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CMOD/PCM- Block 2 > Micro: Basics of Virology > Flashcards

Micro: Basics of Virology Flashcards

1
Q

T/F: Viruses are obligate intracellular parasites that replicate by self-assembly of individual components rather than by binary fission.

A

True

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2
Q

T/F: Viruses can make energy and proteins independent of a host cell.

A

False. Viruses CANNOT make these independent of a host cell.

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3
Q

T/F: Viruses contain a genome of limited size that contains both RNA and DNA.

A

False. Either RNA or DNA, but not both.

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4
Q

What is a virion?

A

A single virus particle.

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5
Q

List the 4 variations in viral genome structure (i.e. circular, linear, ds, ss…)

A

1) circular or linear single-stranded (ss) RNA
2) linear double-stranded (ds) RNA
3) linear ss DNA
4) circular or linear ds DNA

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6
Q

What is +RNA?

A

genomes that are the same sense as messenger RNA (mRNA)

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7
Q

What is -RNA?

A

genomes that are the OPPOSITE sense as mRNA

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8
Q

Some RNA viruses contain segmented genomes. What are these analogous to in eukaryotes?

A

effectively like several chromosomes within a single virion

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9
Q

In general, DNA genomes are larger or smaller than RNA genomes?

A

Larger

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10
Q

Virus genomes are packaged in protein shells known as:

A

Capsids

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11
Q

Are capsids malleable or rigid?

A

rigid

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12
Q

Capsids are the result of self-assembly of virally-encoded ________ .

A

capsomers

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13
Q

List the 3 forms of capsids.

A

helical
icosahedral (spherical)
complex

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14
Q

Is the shape of the capsid dictated by the shape of the genome or by the capsomers that self-assemble?

A

Capsomers

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15
Q

genome + capsid = ?

A

nucleocapsid = virion for “naked” viruses

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16
Q

A nucleocapsid surrounded by a lipid membrane is referred to as a virion for “______” viruses.

A

virion for “enveloped” viruses

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17
Q

What are inserted in the membrane of viruses and serve as virus attachment proteins and membrane fusion proteins?

A

Virally-encoded glycoproteins

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18
Q

Because the envelope of an “enveloped” virus is mostly lipid, enveloped viruses are more or less stable than “naked” viruses? Why?

A

Less stable. More susceptible to drying. Sensitive to detergents and alcohols. Cannot survive in the GI tract.

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19
Q

Which type (naked or enveloped) of virus spreads in large droplets, secretions, organ transplants, and blood transfusions?

A

enveloped viruses

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20
Q

Please list the 8 steps in viral replication.

A 
Attachment
Penetration
Uncoating
Early Transcription and synthesis of nonstructural proteins
Genome replication
Late transcription and synthesis of structural proteins
Assembly of virus particles
Release of virus particles
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21
Q

What are the two modes of penetration of viruses with their host cell?

A

endocytosis

membrane fusion

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22
Q

During the early transcription step of viral replication, do RNA viruses use host RNA polymerase?

A

No. Virally-encoded RNA-dependent RNA polymerase.

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23
Q

During the early transcription step of viral replication, do DNA viruses use host or self RNA polymerase?

A

Use host RNA polymerase (except poxoviruses)

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24
Q

Genome replication of RNA viruses occurs where in the host cell?

A

cytoplasm

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25
Q

Genome replication of DNA viruses occurs where in the host cell?

A

Nucleus (except poxoviruses and hepadnaviruses)

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26
Q

What causes the virions to be “released”?

A

host cell lysis or budding in the case of enveloped viruses.

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27
Q

List the 6 forms of viral cytopathogenesis.

A

1- inhibition of cellular protein synthesis
2- inhibition and degradation of cellular DNA
3- alteration of cell membrane structure
4- disruption of cytoskeleton
5- formation of inclusion bodies (typically represent sites of viral multiplication in a bacterium or a eukaryotic cell and usually consist of viral capsid proteins)
6- toxicity of virion components

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28
Q

T/F: +RNA virus genome functions as mRNA and is immediately translated by cellular ribosomes.

A

True

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29
Q

T/F: -RNA virus genome functions as mRNA and is immediately translated by cellular ribosomes.

A

False. -RNA virus genome CANNOT be used as mRNA; must be used as a template to transcribe a +RNA (mRNA) strand

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30
Q

Where does the RNA-dependent RNA polymerase come from that transcribes -RNA strands from the +RNA genome?

A

It is one of the individual proteins cleaved from the translated +RNA polyprotein

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31
Q

What are used as templates to make many copies of the +RNA genome?

A

-RNA strands

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32
Q

+RNA or -RNA copies are used as mRNA to make structural proteins and are encapsidated to produce nucleocapsids?

A

+RNA.

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33
Q

To transcribe the -RNA genome, the incoming virus particle carries a _______________ .

A

RNA-dependent RNA polymerase

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34
Q

What is the result of transcribing a -RNA strand?

