q

Complex Capsid

A

no symmetry, an absolute mumbo jumbo or nuclear proteins and nucleic acids

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35
Q

Two Types of Proteins in the Lipid Bilayer of the Virus Envelope

A
  1. Surface Glycoproteins
  2. Integral/Matrix Proteins
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36
Q

Origin of Surface Glycoproteins?

A

host OR virus

37
Q

Origin of Matrix Proteins?

A

viral protein, always

38
Q

Surface Glycoproteins

A

glycosylated, often appearing as spikes or protrusions on the envelope

39
Q

Matrix/Integral Proteins

A

non-glycosylated viral protein weaves in and out of the envelope to help stabilize it

40
Q

Budding

A

process by which the viral envelope is plucked from the host cell membrane and incorporates viral and host cell proteins

41
Q

Advantages of Enveloped Viruses

A
  1. Increased stability to virion
    2/ Facilitates entry into cell (lipid-lipid interaction helps promote fusion)
  2. Capsid disassembly
  3. Incorporation of host cell proteins into envelope gives a level of “camouflage”
42
Q

Possible Antiviral Drug Target?

A

hydrogen ion pore
If blocked, then the genome cannot be released into the cytoplasm

43
Q

Effect of pH on Capsid

A

a drop in pH causes capsid to fall apart

44
Q

Amantadine as an Anti-viral

A

Able to block the M2 H+ pore of the influenza virus

45
Q

Original goal of Amantadine?

A

developed in 1966 to treat Parkinson’s by increasing dopamine levels

46
Q

Do we still use amantadine as an antiviral today?

A

no - drug resistance developed!

47
Q

What does amantadine do to pigeons?

48
Q

Why do we not use antivirals often?

A

Drug resistance!!!!

49
Q

4 Classification Categories for Viral Nucleic Acid Genomes

A
  1. Nucleic Acid Composition
  2. Form of Nucleic Acid
  3. Polarity of ss Genomes
  4. Structure of Nucleic Acid
50
Q

Nucleic Acid Composition (2)

51
Q

Form of Nucleic Acid (2)

A
  1. Single Stranded (ss)
  2. Double Stranded (ds)
52
Q

Polarity for ss Genomes

A
  1. Positive sense
  2. Negative sense
53
Q

Structure of Nucleic Acid (3)

A
  1. Linear
  2. Segmented
  3. Circular
54
Q

Positive Sense Polarity

A

genome can be translated into protein directly

55
Q

Negative Sense Polarity

A

complementary copy most be made first

56
Q

Exception to the rules of virus genome polarity?

A

retroviruses - positive-sense single-stranded (ss)RNA viruses that replicate through a DNA intermediate via reverse transcription, and integrate into the genome of the host

57
Q

Prion Discovery

A

Stanley Pruisner 1982 - PROteinaceous INfectious particles, which were discovered while trying to purify a mysterious virus in sheep (Scrapie)

58
Q

Examples of Prions

A

Bovine Spongiform Encephalopathy (Cattle)
Scrapie (Sheep)
Transmissible Mink Encephalopathy (Mink)
Chronic Wasting Disease (Mule Deer, Elk)

59
Q

Are any species resistant to prions?

60
Q

5 Important Properties of Prions

A
  1. Resistant to heat, UV, and ionizing radiation (also formaldehyde)
  2. Protein only (NO nucleic acid)
  3. Transmissible (infectious)
  4. Filterable (small)
  5. Slow-acting, aggressive disease
61
Q

Do prions have a defined morphology?

A

no, no capsid

62
Q

What do prion infected brains look like?

A

Swiss cheese

63
Q

Can land ever become prion-free?

A

NO, animals can never be put back on that land

64
Q

prion incubation period

A

LONG (take a two year vacation)

65
Q

PrPc

A

host-encoded prion, exists naturally, primarily alpha helix conformation

66
Q

PrPSc

A

scrapie form, or modified “infectious” form, converted from PrPc; now has primarily beta sheet conformation

67
Q

Three Ways Prion Conformation Change Occurs

A
  1. Spontaneously
  2. Gene mutation (includes inherited form)
  3. Infectious (get PrPSc from infected animal)
68
Q

Which conformation change is arguably the most dangerous?

A

spontaneous!

there’s no prevention, so you can’t quarantine

69
Q

prion infection as a self-propagation event

A

PrPSc binds to normal (PrPc) and converts it to the Scrapie form, acting as a chaperone

70
Q

Infectious Disease Process of Prions

A

ingestion of PrPSc
move from intestine to brain via bloodstream or possibly neurons
neurons in brain uptake infectious form, where conversion of PrPc in host begins
no possible removal; accumulates in amyloid-like plaques
sponge-like holes left in brain

71
Q

Diagnosis of Prion Disease (4)

A
  1. Necropsy of brain material
  2. Propagation Assays
  3. Antibody-based assays
  4. Sequencing
72
Q

Propagation Assays

73
Q

Limitation of Propagation Assays

A

takes time!

74
Q

Antibody-based assays

A

use unique epitopes on the PrPSc to bind antibody

75
Q

Is there any evidence of prion resistance?

A

YES

Fore tribe tradition in Papau New Guinea has a mutation in the PrPc gene making it resistant to conversion to the infectious form of Kuru

76
Q

Mutation in Fore Tribe is specifically?

A

conversion of glycine 127 to valine

77
Q

Which is more susceptible - enveloped or non-enveloped viruses?

A

enveloped

lipids are much more susceptible to degradation than the capsule; when an envelope disintegrates, the capsid also goes away

78
Q

Why is species not a commonly used in virus classification?

A

species technically means it can produce viable offspring, which viruses cannot, they abstain from sexual activity

79
Q

Current Virus Classification System is maintained by ____________ (ICVT)

A

International Committee on Viral Taxnomy

80
Q

Current Virus Classification System (4)

A
  1. Presence or absence of envelope
  2. Capsid symmetry
  3. Viral genome characteristics
  4. Nucleotide sequence
81
Q

Old Methods of Virus Classification (2)

A

-Host range or disease (mouse hepatitis virus)
-Serological relationship (serotypes)

82
Q

Virus Order Suffix

83
Q

Virus Family Suffix

84
Q

Virus Subfamily Suffix

85
Q

Virus Genus Suffix

86
Q

What is used in place of species for viruses (options)?

A

isolate, strain, group, genotype, serotype, common names

87
Q

Examples of Virus Classification (just for looking)

A

these are just for you to look at, don’t panic

88
Q

and he said to the man, running the stand, “hey, ___________”

607 Virology (13 decks)

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