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Module 9 - Viruses Flashcards

1
Q

What are viruses?

A

Small particles that can replicate inside living host cells

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2
Q

How are viruses obligate intracellular parasites?

A

They rely on taking over the host cell to function

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3
Q

True or false: viruses can infect all forms of life

A

True

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4
Q

How many viruses exist on the planet?

A

Millions

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5
Q

How many viruses have been extensively characterized?

A

5000

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6
Q

How long have viruses plagues humans?

A

Since before we knew about them

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7
Q

How old is the history of virology?

A

Nearly as old as the history of life itself

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8
Q

What is virus Latin for?

A

Poison

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9
Q

When was yellow fever virus discovered?

A

1901

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10
Q

What did Walter Reed do?

A

Showed yellow fever was causes by a virus transmitted by mosquitos in 1901

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11
Q

Who discovered yellow fever virus?

A

Walter Reed

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12
Q

What did Stanley (from Columbia) do?

A

Crystallized TMV

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13
Q

When was TMV crystallized?

A

1935

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14
Q

Who crystallized TMB?

A

Stanley (from Columbia)

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15
Q

How was TMV isolated?

A

In a filtered, bacteria-free fluid

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16
Q

What is the typical size of a virus?

A

10-100 nm

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17
Q

What is the typical genome size of a virus?

A

A few thousand to 200,000 nucleotides

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18
Q

How many genetic molecules do viruses typically have?

A

One

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19
Q

How can viruses have more than one genetic molecule?

A

By having a segmented genome

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20
Q

What is the structure of the genetic material in viruses?

A

Linear or circular, single or double stranded DNA or RNA

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21
Q

What is the host for poliovirus?

A

Humans

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22
Q

What is the structure of poliovirus?

A

Non-enveloped, icosahedral

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23
Q

What is the size of poliovirus?

A

30 nm

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24
Q

What is the genome size of poliovirus?

A

7.7 kbp

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25
Q

What is the genetic material of poliovirus?

A

ssRNA

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26
Q

What is the host for TMV?

A

Tobacco and related plants

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27
Q

What is the structure of TMV?

A

Non-enveloped, helical

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28
Q

What is the size of TMV?

A

300x18 nm

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29
Q

What is the genome size of TMV?

A

6.4 kbp

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30
Q

What is the genetic material of TMV?

A

ssRNA

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31
Q

What does TMV stand for?

A

Tobacco mosaic virus

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32
Q

What is the host of T4?

A

E. coli

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33
Q

What is the structure of T4?

A

Non-enveloped

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34
Q

What is the size of T4?

A

200x90 nm

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35
Q

What is the genome size of T4?

A

170 kbp

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36
Q

What is the genetic material of T4?

A

dsDNA

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37
Q

What is the host for variola virus?

A

Humans

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38
Q

What is the structure of variola virus?

A

Enveloped, complex

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39
Q

What is the size of variola virus?

A

300x250 nm

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40
Q

What is the genome size of variola virus?

A

186 kbp

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41
Q

What is the genetic material of variola virus?

A

dsDNA

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42
Q

What is the most for mimivirus?

A

Amoeba

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43
Q

What is the structure of mimivirus?

A

Enveloped, complex

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44
Q

What is the size of mimivirus?

A

400 nm

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45
Q

What is the genome size of mimivirus?

A

1200 kbp

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46
Q

What is the genetic material of mimivirus?

A

dsDNA

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47
Q

What surrounds the viral genome?

A

A capsid

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48
Q

What is a capsid?

A

Viral proteins that surround the viral genome

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49
Q

What are capsids composed of?

A

Capsomeres

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50
Q

What is a capsomere?

A

A subunit of a capsid

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51
Q

What is a capsomere composed of?

A

One or more polypeptides

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52
Q

What are the common shapes of a capsid?

A

Helical or icosahedral

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53
Q

What type of genome do helical viruses have?

