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Micro unit 2 > L1 > Flashcards

L1 Flashcards

1
Q

Dimitri Ivanofsky showed that Tobacco Mosaic Virus (TMV) was able to

A

pass through a filter while bacteria could not (1892)

First electron micrograph of TMV in 1939

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2
Q

Martinus Beijerinck showed that the titer of TMV

A

increased after infecting a plant, proving TMV was not a toxin (1898)

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3
Q 
Bacteria viruses (bacteriophage)
 discovered by
A

Frederick W. Twort (1915) while trying to grow vaccinia virus

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4
Q

Bacteriophage were instrumental in developing the field of

A

virology and expanding the field of biology

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5
Q

Foot and mouth disease

A

first animal virus) discovered (1898)

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6
Q

Yellow fever virus

A

(first human virus) discovered in 1901

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7
Q

Viruses are

A

obligate intracellular parasites

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8
Q

Viruses are not

A

autopoietic

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9
Q

Cellular origin

A

Proposes that viruses were once cellular components but over time they evolved separately.

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10
Q

Autopoietic origin

A

Proposes that viruses, once autopoietic entities, became dependent on cells for replication.

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11
Q

Attributes for Virus Classification

A 
Virus particle structure
Genome
Replication features
Serology
Stability
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12
Q

Nucleocapsid

A

RNA or DNA in a core that is protected by a protein coat (capsid)

Virus is defined by the nucleocapsid structure

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13
Q

Nucleocapsid structural symmetry

A

helical
pelomorphic
Icosahedral

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14
Q

Nucleocapsid is comprised of repeating

A

protein subunits called capsomeres

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15
Q

Envelopes:

A

virus-modified cellular membranes acquired upon exit from host

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16
Q

Exposure to lipid solvents in the laboratory (e.g., alcohol, ether, acetone, Freon, etc.) renders enveloped viruses

A

noninfectious

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17
Q

Enveloped viruses may have nucleocapsids with

A

different structures

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18
Q

Smallest virus

A

18 nm

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19
Q

Largest

A

300 nm

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20
Q

Virus Genome DNA

A

double or single stranded

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21
Q

Virus genome RNA

A 
RNA
Double stranded
Single stranded
Plus sense (+)ssRNA
Minus sense (-)ssRNA (polarity)
Ambisense
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22
Q

Ambisense

A

Among the negative RNA viruses, ambisense RNA viruses or ‘ambisense viruses’ occupy a distinct niche. Ambisense viruses contain at least one ambisense RNA segment, i.e. an RNA that is in part of positive and in part of negative polarity.

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23
Q

Virus Genome Structure

A 
Linear
Circular
Segmented
Diploid
Gene arrangement can change this
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24
Q

Virus Replication steps

A 
Attachment
Entry
Transcription
Translation
Replication
Assembly
Release
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25
Q

Viral attachment is the

A

Binding of a virus receptor to a cellular receptor

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26
Q

Cellular receptors

A

Signaling molecules – induced cellular response to binding
Cell adhesion
Transport

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27
Q

Viral receptors usually do not

A

mimic cell receptor’s normal ligands

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28
Q

viral receptors typically are

A

Typically are spike like projections on particle surface

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29
Q

Viral creceptor smay require

A

a co-receptor- e.g., HIV (CD4, CXCR4)

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30
Q

Genetic engineering - can change receptor recognition

A

Integrin RGD sequence – used by Ad, engineered into lambdaphage
Pseudotyping particles – improve retroviral entry, VSV, Ebola, LCMV

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31
Q

Attachment is a major determinant of

A

virus tropism (host range)

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32
Q

Viruses infect essentially all known

A

forms of life
Specific host ranges, some can infect humans and animals (zoonosis)
Not shared across more divergent hosts (plants, bacteriae

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33
Q

Virus Replication – Entry - Pathways

A

Receptor rrrr3 mediated endocytosis

Direct penetration of plasma membrane

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34
Q

Enveloped virus

- viral entry

A

Membrane fusion
Best understood for influenza
HA protein – attachment & fusion

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35
Q

Receptor conformational change

Receptor conformational change

A

Low pH

Receptor induced

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36
Q

3Uncoating

A

involves nuclear replication nd cytoplasmic replication after uncoating

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37
Q

Nuclear replication

A

Genome and remaining protein coat (nucleocapsid) transported to the nuclear membrane
Delivery of genome to nucleus

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38
Q

Cytoplasmic replication

A

Release of the genome in cytoplasm
Transportation of the genome to intracellular site of replication
Many RNA viruses replicate in membrane associated complexes

