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(1) VMCB > Lesson 1: Introduction to the study of viruses > Flashcards

Lesson 1: Introduction to the study of viruses Flashcards

1
Q

General description of a virus

A

> obligatory intracellular infectious agents, ranging in size from 20 to 400 nanometer (nm)

> filterable agents

> cannot be seen by light microscope except poxviruses. They are seen only with the aid of an electron microscope.

> no cellular organization and do not have organelles

> contain only one type of nucleic acid, either DNA or RNA

> cannot replicate on inert media; viable host cells are required for replication

> unaffected by antibiotics

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2
Q

size of a virus

A

20 to 400 nanometer (nm)

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3
Q

example of specific picornavirus

A

Foot and Mouth-Disease virus

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4
Q

are the smallest viruses (size?)

A

picornaviruses (20nm)

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5
Q

the largest viruses (size?)

A

poxviruses (300nm)

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6
Q

These viruses cannot be seen by light microscope because of their small size except of this virus.

A

poxviruses

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7
Q

Viruses are seen only by the aid of what?

A

electron microscope

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8
Q

Viruses are composed of what?

A

nucleic acid surrounded by a protein coat

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9
Q

2 types of nucleic acid

A

DNA or RNA

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10
Q

Viruses multiply by a complex process involving what?

A

protein synthesis and nucleic acid production

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11
Q

Viruses are unaffected by these drugs

A

antibiotics

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12
Q

Three categories of viruses

A

DNA viruses
RNA viruses
Viruses that utilize both DNA
and RNA for replication

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13
Q

The viruses that infect bacteria

A

Bacteriophages or Phages

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14
Q

an infectious extracellular virus particle consists of nucleic acid (DNA or RNA) that is covered by a protein coat called capsid

A

Virion

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15
Q

Virion is an infectious extracellular virus particle consists of nucleic acid (DNA or
RNA) that is covered by a protein coat called __________.

A

capsid

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16
Q

a shell of subunits of proteins called capsomere that encloses the genome of vertebrate viruses

A

Capsid

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17
Q

capsid vs capsomere

A

capsid is the protective protein coat of viruses, whereas capsomere is the smallest subunit of viral capsid

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18
Q

subunits of proteins

A

capsomere

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19
Q

4 Functions of a Capsid

A

> offers protection for the nucleic acid against adverse
conditions

> it facilitates attachment and entry of the virus into host cell

> it possesses antigens used for virus identification in serological tests

> it determines the symmetry of the virus

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20
Q

2 types of capsid symmetry
described in viruses

A

Icosahedral and Helical Symmetries

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21
Q

the term used to refer to the combined nucleic acid and capsid which can either be naked or covered with a membrane termed an envelope

A

Nucleocapsid

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22
Q

the proteins that make up the subunit of capsid

A

Structural proteins

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23
Q

The viral genome also codes for important enzymes called__________ required for viral replication but are not incorporated in the virion.

A

non-structural proteins

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24
Q

are generally assembled in the host cell prior to incorporation of the viral nucleic acid.

A

Icosahedral capsids

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25
Q

are formed by the insertion of protein units between each turn of the nucleic acid helix, incorporating the RNA in the tubular package.

A

Helical capsids

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26
Q

a lipid bilayer and associated glycoproteins that cover a nucleocapsid

A

Envelope

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27
Q

Envelope composition

A

lipid bilayer and glycoproteins

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28
Q

are usually susceptible to detergent and are rendered non
infectious following damage to the envelope

A

Enveloped viruses

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28
Q

the proteins encoded by viral nucleic acid for binding to receptors on host cells, membrane fusion, uncoating of the virion and destruction
of receptors on host cells

A

Glycoproteins

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29
Q

knob-like projections from the envelope formed from the oligomers of glycoproteins.

A

Peplomers or Spikes

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30
Q

Peplomers or spikes are formed from what?

A

oligomers of glycoproteins

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31
Q

Present in certain viruses including coronaviruses, retroviruses, orthomyxoviruses, rhabdoviruses and
paramyxoviruses

A

Peplomers or spikes

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32
Q

Peplomers or spikes are present in certain viruses including such as the ff:

A

> coronaviruses
retroviruses
rhabdoviruses
orthomyxoviruses
paramyxoviruses

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33
Q

used to bind to cell receptors or may have enzymatic activity

A

Peplomers or spikes

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34
Q

a layer of protein present between the nucleocapsid and the
envelope in some enveloped viruses that provides additional rigidity to the virion

A

Matrix protein

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35
Q

Components of an enveloped virus

A

> Membrane
Lipids
Proteins
Glycoprotein

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36
Q

Properties of an enveloped virus

A

> Environmentally labile; disrupted by acid, detergents, drying, and heat

> Modifies cell membrane
during replication

> Released by budding and cell lysis

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37
Q

enveloped viruses are released through?