A

ssRNA

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54
Q

What are some examples of helical viruses?

A

Ebola, TMV

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55
Q

What are some examples of icosahedral viruses?

A

Rhinovirus, adenovirus, poliovirus

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56
Q

What does rhinovirus do?

A

Causes the common cold

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57
Q

True or false: capsid shapes are always simple

A

False: they can have irregular or complex shapes

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58
Q

What is the typical structure of bacterial viruses?

A

Icosahedral head and a helical tail

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59
Q

What do the tail fibers do in bacteriophages?

A

Help binding to host cells

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60
Q

What is the nucleocapsid?

A

The capsid and genome of the virus

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61
Q

What is an enveloped virus?

A

A virus where a plasma membrane surrounds the nucleocapsid

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62
Q

What is a naked virus?

A

A virus where there is no plasma membrane surrounding the nucleocapsid

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63
Q

What is another name for a naked virus?

A

A non-enveloped virus

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64
Q

What are some examples of enveloped viruses?

A

Influenza and HIV

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65
Q

What are spikes?

A

Glycoproteins inserted into the lipid membrane of enveloped viruses

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66
Q

What are some examples of spike proteins?

A

Hemagglutinin and neuraminidase

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67
Q

Which virus has hemagglutinin and neuraminidase?

A

Influenza

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68
Q

What does hemagglutinin and neuraminidase determine?

A

Subtype of influenza

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69
Q

What are the 4 steps for viral replication?

A
  1. Adhere
  2. Penetrate and uncoat
  3. Synthesis
  4. Assembly and exit
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70
Q

What happens when a virus sticks to the host cell?

A

It releases its genome into the cell

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71
Q

What happens once the viral genome is inside the host cell?

A

The host cell expresses the genes to make proteins, replicate genome, and put itself together

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72
Q

What is the most important part of the viral replication cycle?

A

Entry into the host cell

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73
Q

What does the entry mechanisms depend on?

A

The host cell

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74
Q

How are animal cell viruses different from bacterial, plant, and fungal viruses?

A

Animal viruses do not have to contend with cell wall, while bacterial, plant, and fungal viruses do

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75
Q

What does entry of viruses into plant cells depend on?

A

Some damage on the plant tissue

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76
Q

Why do plant viruses rely on plant tissue damage?

A

It opens a spot on the cell wall

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77
Q

How can plant tissue be damaged?

A

Through insects feeding on plants, wind damage, hail/rail damage, fire damage, or human-induced damage

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78
Q

True or false: bacterial viruses enter the host cell

A

False: they do not enter the host cell after attachment

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79
Q

What happens when bacterial viruses attach to the host cell?

A

There is a conformational change in the tail protein subunits, which moves DNA from capsid head into bacterial cytoplasm

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80
Q

What happens when animal viruses attach to the host cell?

A

Some form of virion capsid or viral genome enters the cytoplasm

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81
Q

How do non-enveloped animal viruses enter the cell?

A

The entire viral particle enters through endocytosis

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82
Q

How do enveloped viruses such as HIV enter the cell?

A

They undergo a membrane fusion event at the cell surface

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83
Q

How do enveloped viruses such as influenza enter the cell?

A

They first enter through endocytosis, and then the viral capsid undergoes a specific set of disassembly to release the genome into the cytoplasm

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84
Q

What is the consequence of viruses only being able to replicate within living host cells (in terms of evolution)?

A

Their origin must be connected with the host cell

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85
Q

What three hypotheses have been proposed for the origin of viruses?

A

Coevolution, regressive, and progressive

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86
Q

What is another name for the coevolution hypothesis?

A

The virus first hypothesis

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87
Q

What does the coevolution hypothesis state?

A

Viruses co-evolved with current cellular hosts, or existed before cells

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88
Q

What are the strengths of the coevolution hypothesis?

A

It can explain the origin of many RNA viruses

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89
Q

What are the weaknesses of the coevolution hypothesis?