A

A +RNA strand (mRNA)

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35
Q

Newly produced -RNA genomes are encapsidated to produce __________ .

A

nucleocapsids

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36
Q

Retrovirus particles carry an RNA-dependent _____ polymerase aka reverse transcriptase aka host genome hijacker aka Al-Qaeda of the Viral Realm.

A

RNA-dependent DNA polymerase

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37
Q

What does RNA-dependent DNA polymerase do, exactly?

A

+RNA genome is REVERSE TRANSCRIBED into dsDNA and integrated into the host genome. Then, retrovirus proteins and +RNA genome are transcribed by host enzymes. CRAZYYY

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38
Q

DNA virus (except poxvirus) genomes are transcribed by host ___________ .

A

host DNA-dependent RNA polymerases

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39
Q

T/F: Many viruses have a host shut-off mechanism that degrades host mRNAs.

A

True

40
Q

Many viruses use specific transcription factors that REDIRECT host polymerases to _____ genes and away from ______ genes.

A

viral; cellular (host)

41
Q

Viral genome replication is dependent on _______________ for LARGER viruses but smaller viruses use host DNA polymerase.

A

virally-encoded DNA-dependent DNA polymerase

42
Q

Newly produced DNA genomes are _______ to produce nucleocapsids.

A

Encapsidated

43
Q

When measuring viral growth in the lab, a plaque refers to what, exactly?

A

Many viruses lyse infected cells and the resulting “hole” in a confluent monolayer of cells is called a plaque

44
Q

What is a lysate?

A

The suspension of virions in culture medium that results from unrestricted growth of the virus on a cell monolayer.

45
Q

Are all virus particles produced in a lysate infectious?

A

Nope

46
Q

The ____________ measures the number of physical particles compared to the number of infectious virions.

A

particle-to-pfu (plaque forming unit) ratio

47
Q

________ measure the number of infectious virions in a given volume of lysate.

A

Plaque assays

48
Q

What is the basic unit of infectivity in a biological assay of virions.

A

plaque-forming units (pfu) per ml of lysate

49
Q

What is multiplicity of infection (MOI)?

A

the ratio of the number of infectious particles to the number of target cells to be infected

50
Q

An MOI of 1 will only infect about ___% of the cells in a monolayer.

A

60%

51
Q

An MOI of between ___ and ___ is needed to ensure that all the cells are infected.

A

5-10

52
Q

A single-cycle growth curve can be divided into two peroids:

A

Eclipse period and latent period

53
Q

Describe what is going on during the eclipse period of a single-cycle growth curve.

A

Post-penetration phase until virus can be detected intracellularly

54
Q

Which phases of the virus replication cycle are present in the eclipse period of the single-cycle growth curve?

A

Corresponds to uncoating, early transcription, and genome replication steps; ends at virus assembly.

55
Q

Describe what is going on during the latent period of a single-cycle growth curve.

A

post-penetration phase until virus can be detected extracellularly. Yes, includes the eclipse period.

56
Q

Which phases of the virus replication cycle are present in the latent period of the single-cycle growth curve?

A

Corresponds to uncoating, early transcription, genome replication, virus assembly, and release.

57
Q

Why do viral genome mutations occur at a relatively high frequency?

A

In part due to the large number of genome copies produced in ever infected cell. Also due to polymerase errors, especially for RNA viruses.

58
Q

What is complementation?

A

an exchange of proteins

59
Q

Briefly describe complementation.

A

If a genome with a lethal mutation in gene “X” arises along with the wild-type genome in the same cell, then the wild-type copy of the gene X can provide the function for the mutant genome. Mutant genome will be packaged into a capsid and will go on to infect a second cell upon release. However, the mutant will not be able to replicate in the second cell because its genome still contains the lethal mutation in gene X.

60
Q

What is recombination?

A

An exchange of genetic material on the same segment of genome

61
Q

How is recombination good for clearing mutations from a genome?

A

If a genome with a lethal mutation in gene X arises along with the wild-type genome in the same cell, then the mutation can be removed by recombination with the wild-type gene X. As a result, the virus will be able to replicate in a second cell because it now contains a wild-type genome.

62
Q

T/F: recombination occurs frequently with DNA viruses.

A

True

63
Q

Does true recombination occur with RNA viruses?

A

No, but they can exchange genetic material in a way that resembles recombination.

64
Q

What is reassortment?

A

An exchange of genetic material on different segments of genome

65
Q

Briefly describe the reassortment of genes and how it is significant to strain variation.

A

If two SEGMENTED viruses infect the same cell, they can exchange some of their segments at the time of virus assembly. As a result, a NOVEL strain of virus that is composed of segments from both of the “parents” can be released from the infected cell. Important mechanism for the generation of new influenza strains.

66
Q

What is the most common route of infection by viruses?

A

Inhalation

67
Q

Initial replication is in cells that express _____ receptors and contain appropriate cellular factors for replication.

