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DMD 5245 > Virus replication, structure, and classification (complete) > Flashcards

Virus replication, structure, and classification (complete) Flashcards

1
Q

how do viruses replicate

A

by assembly of subunits in infected cells

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2
Q

What are the steps for viral replication

A
  1. attachement
  2. penetration
  3. uncoating
  4. early transcription
  5. early translation
  6. replication
  7. late transcription
  8. late translation
  9. assembly
  10. release
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3
Q

What are the two ways that viruses can kill

A

causing an overactive immune system (angry macrophages)

inhibiting the immune system

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4
Q

what is the primary example of a virus that kills by causing an over active immune system

A

influenza

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5
Q

what is the primary example of a virus that kills bu inactivating the immune system

A

Ebloa (also HIV)

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6
Q

What is the main difference between positive and negative RNA virus replication

A

a positive strand is just like mRNA so it is immediately translated, negative strand mRNA has have a complementary strand made, then have that one translated

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7
Q

although positive and negative RNA virus replication is different, what is one important similarity

A

they both create double stranded RNA

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8
Q

why is double stranded RNA so important

A

it is the signal that induces the synthesis of interferon

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9
Q

can viruses resist interferon action

A

yes

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10
Q

what is a retrovirus

A

an RNA virus that goes from RNA to double stranded DNA.

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11
Q

what is needed by a retrovirus, and can be the target of antiviral drugs

A

RT

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12
Q

What is the main target of antibodies against viruses

A

antibodies against particles on the viral envelope, this prevents them from binding to the cell

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13
Q

What are the different outcomes of a viral infection for the cell

A
  1. Abortive infection
  2. Latent infection (can become a productive infection)
  3. productive infection (can lead to cell death or a persistent infection)
  4. apoptosis
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14
Q

What are the four immune mechanisms that fight viruses and what do they cause

A
  1. interferon - blocks infection, kills infected cells
  2. NK cells - kill infected cells
  3. B cells/antibody - neutralizes viruses, enhance phagocytosis
  4. Cytotoxic T-cells - kills infected cells
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15
Q

What are the TLRs that are important to antiviral activity

A

TLR 3, 7, 8, and 9

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16
Q

What does TLR3 recognize and result in

A

TLR 3 recognizes DsRNA and produces IFN-beta

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17
Q

what do TLR 7, and 8 recognize and result in

A

they recognize viral ssRNAand produce IFN-1 alpha

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18
Q

What does TLR 9 recognize and result in

A

it recognizes unmethylated CpG, and results in IFN-alpha

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19
Q

what type of cell produces the most IFN-alpha

A

plasmacytoid dendritic cells

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20
Q

what is the sequence of events from TLR recognition to IFN production

A
  1. TLR recognition
  2. signal pathway
  3. transcription factors
  4. Interferon production
  5. Release of interferon
  6. protection of non-infected cells
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21
Q

What is type 1 interferon

A

IFN alpha and beta

produced by immune cells and infected cells

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22
Q

what is type 2 interferon

A

antiviral and defense against intracellular bacteria and parasites
produced by immune cells only

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23
Q

What are the three ways in which interferons work

A
  1. they inhibit all translation (type 2 IFN only does this)
  2. they degrade mRNA and rRNA
  3. they inhibit transcription, and viral assembly
    (type 1 IFN does all three)
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24
Q

What does STAT do?

A

it causes IFN to be produced

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25
Q

how can viruses evade antiviral defenses

A
  • Influenza NS1 binds to dsRNA
  • Ebola prevents dsRNA from inducing IFN release
  • Ebola inhibits RNA silencing
  • adenovirus blocks STAT1 from functioning
  • Vaccinia prevents IFN from attaching
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26
Q

What are the two ways that a virus can initiate apoptosis

A

extrinsic (death by instruction)

intrinsic (death by stress)

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27
Q

how is apoptosis carried out

A

activation of caspases, which basically chew everything in the cell up, then they are and ingested by phagocytes