A

It has little support outside of RNA viruses

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90
Q

What does the regressive hypothesis state?

A

Viruses were cells that lost their metabolic and replicative features over time, thus depending on the host cell

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91
Q

What are the strengths of the regressive hypothesis?

A

There is support from nucleocytoplasmic large DNA viruses

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92
Q

What are the weaknesses of the regressive hypothesis?

A

It does not explain the origin of RNA viruses

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93
Q

What does the progressive hypothesis state?

A

Existing genetic elements gradually gained the ability to move between cells

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94
Q

What are the strengths of the progressive hypothesis?

A

There is evidence in the similarity of replication of retroviruses and replication of transposons and retrotransposons

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95
Q

Based on the progressive hypothesis, how did retroviruses evolve?

A

From eukaryal retrotransposons

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96
Q

How do transposons move within a genome?

A

By converting DNA to RNA, and then converting back into DNA

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97
Q

How is RNA converted into DNA for transposons?

A

Through the enzyme reverse transcriptase

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98
Q

What is done with the DNA copy produced by reverse transcriptase in transposons?

A

It can be integrated into a different location on the chromosome

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99
Q

How are retroviruses similar to retrotransposons?

A

They also undergo RNA to DNA conversion, and they have a similar genetic organization

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100
Q

True or false: there is evidence for all three hypothesis of viral origin

A

True: each of them has different evidence

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101
Q

True or false: one hypothesis of viral origin completely explains the origin of viruses

A

False: each of them have a partial description

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102
Q

What traits of viruses makes them difficult to work with?

A

They are small and can only replicate within appropriate host cells

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103
Q

What is needed to cultivate viruses?

A

Host cells must be inoculated with virus, and progeny viruses must be harvested

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104
Q

How are bacteriophages cultivated?

A

A culture of actively growing bacteria are inoculated with a small sample of phage

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105
Q

How can a researcher tell that a bacteriophage is replicating?

A

The growth media changes from turbid to clear

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106
Q

What happens after incubation of bacteriophages?

A

The medium is centrifuged, and the resulting supernatant is filtered

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107
Q

What is done to isolate a viral clone?

A

Molten nutrient agar is added to the cells and poured on a plate

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108
Q

What is the purpose of the molten nutrient agar?

A

It inhibits free movement of virus

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109
Q

What does a virus produce when plated?

A

A visible plaque of dead cells

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110
Q

What does each discrete plaque represent?

A

A clone (the progeny of a single virus)

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111
Q

What is done to cultivate animal viruses?

A

A small amount of virus is added to host cells growing in a flask

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112
Q

What do the viruses in the animal cell flask do?

A

New viral particles are released from infected cells into the medium, and infect other cells

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113
Q

What does the replication of many animal viruses lead to?

A

CPEs

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114
Q

What is an example of a virus that produces CPEs?

A

Poliovirus

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115
Q

What does CPE stand for?

A

Cytopathic effects

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116
Q

What are CPEs?

A

Visible changes in cellular morphology

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117
Q

What are CPEs often associated with?

A

Cell damage or death

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118
Q

What are CPEs commonly used as a marker for?

A

Extent of viral replication

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119
Q

What cell line was used to develop the tools to study animal viruses?

A

HeLa cells

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120
Q

What is done for simple and relatively crude purifications?

A

A viral suspension can be centrifuged and filtered through a very small pore filter

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121
Q

What does differential centrifugation do?

A

Separates particles by mass

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122
Q

What does low speed centrifugation lead to?

A

Pelleting of large objects, including cells

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123
Q

What does high speed centrifugation lead to?

A

Pelleting of small objects, such as viruses

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124
Q

What does gradient centrifugation do?

A

Separates particles by density (concentration)

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125
Q

What is the setup for gradient centrifugation?