A

budding and cell lysis

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38
Q

Biological functions of an enveloped virus

A

> Must stay wet

> Cannot survive in the
gastrointestinal tract

> Spreads in large droplets, secretions, organ transplants, and blood transfusion

> Does not need to kill the cell to spread

> May need antibody and cell-mediated immune response for protection and control

> Elicits hypersensitivity and inflammation to cause immunopathogenesis

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39
Q

Component of a non-enveloped/naked virus

A

Protein

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40
Q

non-enveloped/naked viruses are released from cell by?

A

lysis

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40
Q

Properties of a non-enveloped/naked virus

A

> Environmentally stable to temperature, acid, proteases, detergents, and drying

> Is released from cell by lysis

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41
Q

Biological functions of a non-enveloped/naked virus

A

> Can be spread easily through fomites, from hand to hand, by dust, and by small droplets

> Can dry out and retain infectivity

> Can survive the adverse
conditions of the gut

> Can be resistant to detergents and poor sewage treatment

> Antibody may be sufficient for immunoprotection

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42
Q

viruses are named according to what? give examples

A

> type of disease they cause
Examples
include poxviruses, herpesviruses (creeping lesions)

> based on acronyms of disease
** (papovavirus-papilloma; polyoma–vacuolating)** or acronym of observable characteristics (picornavirus - pico/small–rna–virus)

> based on morphology Coronaviruses (halo or corona/crown of spikes), Togavirus (Toga/cloak), Rhabdovirus (Rhabdo/Rod-shaped), Calicivirus (Calix/cup-shaped depression)

> after geographical regions where they were first isolated ** (E. g. Coxsackie-, Marburg-, Gumboro-, Mokola- virus)**

> after individual discoverer (Epstein-Barr virus)

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43
Q

Someviruses are named according to the type of disease they cause. Give examples.

A

poxviruses, herpesviruses (creeping lesions)

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44
Q

Other are named based on acronyms of disease or acronym of observable characteristics . Give examples.

A

papovavirus-papilloma
polyoma–vacuolating)

(picornavirus
pico/small–rna–virus)

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45
Q

herpesviruses also known as what?

A

creeping lesions

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46
Q

papovavirus meaning?

A

papilloma

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47
Q

polyoma meaning?

A

vacuolating

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48
Q

picornavirus meaning?

A

pico/small–rna–virus)

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49
Q

Viruse are also named based on morphology as revealed by electron microscopy. Give examples.

A

> Coronaviruses (halo or corona/crown of spikes)

> Togavirus (Toga/cloak), Rhabdovirus

> (Rhabdo/Rod-shaped),

> Calicivirus (Calix/cup-shaped depression)

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50
Q

Coronaviruses meaning?

A

halo or corona/crown of spikes

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51
Q

Togavirus meaning?

A

Toga/cloak

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52
Q

Rhabdovirus meaning?

A

Rhabdo/Rod-shaped

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53
Q

Calicivirus

A

Calix/cup-shaped depression

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54
Q

Some viruses are named after geographical regions where they were first isolated. Give examples

A

Coxsackie-virus
Marburg-virus
Gumboro-virus
Mokola-virus

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55
Q

Occasionally, viruses are named after individual discoverer. Give example.

A

Epstein-Barr virus

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56
Q

five hierarchical levels

A

order
family
subfamily
genus
species

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57
Q

established in 1973, developed and expanded the universal scheme in which characteristics of
virions are used to assign them to five hierarchical levels (order, family, subfamily, genus and species)

A

International Committee on Taxonomy of Viruses (ICTV)

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58
Q

The hierarchical levels are denoted with the following suffixes:

A

 Order: -virale
 Family: -viridae
 Genus: -virus
 Species:- virus

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59
Q

Order suffix

A

-virale

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60
Q
A
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60
Q
A
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61
Q
A
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62
Q
A
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63
Q

Four orders containing viruses of animals

A

Mononegavirale
Herpesvirales
Picornavirales
Nidovirales

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63
Q

Genus suffix

A

-virus

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63
Q

Family suffix

A

-viridae

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64
Q

Species suffix

A

-virus

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65
Q

Order Mononegavirale families

A

(PaRaBeFore)
Paramyxoviridae, Rhabdoviridae, Bornaviridae and Filoviridae

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66
Q

Members of this order have common attributes
including a single stranded, non-segmented, negative sense RNA genome, similar replication strategies