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28
Q

is apoptosis good or bad for the virus inside the cell

A

it can be both. Some viruses initiate apoptosis, others prevent it so the cell will stay live and produce more virus

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29
Q

What is a latent viral infection

A

the viral genome is present, but there are no infectious viral particles

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30
Q

What is lysogeny

A

when a viral genome integrates into the host genome

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31
Q

what is an episomal viral genome

A

when a viral genome isn’t entered into the host chromosome (like a bacterial plasmid)

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32
Q

which viruses cause chronic inflammation

A

Hep B and C

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33
Q

which viruses can cause cancer

A

Hep B and C

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34
Q

what is a viral oncogene

A

cancer causing genes in sarcoma and leukemia viruses

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35
Q

What is tropism

A

the increased ability of a virus to replicate in certain cells or tissues

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36
Q

what controls tropism

A
  1. viral antireceptor
  2. viral receptor
  3. route of infection
  4. transcription factors
  5. immune system response
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37
Q

What happens to a host with a viral infection

A

IL-1 - causes fever, somnolence, anorexia, lowers libido, lowers pain threshold
IFN - causes nausea, vomiting, fever, chills, fatigue, malaise, asthenia, myalgia, leukopenia
TNF-alpha - causes inflammation, cachexia, fever, cell lysis

38
Q

What are acute viral infections

A

rapid onset, rapid resolution (virus is cleared)(influenza)

39
Q

what are chronic viral infection

A

slow onset, slow resolution, cells die, infection spreads (HBV, HIV)

40
Q

what are persistent infections

A

virus stay with the host, infected cells live (retroviruses)

41
Q

what are latent infections

A

virus stays with the host, reactivation episodes occur (HSV) start and end as acute infections

42
Q

What is a subclinical viral infection

A

an infection with no signs or symptoms, but infectious virus is produced and transmittable

43
Q

What is a virus

A

a very small non-cellular parasite of cells.

44
Q

What are the parts of a virus

A

a DNA or RNA genome
a Capsid (protein coat)
sometimes an envelope

45
Q

are there parts of our genome that are retroviral sequences

A

yes, our genome is about 8% retroviral

46
Q

What is the newest theory on origin of viruses

A

that viruses preceded cellular organisms

47
Q

What is a virion

A

an infectious virus particle

48
Q

can viruses sustain themselves and replicate

A

no, they are obligate intracellular parasites (they can’t produce energy or synthesize ribosomes)

49
Q

What is a capsid

A

a protective protein shell for the viral genome, composed of capsomers

50
Q

what are capsomers

A

the structural components (bricks) of the capsid, they are made of protomers

51
Q

what are protomers

A

the building blocks that make up capsomers

52
Q

What are the functions of viral proteins

A
  1. structural
  2. protect genome
  3. attachment to host cell
  4. fusion with cell membrane
  5. Enzymes
  6. primers
  7. immune interference
53
Q

how are capsids build

A

they self-assemble, due to reactions with large free energy that proceed to near completion

54
Q

are all of the components made by viruses for replication used to make new viruses

A

no, probably not even close, but enough are that the virus still successfully replicates

55
Q

what is a virion composed of

A

it is the infectious virus particle, that is composed of RNA or DNA, proteins, and sometimes an envelope

56
Q

where is the envelope a virus sometimes has obtained from

A

from a modified cell membrane

57
Q

What are the two main structures of capsids

A

helix and icosahedron

58
Q

what are the functions of the capsid

A
  1. protect the genome from nucleases and other hostile things
  2. necessary for the infectivity of virions
  3. in naked viruses it serves as the attachment protein
  4. it is antigenic and invokes an immune response
59
Q

how many capsid layers do viruses have? any excpetions

A

1

yes, reoviridae has 3 capsid layers

60
Q

what is the helical structure of capsids like

A

it looks like a stack of washers. it is a long tightly coiled protein

61
Q

What are the shapes that a capsid with helical symmetry can make

A

sphere
bullet
Rod
thread

62
Q

What is the capsid of rhabdovirus (rabies) like

A

helical capsid
tight envelope
bullet shaped

63
Q

What is the capsid of the influenza virus like

A

helical capsid
loose envelope
sphere shaped

64
Q

What is an icosahedra

A

a structure with
20 equilateral triangles
30 edges
12 verticies

65
Q

how many axis of symmetry do icosahedra have

A

3
5 fold
2 fold
3 fold

66
Q

what is the minimum number of subunits that can make up a face in an octahedron

A

3

67
Q

what is the minimum number of subunits a whole icosahedra can have

A

60 (3 per face x 20 faces)