A

The sample is layered on top of a density gradient made up of sucrose concentrations (ranging from 20-70%)

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126
Q

How does gradient centrifugation work?

A

During centrifugation, particles move down until they encounter a sucrose concentration equivalent to particle density

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127
Q

What is the product of gradient centrifugation?

A

Bands at different locations in the tube

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128
Q

What is the product of differential centrifugation?

A

Pellets and supernatant

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129
Q

What are the 4 methods used to quantify viruses?

A

Direct count, hemagglutination assay, plaque assay, and endpoint assay

130
Q

How does direct count work?

A

The absolute number of total viral particles is calculated with an electron microscope

131
Q

What are the disadvantages of the direct count method?

A

It requires an expensive, specialized microscope, and it does not differentiate between infectious and non-infectious viral particles

132
Q

What does the hemagglutination assay rely on?

A

The properties of some viruses to stick to RBCs, forming a gel mat

133
Q

What does RBC stand for?

A

Red blood cell

134
Q

True or false: hemagglutination assay can be done on all viruses

A

False: it can only be done on certain viruses

135
Q

What is hemagglutionation?

A

The process of RBCs clumping up together due to viruses binding to the RBC surface

136
Q

True or false: hemagglutination can be seen with the naked eye

A

True: no microscope is required

137
Q

What are the advantages of the hemagglutination assay?

A

It is cheap, easy, fast, and requires no microscope

138
Q

What are the disadvantages of the hemagglutination assay?

A

It cannot differentiate between viable and non-viable viruses, and there is no virus number

139
Q

What type of viruses is the plaque assay useful for?

A

Phages and plant viruses

140
Q

What is the plaque assay commonly used for?

A

To determine infectious titer

141
Q

What are the steps of a plaque assay?

A
  1. A series of dishes with host cells are inoculated with serial dilutions of the virus
  2. Newly formed viruses infect neighboring cells, resulting in plaques
  3. Plaques are counted to determine PFU
142
Q

What is a plaque?

A

A collection of dead cells

143
Q

What does PFU stand for?

A

Plaque forming unit

144
Q

What is the endpoint assay used for?

A

Determining the TCID50

145
Q

What does TCID50 stand for?

A

Tissue culture infectious dose 50

146
Q

What are the steps of an endpoint assay?

A
  1. Dilutions of viruses are used to infect cells in a growing culture
  2. Cells are monitored for CPEs, and calculated to find out how much viruses is needed to cause CPE 50% of the time
147
Q

How is the TCID50 calculated from the endpoint assay?

A

The number of viruses needed to cause CPE 50% of the time is calculated

148
Q

How can viruses be named?

A

Based on the location of discovery, the disease they cause, or appearance

149
Q

What are some examples of viruses named based on a location?

A

Ebola, West Nile

150
Q

What are some examples of viruses named based on diseases?

A

TMV, Hepatitis A

151
Q

What are some examples of viruses named based on a physical characteristic?

A

Coronavirus, Picornaviridae

152
Q

What are some notes about Ebola virus?

A
  1. First recognized outbreak occurred in Zaire (Democratic Republic of Congo) near Ebola River
  2. Most subsequent outbreaks occurred in central Africa
153
Q

What are some notes about West Nile virus?

A
  1. Initially isolated from a person living near Nile River in Uganda
  2. First appeared in USA in 1999, now firmly established in North America
154
Q

What are some notes about TMV?

A
  1. Plant infected show distinct discoloration, or mosaic pattern
  2. First described in 1880s, still causes significant crop loss today
155
Q

What are some notes about Hepatitis A virus?

A
  1. A number of viruses (A, B, C) have been identified

2. All cause damage to liver cells, but differ significantly from each other

156
Q

What are some notes about coronaviruses?

A
  1. Have projections on surface that resemble crowns or coronas
157
Q

What are some notes about picoronaviruses?

A
  1. Have very small (pico) RNA genomes
158
Q

What does ICTV stand for?

