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MICRO > L9: Introduction to Virology > Flashcards

L9: Introduction to Virology Flashcards

1
Q

Are viruses living?

A

No

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2
Q

Define virus?

A

Obligate intracellular parasite lacking capacity to make energy or substrates

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3
Q

Can viruses be replicated outside of a cell?

A

No

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4
Q

Replication occurs how in viruses?

A

Assembly of parts, NOT binary fission

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5
Q

What is a defective virus?

A

Genetic mutation that prevents replication without a helper virus?

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6
Q

What is a pseudovirus?

A

Has host DNA in capsid instead of viral nucleic acid?

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7
Q

Pseudoviruses play a role in what bacterial genetic transfer?

A

General transduction (Bacteriophage)

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8
Q

What is a viroid?

A

Single circular RNA without a capsid

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9
Q

What do viroids usually attack?

A

Plants

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10
Q

90% of viruses are which of the three types?

A

Defective

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11
Q

What is the origin of viruses?

A

unknown

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12
Q

How is a virus structured?

A

Nucleic acid (RNA or DNA) surrounded by a protein coat

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13
Q

Protein coat of viruses is called what?

A

capsid

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14
Q

Viruses can only be seen under what?

A

EM

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15
Q

The nucleic acid of viruses can be what?

A
  1. DNA (3.2kb to 375kb)

2. RNA (7 to 30kb)

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16
Q

Are viruses haploid or diploid

A

Haploid except for retroviruses that are diploid

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17
Q

The capsid is made up of what?

A

Capsomeres making pentamers and hexons

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18
Q

What gives virus its shape?

A

Capsid (number of hexons and pentamers)

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19
Q

Capsomeres need what to assemble into larger units?

A

Nothing, self assemble

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20
Q

The capsid can assemble how?

A
  1. Around nucleic acid

2. Form empty structure into which the nucleic acid is loaded

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21
Q

Capsids are resistant to what? 4

A
  1. drying
  2. acid
  3. detergents
  4. bile
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22
Q

Protein coat + nucleic acid inside = what?

A

Nucleocapsid

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23
Q

Do all viruses have lipid envelopes?

A

No, just some

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24
Q

The envelope is acquired how?

A

Host cell membrane through budding.

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25
Q

Envelopes are susceptible to what?

A

Organic solvents

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26
Q

Space between capsid and envelope is what?

A

Tegument

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27
Q

Viral glycoproteins and glycolipids insert into host where? 4

A
  1. PM
  2. NM
  3. ER
  4. Golgi
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28
Q

How does the virus localized capsid formation to appropriate location?

A

Viral matrix proteins associate with glycoproteins

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29
Q

A complete infectious virus particle is called what?

A

Virion

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30
Q

In naked viruses what is the virion?

A

Nucleocapsid

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31
Q

In enveloped viruses what is the virion?

A

Nucleocapsid + envelope

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32
Q

Which is more resitant, enveloped or naked viruses?

A

Naked viruses (act like endospore)

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33
Q

If a treatment can’t kill an endospore, will it kill a naked virus?

A

Probably not.

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34
Q

Are naked viruses as resistant as bacterial enzymes?

A

No, but close.

35
Q

If you take the envelope away from the enveloped virus, can it still infect?

A

no

36
Q

Are viral attachment proteins required for virus attachment

A

Yes

37
Q

Naked virus attachment proteins are where?

Where are the enveloped proteins?

A

In the nucleocapsid

In the membrane

38
Q

Viruses are grouped in what ways? 5

A
  1. nucleic acid type
  2. envelope presence
  3. Capsid symmetry
  4. organism that infect
  5. replication strategy
39
Q

What are viruses first classified by?
Then what?
Then what?

A

DNA vs RNA

Presence of envelope

Nature of the nucleic acid

40
Q

All negative strand RNA viruses have what feature?

A

Enveloped

41
Q

GI viruses are usually naked or enveloped?

A

Naked

42
Q

What are 9 steps of virus replication?

A
  1. Recognition
  2. Attachment
  3. Penetration
  4. Uncoating
  5. Transcription
    6 Protein synthesis
  6. Replication.
    8A: Envelopment
    8B: Assembly
  7. Budding and release
    9B. Lysis and release
43
Q

What is the main source of tissue tropism?

A

Virus recognition proteins for recognizing host cell surface

44
Q

In order to release capsid, what must enveloped viruses do?

A

Fuse envelope to membrane

45
Q

After attachment, what happens to non-enveloped viruses?