68
Q

how do you get larger icosahedra

A

by adding more subunits per face, not by making larger subunits

69
Q

What can you have external to the capsid

A

an envelope (sometimes you do, sometimes you don’t, that depends on the virus)

70
Q

Which virus has a brick shaped capsid

A

poxvirus

71
Q

What are the 4 different types of viral capsids we study

A
  1. naked icosahedral
  2. envelopped icosahedral
  3. naked helical
  4. envelopped helical
72
Q

what are the 4 different types of viral genomes

A
  1. single stranded RNA
  2. double stranded RNA
  3. single stranded DNA
  4. double stranded DNA
73
Q

what shapes do the viral genomes take

A

circular or linear

74
Q

what other modifications can viral genomes have

A

they can be incomplete double stranded

they can be segmented (more than one piece)

75
Q

What is a positive strand RNA

A

one that has the same polarity as mRNA (5’-3’)

76
Q

what is a negative strand RNA

A

one that has the opposite polarity as mRNA (3’-5’)

77
Q

What are the three different types of viral DNA genomes

A
  1. double stranded with open ends
  2. double stranded with closed ends
  3. single stranded
78
Q

what are the 4 different types of viral RNA genomes

A
  1. single stranded +
  2. single stranded -
  3. double stranded
  4. single stranded, segmented
79
Q

Which strand, positive or negative, ssRNA needs to bring its own RNA dependent RNA polymerase

A

the negative strand RNA, this way it can make its own complementary copy

80
Q

How are viruses classified

A
  1. DNA or RNA
  2. Icosahedral or Helical
  3. Naked or Envelop
  4. Double Stranded, Single Stranded
    • or -
81
Q

What are the characteristics of the influenza virus (orthomyxo)

A
  1. RNA
  2. Helical
  3. Enveloped
  4. Single Stranded (8 SEGMENTS)
  5. Negative
82
Q

What are the characteristics of the paramyxo virus

A
  1. RNA
  2. Helical
  3. Enveloped
  4. Single Stranded (non-segmented)
  5. Negative
83
Q

What are the characteristics of the Filo (ebola) virus

A
  1. RNA
  2. Helical
  3. Enveloped
  4. Single Stranded (non-segmented)
  5. Negative
84
Q

What are the characteristics of the Corona virus (sore throats)

A
  1. RNA
  2. Helical
  3. Enveloped
  4. Single Strand
  5. Positive
85
Q

What are the characteristics of the Picorna virus (common cold)

A
  1. RNA
  2. Icosahedral
  3. Naked
  4. Single Stranded
  5. Positive
86
Q

What should we remember about helical DNA viruses

A

there are no helical DNA viruses that affect humans

87
Q

What are the characteristics of the herpes virus

A
  1. DNA
  2. Icosahedral
  3. Enveloped
  4. Double Stranded (linear)
88
Q

What are the characteristics of the hepadna virus (HEP B)

A
  1. DNA
  2. Icosahedral
  3. Enveloped
  4. Double Stranded (circular - gapped)
89
Q

What are the characteristic of the Adeno (upper respiratory) virus

A
  1. DNA
  2. Icosahedral
  3. Naked
  4. Double stranded (linear)
90
Q

What are the characteristics of the Papilloma virus (HPV)

A
  1. DNA
  2. Icosahedral
  3. Naked
  4. Double Stranded (circular)

DMD 5245 (15 decks)

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