A

International Committee on Taxonomy of Viruses

159
Q

Based on the ICTV, how are viruses classified?

A

Based on order, family, subfamily, genus, and species

160
Q

What can be used as a common feature to compare viruses?

A

How they form mRNA

161
Q

How come mRNA can be used as a common feature to compare viruses?

A

Because all viruses make mRNA recognized by ribosomes of host cells

162
Q

How does the Baltimore classification system work?

A

Each virus is divided into 7 classes based on how they make mRNA

163
Q

What did David Baltimore do?

A

Develop the Baltimore system of classification

164
Q

What is a class I virus?

A

dsDNA genome

165
Q

What is an example of a class I virus?

A

Human herpesvirus

166
Q

What is a class II virus?

A

ssDNA genome

167
Q

What is an example of a class II virus?

A

Parvoviruses

168
Q

What is a class III virus?

A

dsRNA genome

169
Q

What is an example of a class III virus?

A

Reoviruses

170
Q

What is a class IV virus?

A

ssRNA genome, positive sense

171
Q

What is an example of a class IV virus?

A

Poliovirus

172
Q

What is a class V virus?

A

ssRNA genome, negative sense

173
Q

What is an example of a class V virus?

A

Influenza virus

174
Q

What is a class VI virus?

A

ssRNA genome, DNA intermediate

175
Q

What is an example of a class VI virus?

176
Q

What is a class VII virus?

A

ssRNA genome, RNA intermediate

177
Q

What is an example of a class VII virus?

A

Hepatitis B virus

178
Q

What class of virus has a dsDNA genome?

179
Q

What type of virus is human herpesvirus?

180
Q

What class of virus has a ssDNA genome?

181
Q

What type of virus is parvovirus?

182
Q

What class of virus has a dsRNA genome?

183
Q

What type of virus is reovirus?

184
Q

What class of virus has a ssRNA genome, positive sense?

185
Q

What type of virus is poliovirus?

186
Q

What class of virus has a ssRNA genome, negative sense?

187
Q

What type of virus is influenza?

188
Q

What class of virus has a ssRNA genome, DNA intermediate?

189
Q

What type of virus is HIV?

190
Q

What class of virus has a dsDNA genome, RNA intermediate?

191
Q

What type of virus is hepatitis B?

192
Q

How is electron microscopy used in virology?

A

It is useful to see physical differences or how they look like

193
Q

How is nucleic acid analysis used in virology?

A

It provides more exact information about virus identity

194
Q

How is rtPCR different from PCR?

A

rtPCR uses reverse transcriptase to create cDNA from mRNA, which can then undergo the PCR reaction

195
Q

What is needed for rtPCR?

A

Primers, Taq polymerase, nucleotides, and reverse transcriptase

196
Q

When were viroids first isolated?

197
Q

How were viroids first discovered?

A

As infectious agents that caused potatoes to grow abnormally

198
Q

What do viroids do?

A

Infect plants

199
Q

What is the structure of a viroid?

A

Naked circular ssRNA, with a complicated secondary structure

200
Q

How do viroids achieve intricate secondary structure?

A

Through intracellular complementary base pairing

201
Q

How large is a typical viroid?

A

400 nucleotides

202
Q

What is the purpose of the extensive secondary structure of viroids?

A

It makes it resistant to ribonucleases

203
Q

What do satellite viruses and satellite RNAs do?

A

Infect plants

204
Q

What do satellite viruses and satellite RNAs have in common?

A

They both have small RNA genomes

205
Q

How do satellite viruses and satellite RNAs replicate in hosts?

A

They require a helper virus that co-infects the host cell for replication

206
Q

Where do satellite viruses get the capsid protein?

A

From their own gene

207
Q

Where do satellite viruses get the capsid protein?

A

From the helper virus

208
Q

What is an example of a satellite virus?

209
Q

What does HDV stand for?