A

Mononegavirale

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67
Q

Order Herpesvirales families

A

(HAM)
Herpesviridae, Alloherpesviridae and Malacoherpesviridae

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68
Q

Order Picornavirales families

A

(PIDMS)
Picornaviridae, Iflaviridae,
Dicistroviridae, Marnaviridae and Secoviridae

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69
Q

Order Nidovirales families

A

(CAR)
Coronaviridae, Arteriviridae and
Roniviridae

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70
Q

are infectious particles, which can transmit a disease, composed mainly of a protein without any detectable nucleic acid

A

Prions

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71
Q

apparently have no virion structure or genomes and evoke no immune response in the infected host.

A

Prions

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72
Q

These are extremely resistant to inactivation by heat, disinfectants, and radiation

A

Prions

73
Q

causative agents of slow viral infections, such as subacute spongiform encephalopathy

A

prions

74
Q

slow viral infections

A

subacute spongiform encephalopathy

75
Q

After long incubation period of years, they produce a progressive disease that causes damage to the central nervous system, leading to subacute spongiform encephalopathy.

A

Prions

76
Q

True or False
Viruses are more resistant than bacteria to chemical disinfectants such as phenol.

A

True

77
Q

Active virucidal agents

A

formaldehyde and betapropiolactone

78
Q

most active antiviral disinfectants

A

> hydrogen peroxide
potassium permanganate
hypochlorite
organic iodine compounds

79
Q

Most of the viruses with few exceptions are highly heat labile. They are inactivated within seconds at _____, within minutes at _____, and within days at _____.

A

56°C
37°C
4°C

80
Q

The viruses usually remain viable in a pH range of ______, but are sensitive to extremes of acidity and alkalinity

A

5–9

81
Q

active against enveloped
viruses but are not active against non-enveloped/naked viruses

A

Ether, chloroform, and detergents

82
Q

the viruses are readily inactivated by these radiations

A

sunlight, ultraviolet (UV) radiations, and ionizing radiations

83
Q

Viruses rely completely on what for their replication.

A

living host cells

84
Q

it carries the genetic information of the virus

A

viral nucleic acid

85
Q

The replicative cycle of a virus may range from how many hours?

A

6-40 hours

86
Q

Within hours of infection, this phase occurs.

A

eclipse phase

87
Q

It is the initial stage of virus replication whereby the infecting virus loses its physical identity and most or all of its infectivity. At this time, no virus is detectable in the infected host by methods such as virus
assay or electron microscopy.

A

eclipse

88
Q

new viral particles are formed and released from the cell wherein the number of viral particles increases exponentially

A

productive stage

89
Q

The Virus Replication Cycle

A
  1. Inoculation: inoculum of virus binds to cell
  2. Eclipse: virions penetrate the cells
  3. Burst: host cells release many viral particles
  4. Burst size: number of virions released per bacterium
90
Q

Steps in virus replication

A

1. Attachment
2. Entry
Mechanism of entry:
A. Endocytosis
B. Fusion
C. Direct introduction of viral genome into the cytoplasm (injection) through
channels in the plasma membrane.
3. Uncoating
4. Biosynthesis or Replication of nucleic acid
5. Maturation/Assembly of virus
6. Release of the daughter virion

91
Q

Virus receptors on cells

A

glycoproteins or glycolipids, proteoglycans

92
Q

following attachment, the virus gains access to the host cell internal environment where replication takes place

A

Entry

93
Q

an active process by which nutrients and other molecules are brought into a cell

A

Endocytosis

94
Q
A
95
Q
A
96
Q
A
97
Q
A
98
Q

Example of Endocytosis which is used by cells to internalize receptor-bound ligands, fluid, lipids and membrane proteins

A

clathrin-mediated endocytic pathway

98
Q

receptor-based endocytosis also known as?

A

viropexis

99
Q

enveloped viruses enter the cell by an alternate method called ________ in which the viral envelope fuses with the plasma
membrane and releases the capsid into the cell cytoplasm

A

Fusion

99
Q

Fusion can be seen in these viruses

A

retroviruses, paramyxoviruses, and herpesviruses

100
Q

Direct introduction of viral genome into the cytoplasm (injection) through channels in the plasma membrane. This is seen in some non envelope viruses such as

A

picornaviruses

101
Q

It is the process of separation of viral nucleic acid from its protein core for transcription to take place.