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39
Q

dsRNA viruses never release their

A

genomic material from the entering particle

40
Q

DNA viruses usually rely upon cellular

A

RNA polymerases

41
Q

The genome of (+)ssRNA viruses can

A

serve as mRNA

Production of new transcripts can occur later using a (-)ssRNA template

42
Q

(-)ssRNA, dsRNA viruses must bring their own

A

polymerase into the cell

43
Q

All viruses need the cell’s

A

ribosomes to produce protein – no exceptions

44
Q

Viral protein production can be regulated at the

A

transcript (mRNA) level or translation level

45
Q

Structural proteins are produced in

A

high quantities

46
Q

Non-structural proteins are only seen inside the

A

infected cell

47
Q

(+)ssRNA Genome serves as template for

A

translation

48
Q

(+)ssRNA

-Polymerase makes (-)ssRNA copy as

A

template for new genomes

49
Q

(-)ssRNA

Virus particle must include the

A

viral polymerase

50
Q

-ssrna Polymerase makes

A

messenger RNA for translation

51
Q

Viral Genome replicates through full-length

A

(+)ssRNA intermediate

52
Q

dsRNA

A

Virus particle includes viral polymerase

53
Q

dsRNA induces innate

A

immune response so genome stays inside particle

54
Q

mRNA synthesized in particle and exported to

A

cytoplasm

55
Q

mRNA serves as

A

(+) strand in virus genome, (-) strand synthesized during assembly

56
Q

ssDNA and dsDNA must gain access to

A

nucleus

57
Q

Poxviruses are an exception, virion contains the necessary

A

RNA polymerase and the genome encodes the DNA polymerase for replication

58
Q

ssDNA and dsDNA Prepare the cell for

A

DNA replication
Growth phase, dNTP production, replication machinery
Ensure genome ends are copied

59
Q

ssDNA and dsDNA Prepare the cell for

A

DNA replication
Growth phase, dNTP production, replication machinery
Ensure genome ends are copied

60
Q

Virus assembly

A

Package new genomes into functional particles
Localize structural proteins to aid assembly
Cellular viral “factories”

61
Q

Virus Genome contains

A

packaging signals

62
Q

Adenovirus –

A

empty protein coat imports genome

63
Q

Reovirus –

A

RNA packaged during capsid assembly

64
Q

Retrovirus –

A

preassembly on a membrane

65
Q

Lysis

A

Best known for bacteriophage

Viral molecules that rupture cellular membrane

66
Q

Weak Lysis

A

Depends on membrane breakdown after cell death

67
Q

Budding (enveloped only)

A

Enveloped viruses use cell membrane as the outer coat of the virus particle

68
Q

One step growth curve

A

Infect every cell at same time (MOI > 5)

Every cell dies at end of infection

69
Q

Phases

A

Eclipse
Exponential growth
Plateau

70
Q

Eclipse:

A

attachment and uptake

71
Q

Exponential growth:

A

replication and assembly

72
Q

Plateau:

A

cell death

73
Q

Virus Replication - Kinetics Useful to assess:

A

Mutations
Cell entry
Process design

74
Q

Time for one step growth

A

Start of infection to beginning of plateau
Bacteriophage – 30 min
Vesicular stomatitis virus (VSV): 6 hours
Vaccinia: 24 hours

75
Q

Productivity

A

Measure amplification
VSV – 1:1000
Vaccinia – 1:100

76
Q

Initial discovery

A

Disease in a host

Contaminant in cell culture

77
Q

Confirmation

A

Purification of virus
Confirmation of disease
Animals, eggs or cell culture
Cell culture is preferred

78
Q

Principle of Detection and Quantification Methods

A

Infectivity
Physical
Genome
Serological

79
Q 
Cytopathic Effect (CPE)
 infection assay
A

Cell Rounding
Syncytia Formation
Inclusion bodies

80
Q

Fluorescent Focus Assay

infection assay

A

Infect cells
Expose virus antigen
Stain with labeled antibody
Count areas that fluoresce

81
Q

Plaque Assay

infection assay

A

Cell monolayer
Inoculate with dilute virus
Infected cells die leaving a clear area – plaque

82
Q

Infectious Dose

infection assay

A

ID50, IU50, TCID50
Systems: Tissue Culture, Eggs, Animals
Inoculate with different dilutions of virus
Calculate concentration based on number infected

83
Q

Particle Assays

A

Electron microscopy

Hemagglutinin assay

84
Q

Electron microscopy

A

Direct image of virus particles

Calibrate with latex bead standard

85
Q

Hemagglutinin assay

A

Viruses that bind red blood cells (RBCs)
Mix constant number of RBCs with various virus dilutions
If virus concentration is sufficient, a matrix of RBCs and virus is formed
Matrix does not allow RBCs to pellet

86
Q

Polymerase Chain Reaction

genome assay

A

DNA primer specific to virus
Amplify the gene
Very sensitive

87
Q

Southern (DNA) & Northern (RNA) Blots

genome assay

A

Isolate DNA or RNA
Separate by electrophoresis
Use labeled DNA probe to detect

88
Q

Serological Assays

A

Virus neutralization
Enzyme Link Immunosorbant Assay (ELISA)
Western (Protein) Blot

89
Q

Virus neutralization

A

Antibody binding to virus can block infection

Virus concentration determined by amount of antibody needed

90
Q

Enzyme Link Immunosorbant Assay (ELISA)

A

Antibody recognition of virus

Amplification by enzyme linked to antibody

91
Q

Western (Protein) Blot

A

Separate proteins by electrophoresis

Probe proteins using an antibody

92
Q

Viruses are obligate

A

intracellular parasites; use host cell’s replication processes to duplicate themselves

93
Q

Every virus has a

A

nucleocapsid consisting of genetic material (RNA or DNA) and protein; some viruses are enveloped (coated with a host cell membrane)

94
Q

Human viruses have diameters of

A

30-300 nm

95
Q

Viruses are classified by the

A

genome, virus particle structure, and replication strategy

96
Q

RNA viruses replicate in

A

cytoplasm

97
Q

DNA viruses replicate in

A

nucleus

Micro unit 2 (12 decks)

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