A

viral receptors

68
Q

Localized spread of the virus can be achieved in two ways, describe them.

A

1- Release of virus from an infected cell and subsequent infection of surrounding cells.
2- Some enveloped viruses can fuse an infected cell with uninfected cells to directly spread to surrounding cells (syncytia formation). MIND BLOWN

69
Q

T/F: viruses may spread from the original site of infection by gaining access to the bloodstream or lymphatic system.

A

True

70
Q

What is viremia?

A

The presence of virions in the blood

71
Q

Viruses can gain access to the CNS by 3 mechanisms: circumventing the BBB, through CSF, or by direct uptake in ____________ .

A

circumventing the BBB
through CSF
direct uptake in peripheral nerves

72
Q

An incubation period of ______ is a short incubation period and is characteristic of viruses that do not require secondary spread for symptomology.

A

1-2 days

73
Q

_______ is usually the minimum incubation period for viruses that require secondary spread.

A

12-14 days

74
Q

Are patients infectious during the incubation period? (unknowingly spreading the virus to others)

A

They can be

75
Q

What is the acute phase of an infection?

A

The symptomatic phase of infection.

76
Q

Name and describe the 3 forms of persistent viral infection.

A

Chronic- virus is produced at low levels, but may not continue to cause disease symptoms (Hep B)
Latent- virus genome remains in cells indefinitely, but virus particles are not produced, except during reactivation (herpes)
Transforming- intact or partial virus genome integrates into cellular DNA or is otherwise maintained in the cell and immortalizes the cell, alters its growth properties (oncogenic)
a. RNA viruses: retroviruses, hep C virus
b. DNA viruses: hep B, papilloma virus, polyoma virus, adenovirus type 2, Epstein-Barr virus, human herpesvirus-8, pox

77
Q

Describe the first defense to viral infection by the immune system.

A

1- Nonspecific immune response, including NK cells and IFN
2- PRRs recognize viral PAMPs to induce IFN-alpha/beta
3- IFNs bind to surrounding, uninfected cells and induce pathways that prevent virus replication

78
Q

What is the main viral PAMP?

A

dsRNA

79
Q

Describe the 3 ways that IFNs induce surrounding uninfected cells to resist infection and thus prevent viral replication.

A

1) Protein kinase (PKR) pathway inactivates translation initiation factor eIF-2, inhibits viral protein translation.
2) 2-5A system activates RNase L which cleaves RNA, destroying RNA genomes or inhibiting viral transcription.
3) Mx pathway proteins are GTPases that inhibit RNA polymerase activity.

80
Q

List the 2 antigen-specific responses (cellular and humoral) that arise several days postinfection.

A

1) CD8+ T cells are the major cellular response to primal viral infections; infected cells are targeted for lysis through antigen presentation.
2) abs can neutralize virus binding or facilitate the lysis of enveloped viruses with complement.

81
Q

Explain why children defective in ab production are not more susceptible to viral infections.

A

This is due to the importance of cellular immunity compared to humoral immunity in fighting viral infection.

82
Q

List 4 ways that viruses evade immune defenses.

A 
1- antigen variation to escape humoral response 
2- inhibition of antigen presentation to escape cellular response
3- cytokine homologs that down regulate or block cellular response
4- latent infection in neurons where there is no class I MHC
83
Q

List the 3 types of antivirals

A

vaccines
immune globulin
drugs

84
Q

Under what viral conditions would a vaccine not be practical?

A

Many strains of the virus (serotypes) and if the virus undergoes much antigenic variation due to high mutation rates in a dominant antigenic structure

85
Q

List the 3 basic types of viral vaccines.

A

1- live, attenuated virus
2- killed virus
3- subunit (recombinant DNA)

86
Q

Do attenuated vaccine strains produce symptoms?

A

Yes, subclinical infections

87
Q

What are the advantages of attenuated vaccines?

A 
cheap
Strong response (IgG, IgA, T cell) that is long lasting
88
Q

What are the disadvantages of giving an attenuated vaccine?

A

can be labile in transport
cannot be given to immunocompromised pts
can revert to virulence in rare cases

89
Q

Can a killed virus cause illness?

A

No

90
Q

What are the advantages of a killed virus vaccine?

A

very stable
rare side effects
cannot revert to virulence

91
Q

What are the disadvantages of a killed virus vaccine?

A

expensive to prepare

shorter term immunity that is mostly limited to IgG

92
Q

Subunit vaccines exist for which two virus families?

A

Hep B and HPV

93
Q

What are subunit vaccines, anyway?

A

Composed of single viral proteins that are expressed in yeast using recombinant DNA technology.

94
Q

What are the advantages and disadvantages of subunit vaccines?

A

ADV:
cannot cause disease
are not derived from blood

DisADV:
requires multiple injections

95
Q

T/F: immune globulin is used in both pre- and post exposure prophylaxis.

A

True

CMOD/PCM- Block 2 (41 decks)

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