A

Uncoating

102
Q

However, in certain viruses, transcription may proceed without complete release of the viral genome. Example?

A

reoviruses

103
Q

Uncoating may occur here

A

cell membrane, cytoplasm, or nucleus

104
Q

Uncoating may lead to what?

A

loss of virus infectivity

105
Q

Some viruses (most DNA viruses) makes use of the host cells enzymes called _______ to synthesize mRNA,

A

transcriptases

106
Q

Most RNA viruses generate its own enzyme called _______ to transcribe and replicate mRNA

A

polymerase

107
Q

DNA viruses replicate their DNA in the _______ of the host cell by using _______ enzymes

A

nucleus
viral enzymes

108
Q

DNA viruses synthesize their capsid and other proteins in the _______ by using ______ enzymes.

A

cytoplasm
host cell

109
Q

the complete, infective form of a virus outside a host cell

A

virions

110
Q

DNA viruses

A

(HAPH)
herpesvirus, adenovirus, and papovavirus, hepadnavirus

111
Q

Poxvirus is an exception, because all of its components are synthesized in the _______.

A

cytoplasm

111
Q

Most of the DNA viruses synthesize their nucleic acid in the host cell _______.

A

nucleus

112
Q

The RNA viruses replicate in the ________

A

cytoplasm

113
Q

The RNA viruses replicate in the cytoplasm except these viruses

A

Orthomyxoviruses and Borna disease virus

114
Q

have a non-obligatory
nuclear phase of replication

A

paramyxoviruses

115
Q

these viruses which replicate via a DNA
intermediate (provirus)

A

retroviruses

116
Q

During the Replication of RNA viruses, transcription occurs in the ________ under the direction of a viral transcriptase.

A

cytoplasm

117
Q

RNA viruses

A

paramyxoviruses, retroviruses, orthomyxoviruses, Borna disease virus

118
Q

It is the first step in viral maturation.

A

assembly of the protein capsid

119
Q

are present in the host cell as fully developed virion

A

Non-envelope viruses

119
Q

acquire their envelope from plasma membrane during their release

A

envelope viruses

120
Q

The envelope develops around the capsid by a process called ________.

A

budding

121
Q

The assembly of
various viral components into virions may take place in the nucleus. Give examples

A

herpesvirus and adenoviruses

122
Q

The assembly of various viral components into virions may take place in the cytoplasm. Give examples

A

picornaviruses and
poxviruses

123
Q

It is surrounded by an envelope, which is derived from the host cell membrane during the process of budding.

A

nucleocapsid

124
Q

enveloped viruses are released through what process?

A

exocytosis

125
Q

Abnormal replicative cycles may occur in four ways

A
  1. Incomplete viruses
  2. Pseudovirions
  3. Abortive infections
  4. Defective viruses
126
Q

Due to defect during assembly of viral components, some of the daughter virions that are produced may not be infective.

A

Incomplete viruses

127
Q

are the viruses that occasionally enclose host cell nucleic acid instead of viral nucleic acid, therefore, are non infective and lack the capability to replicate

A

Pseudovirions

128
Q

In this type of infection, the virus components may be synthesized but the maturation is defective maybe due to infection of the wrong host cells by the virus.

A

Abortive infections

129
Q

These are viruses that produce fully mature virions only in the presence of helper viruses which supplement the genetic deficiency in the defective viruses.

A

Defective viruses

130
Q

Example of a Defective virus

A

Hepatitis D virus

131
Q

It replicate only in the presence of hepatitis B virus (helper viruses).

A

Hepatitis D virus (defective virus)

132
Q

The viruses show variation in their genomic structure by two principal methods

A

mutations and recombination

133
Q

Spontaneous and random errors in the copying of viral nucleic acid

A

Mutations

134
Q

Mutation may be induced by what?

A

mutagens

135
Q

Mutation may be induced by mutagens like?

A

X-rays, UV irradiation or chemical agents, or may occur spontaneously

136
Q

resulting from single nucleotide substitutions, are the most common type of mutation

A

Point mutations

137
Q

Less common types of mutation

A

deletion or insertion of
one or more nucleotides

138
Q

a new area of antiviral research wherein those RNA viruses with inherently high mutation rates are administered with mutagenic agents to drive viral extinction through violation of the error threshold and error catastrophe

A

Lethal mutagenesis

139
Q

is the extinction of an organism as a result of excessive mutations

A

Error catastrophe

140
Q

a virus mutant which can replicate only under defined permissive conditions

A

Conditional-lethal mutants

141
Q

rendering a virus towards low viral load and low viral fitness by subjecting it to a combination of mutagenic agents and antiviral compounds

A

Viral suppression

142
Q

variant strains showing differences in the tissue type and species of target cells affected by viruses

A

Host-range mutants

143
Q

viruses that replicate in the presence of antibody. Because of altered antigenic surface determinants, the mutants are unaffected by neutralizing antibodies induced by the wild-type virus. Such a selection process may facilitate persistent or recurring infections

A

Antibody escape mutants

144
Q

a virus with decreased infectious titer despite a high number of viral particles. This mutant promote the establishment and maintain persistent infections

A

Defective-interfering mutants

145
Q

variant strains that cause less serious infections in human and animals.