A

Hepatitis D virus

210
Q

What is needed for HDV to infect a cell?

A

HBV also needs to infect the cell for HDV to replicate

211
Q

True or false: HDV has an envelope

A

True: it is an enveloped virus

212
Q

What do prions stand for?

A

Proteinaceous infectious particles

213
Q

What is the structure of a prion?

A

Just protein (no DNA or RNA)

214
Q

How are prions infectious agents?

A

They can replicate in the host and cause diseases

215
Q

What are some specific diseases caused by prions?

A

Kuru in humans, Scrapie in sheep, mad cow disease in cattle

216
Q

What types of dieases are caused by prions?

217
Q

What does TSE stand for?

A

Transmissible spongiform encephalopathies

218
Q

What are TSEs?

A

A group of progressive neurological diseases

219
Q

What are prions?

A

Misshapen forms of naturally occurring proteins

220
Q

Where do the prion proteins normally exist?

A

On the surface of the neuron

221
Q

What are the two states of the prion protein?

A

The more common cellular form, or the pathogenic scrapie form

222
Q

What happens when pathogenic proteins come in contact with the normal cellular proteins?

A

It causes the cellular molecule to change shape and become pathogenic

223
Q

What is the consequence of the prion causing a normal protein to change shape?

A

It can replicate and function as an infectious agent

224
Q

What can make the prion protein more likely to assume the pathogenic confirmation?

A

Certain mutations in the gene

225
Q

True or false: prion-associated diseases can be both infectious or genetic

A

True: it can arise from another source, or from genetics

226
Q

What is thought to lead to disease from prions?

A

The formation of fibrils

227
Q

How have viruses shaped human history?

A

Smallpox decimated Native American populations, and influenza influenced the outcome of World War I

228
Q

What did Dimitri Ivanovski do?

A

Demonstrated a disease in tobacco plants (TMV) that could be transmitted after using a filter in 1892

229
Q

What is the official beginning of virology?

A

Martinus Beijerinck describing TMV as contagium vivum fluidum (soluble living germ) in 1898

230
Q

What did Frederick Twort and Felix d’Herelle do?

A

Described bacteriophages in the early twentieth century

231
Q

What does variola virus do?

A

It is the agent of smallpox

232
Q

What is an example of a virus with a segmented genome?

A

Influenza virus A

233
Q

How does influenza virus A have a segmented genome?

A

It has eight segments of ssRNA that code for ten different proteins

234
Q

What are the largest viruses (in terms of size)?

A
  1. Pithovirus sibericum (1.5 um x 500 nm)

2. Mimivirus (400 nm)

235
Q

What are the largest viruses (in terms of genome)?

A
  1. Pandoravirus salinus (2.47 Mbp)
  2. Megavirus chilensis (1.2 Mbp)
  3. Mimivirus (1.2 Mbp)
236
Q

What genes are found in large viruses (such as mimivirus)?

A

Genes similar to synthesis of nucleotides and amino acids

237
Q

What is the structure of influenza virus?

A

Multiple copies of the NP (nucleoprotein) and viral polymerase complex associate with each segment of RNA

238
Q

What does helical symmetry lead to?

A

Filamentous, fiber-like, or rod shaped morphology

239
Q

What is a virion?

A

Complete viral particle

240
Q

What is the virion in helical plant and bacterial viruses?

A

The entire helical nucleocapsid

241
Q

What do all known animal viruses with helical symmetry have?

A

An envelope

242
Q

What does the genome size of a helical virus determine?

A

How large it is (capsid can grow indefinitely)

243
Q

How come the genome size of an icosahedral virus is limited?

A

Only a certain amount of genetic material can be packaged inside the capsid

244
Q

What is the purpose of a viral envelope?

A

The associated proteins are important for successful entry into the cell

245
Q

How many protein units are used for an icosahedral capsid?

A

60 (3 polypeptides x 20 faces)

246
Q

What is the advantage of a viral envelope?