A

Taken into cell by receptor mediated endocytosis or direct penetration through viropexis

46
Q

Enveloped viruses do what to penetrate?

What is sometimes a requirement for this to happen?

A

Fuse with host cell membrane.

Correct acidity for the virus (neutral or acidic)

47
Q

Enveloped viruses can also form what during penetration?

A

Fuse neighboring cells into multinucleated giant cell

48
Q

After membrane fusion, what is the state of affairs?

A

Nucleocapsid is free in cytoplasm

49
Q

After internatlization where is the nucleocapsid sent?

A

Site of replication

50
Q

DNA viruses are sent where in the cell?

A

Nucleus

51
Q

RNA viruses are sent where in the cell?

A

Stay in cytoplasm

52
Q

One the virus is in the correct location, what happens?

A

Nucleic acid released from protein coat

53
Q

Which step is the most complicated?

A

Genomic replication and expression

54
Q

Critical step in genomic replication and expression is what?

A

Making mRNA

55
Q

With each virus what are the 3 genomic replication questions you must ask yourself?

A
  1. What enzyme is needed to replicate the genome?
  2. What enzyme is needed to express the genome
  3. Does a eukaryotic cell possess those enzymes?
56
Q

What are the 2 phases in the replication step for viruses?

A
  1. Early gene products made first: Viral polymerases and regulatory molecules
  2. Late gene products: structural proteins like capsid proteins
57
Q

What special things must a +ssRNA use to get translated?

A

Nothing, can be read by host ribosomes

58
Q

What special things must a -ssRNA use to get translated?

A

RNA-dependent RNA polymerase must be encoded on the virus in order to convert the negative strand to positive.

59
Q

Double stranded RNA must use what special things to get translated?

A

RNA-dependent RNA polymerase must be encoded on the virus.

60
Q

In order to replicate viral RNA, what is needed?

A

Negative strand templates

61
Q

Why do dsRNA need a viral polymerase for replication?

A

Hydrogen bonding between strands, need something that can separate them.

62
Q

How is genome replication in dsRNA described?

A

Completely conservative

63
Q

Retroviral +ssRNA must carry what for replication?

A

Reverse transcriptase: RNA dependent DNA polymerase

64
Q

In retroviral +ssRNA replication, what serves as the primer?

A

tRNA

65
Q

What does reverse transcriptase do?

A

Makes -ssDNA copy of mRNA

66
Q

The -ssDNA is converted to what in retroviral +ssRNA?

A

dsDNA in the nucleus.

67
Q

How is -ssRNA replicated?

A

Viral polymerase transcribes it to make mRNA, this is then used as template for more negative strand RNA

68
Q

What increases transcription of viral DNA?

A

Enhancers

69
Q

Is there an origin of replication in DNA virus replication?

A

Yes

70
Q

What provides the free 3’OH on DNA viruses? (2)

A
  1. Inverted repeats

2. Proteins with deoxycytidine monophosphate

71
Q

Which is faster, viral or host DNA polymerase?

Which has more errors?

A

Viral

Viral

72
Q

DNA viruses that use host DNA polymerase can only replicate where?

A

Actively dividing cells

73
Q

If a cell is at rest, can it replicate viral DNA?

A

No

74
Q

Translation of viral mRNA is done by what?

A

Host ribosomes

75
Q

Can viral mRNA’s be modified?

A

Yes, capped and poly-A-tail

76
Q

Viruses with a single nucleic acid particle usually encode what?

A

Polyproteins that are cleaved by proteases

77
Q

Viral mRNA translation is selected over host mRNA because? (3)

A
  1. Viral mRNA outnumbers host mRNA
  2. Blocking of cellular RNA from nucleus
  3. Inhibition of macromolecule synthesis and induced degradation of cellular DNA and RNA.
78
Q

Assembly of viruses begins when?

A

When viral pieces hit threshold for self assembly

79
Q

DNA viruses assemble where?

RNA viruses assemble where?

A

Nucleus

Cytoplasm

80
Q

Capsid proteins can assemble how? (2)

A
  1. around nucleic acid

2. loaded later

81
Q

Enveloped viruses acquire the lipid membrane when?
What is this process called?
Where can it occur? (3)

A

Release

Budding

NM, ER, Golgi

82
Q

Virions leave the cell in what manner? (6)

A
  1. lysis
  2. budding
  3. exocytosis
  4. bridge traversal
  5. Cell fusion
  6. vertical transmission
83
Q

what type of virus kills the cell upon release?

A

Naked

MICRO (22 decks)

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