A

It can disguise the virus from the host cell immunity, and helps with attachment

247
Q

What is the disadvantage of a viral envelope?

A

The envelope is typically degraded in external environment through desiccation and exposure to chemicals

248
Q

What is an attachment protein, and what does it do?

A

It is a protein on the surface of the virus that aids in binding to a host cell

249
Q

How does adenovirus interact with receptors?

A

A spike protruding from the vertices

250
Q

How does poliovirus interact with receptors?

A

Through amino acid residues in an indentation within the capsid

251
Q

What receptors does HIV use?

A

CD4, CCR5, and CXCR4

252
Q

What breaks down the influenza coat when it enters the cell?

253
Q

How do viruses spread within plants?

A

Through plasmodesmata

254
Q

True or false: plant viruses recognize specific receptors to enter cells

A

False: only animal and bacterial viruses do this

255
Q

How can viral particles exit a cell?

A

Through budding or cell lysis

256
Q

What do respiratory viruses do?

A

Infect respiratory cells

257
Q

How do respiratory viruses spread?

A

Through inhalation and exhalation

258
Q

What do enteric viruses do?

A

Cause intestinal problems by damaging GI tract cells

259
Q

What is an example of an enteric virus?

A

Rotaviruses

260
Q

How do enteric viruses spread?

A

Through ingestion (fecal matter)

261
Q

How do blood-borne viruses spread?

A

Through bodily fluids (blood, semen)

262
Q

What cells does HIV affect?

A

Immune cells

263
Q

What does NCLDV stand for?

A

Nucleocytoplasmic large DNA viruses

264
Q

What are some examples of NCLDVs?

A

Herpesvirus, poxvirus, and mimivirus

265
Q

What hypothesis can be made regarding NCLDVs?

A

Primordial viruses gave rise to the first eukaryal nucleus

266
Q

What is special about Chlamydia?

A

It is a bacteria that relies on a host cell for survival

267
Q

What is Chlamydia missing for survival?

A

An ETC to synthesize ATP

268
Q

What does sequence analysis of viral genomes demonstrate?

A

Genomes of animal viruses show great similarity to host genomes, and no similarity to bacterial genomes

269
Q

What hypothesis does sequence analysis of viral genomes not support?

A

The regressive hypothesis

270
Q

How was Mavirus used in the progressive hypothesis?

A

It has a mechanism similar to transposons

271
Q

What was a major advancement in the field of virology for cultivation?

A

The development of cell culture techniques

272
Q

What are some examples of CPEs?

A

The rounding and detachment of the infected cells, or the creation of syncytiums

273
Q

What is a syncytium?

A

The fusion of individual, infected cells into a large, multinucleated mass

274
Q

What is the problem with filtration?

A

It does not concentrate the viruses

275
Q

How are the viruses concentrated?

A

Through ultracentrifugation

276
Q

What is a viral titer?

A

Concentration of a virus preparation

277
Q

What is the purpose of the latex beads in the direct count?

A

It is used to determine the exact volume, and thus concentration, of the sample

278
Q

Besides an electron microscope, what can be used to directly count the viruses?

A

Fluorescent microscopy or flow cytometry

279
Q

What is the purpose of the serial dilutions in the hemagglutination assay?

A

It can be used to determine the viral titer maximum concentration that still produces complete hemagglutination

280
Q

True or false: hemagglutination can occur without viral particles

A

True: sometimes the viral proteins alone can induce hemagglutination

281
Q

How come a plaque assay may give a different number than a direct count?

A

A direct count looks at all particles, while a plaque assay only looks at infectious particles (those that cause cell death)

282
Q

Why may viruses be defective?

A

They may have been assembled incorrectly, missing part of the genome, or contain mutations to preclude further replication

283
Q

What types of viruses are often quantified by an endpoint assay?

A

Those that cannot form plaques or cause RBCs to aggregate, but still have an observable effect on cells

284
Q

What does LD50 stand for?

A

Lethal dose 50

285
Q

What is the LD50?

A

The amount of virus to kill 50% of the infected animals

286
Q

How come an LD50 is not commonly measured?

A

It requires the use of a lot of lab animals

287
Q

What is a virus species?

A

A group whose members share several properties and occupy a common ecological niche

288
Q

What do Paramyxoviridae and Orthomyxoviridae look like under an electron microscope?

A

Enveloped, spherical, and 100-150 nm in diameter

289
Q

How are Paramyxoviridae and Orthomyxoviridae different?

A

Paramyxoviridae enter the cell by fusing with the cell membrane, and constain a linear ssRNA genome, while Orthomyxoviridae enter the cell by endocytosis, and have a segmented genome

290
Q

How was an electron microscope helpful and hurtful in the SARS outbreak?

A

They could identify the virus, but not the specific virus (thought it was paramyxoviridae, not coronavirus)

291
Q

What is an example of a viroid?

292
Q

What does PSTVd stand for?

A

Potato spindle tuber viroid

293
Q

What is missing from the viroid genome?

A

Genes that encode for proteins

294
Q

How can viroids replicate?

A

By using the cell’s RNA polymerase

295
Q

How can viroids damage the cell?

A

By diverting essential resources away from transcription, or interfering with the formation of SRP

296
Q

What does SRP stand for?

A

Signal recognition particle

297
Q

How does a viroid interact with SRP?

A

The viroid can bind to 7S RNA, interfering with the formation of SRP

298
Q

What does SRP do?

A

Directs unfolded polypeptides from the cytoplasm to the ER

299
Q

How can viroids be transmitted between plants?

A

Through insects or human activities

300
Q

How does HBV help HDV?

A

HBV provides the proteins necessary for the HDV envelope

301
Q

How are virophages similar to satellite viruses?

A

They only replicate in host cells coinfected with a helper virus

302
Q

How are virophages different to satellite viruses?

A

Virophage replication is detrimental to the helper virus

303
Q

When was the first virophage discovered?

304
Q

What is an example of a virophage?

305
Q

How does Sputnik infect a cell?

A

It replicates in amoeba infected with mamavirus, inhibiting the production of more mamavirus

306
Q

What may virophages be used for?

A

Lateral transfer of gene material

307
Q

What does CJD stand for?

A

Creutzfeldt-Jakob disease

308
Q

How do TSEs affect the brain?

A

They leave sponge-like holes

309
Q

Who first studied prions?

A

Stanley Prusiner

310
Q

How have viruses been used in research?

A

They can be used to study the inner workings of cells (DNA replication and gene regulation)

311
Q

What virus was used to study gene regulation?

A

Simian virus 40 (SV40)

312
Q

How were bacteriophages used in research?

A

They helped show that DNA, not protein, was the genetic material of cells

313
Q

What did David Baltimore and Howard Temin do?

A

Discovered reverse transcriptase

314
Q

What did Harold Varmus and J. Michael Bishop do?

A

Used virology to study cancer in the 1970s

315
Q

Which virus was used to study cancer?

A

Rous sarcoma virus

316
Q

What is a proto-oncogene?

A

Genes involved in the normal regulation of the cell cycle

317
Q

What is an oncogene?

A

Altered forms of proto-oncogenes that can lead to uncontrolled cell growth and development of tumors

318
Q

What are oncolytic viruses?

A

Viruses that infect and kill cancerous cells without harming normal cells

319
Q

How can reoviruses act as oncolytic viruses?

A

They preferentially infect cells with activated ras pathways

320
Q

What is gene therapy?

A

The process of correcting genetic defects in humans

321
Q

How can viruses be used in gene therapy?

A

They can be used to transport and deliver the gene to the host cells

322
Q

What is nanotechnology?

A

The development and use of nano-devices

BIO 315 (12 decks)

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