A

Attenuated mutants

146
Q

the exchange or transfer of genetic material between different but closely related viruses infecting the same cell simultaneously, or between virus and host cell

A

Recombination

147
Q

occurs between two closely related DNA or RNA viruses

A

Intramolecular recombination

148
Q

a recombination between positive-sense single stranded RNA viruses and occurs through a template switching mechanism; RNA polymerase switches between template strands during synthesis of the complementary negative-sense strand

A

Copy-choice (template switching)

149
Q

Copy-choice (template switching) can occur in these viruses

A

picornaviruses, togaviruses and coronaviruses

150
Q

An exchange of segments occurs between these viruses, resulting in production of new hybrid strains

A

Reassortment

151
Q

infectious progeny are produced from parental viruses, of which one or both are non-infectious, following mixed infection of a cell

A

Reactivation

152
Q

when infectious progeny are produced from related viruses inactivated by lethal mutations at different loci in their genomes

A

Multiplicity reactivation

153
Q

It occurs when an inactivated virus becomes capable of replicating after acquiring genetic material from an infective virus

A

Cross-reactivation or genome rescue

154
Q

widely used for virus propagation

A

Tissue culture

155
Q

It is employed for the isolation and production of particular viruses

A

inoculation of chick
embryos and experimental animals

156
Q

It is required for the isolation and identification of viruses involved in disease, for the titration of viruses for vaccine production and for the provision of stocks for research purposes

A

Propagation

157
Q

2 types of tissue culture

A

A. Explant cultures
B. Cell cultures

158
Q

Three types of cell
culture

A

a) Primary cell culture
b) Semi-continuous
c) Continuous cell cell culture

159
Q

a tissue fragment is used to isolate viruses from animals with persistent infection

A

Explant cultures

160
Q

the tissues are digested into individual cells by mechanical cutting followed by digestion with enzymes such as trypsin

A

Cell cultures

161
Q

type of cell culture derived directly from tissues and contain many cell types such as epithelial cells, fibroblasts, keratinocytes, melanocytes, endothelial cells, muscle cells, hematopoietic cells, mesenchymal stem cells, etc.

A

Primary cell culture

162
Q

type of cell culture where cells of semi-continuous or diploid cell lines retain their characteristic diploid chromosomal constitution and can support the growth of a wide range of viruses. However, such cell lines, tend to die out between the 30th and 50th passage

A

Semi-continuous

163
Q

type of cell culture which are derived from either normal or neoplastic tissue and can be passaged indefinitely

A

Continuous cell cell culture or immortal cell lines

164
Q

How to detect viral growth in cell cultures

A

> light microscopy
Serological tests using fluorescein-labeled antibody

165
Q

Two types of virus according to cytopathic effect (CPE) production

A

a) Burster (lytic) virus
b) Creeper virus

166
Q

these induce formation of multinucleated giant cells

A

Creeper virus

166
Q

induce cell lysis and cellular transformation in cell culture

A

Burster (lytic) virus

167
Q

Serological tests

A

> Inoculation on embryos
Use of experimental animals

168
Q

though no longer extensively used, this remains the preferred method for isolation of influenza A viruses and for many avian viruses

A

Inoculation on embryos

169
Q

Inoculation on embryos modes of inoculation

A

via the:
> allantoic cavity
> amniotic cavity or the
yolk sac
> chorioallantoic membrane (CAM), or intravascularly

170
Q

Inoculum of virus binds to cellls

A

Inoculation

171
Q

Virions penetrate the cells

A

Eclipse

172
Q

Host cells release many viral particles

A

Burst

173
Q

Number of virions released per bacterium

A

Burst size

174
Q

Mechanism of entry of a Virus

A

A. Endocytosis
B. Fusion
C. Direct introduction of viral genome into the cytoplasm (injection) through
channels in the plasma membrane

175
Q

This is seen in some non-envelope viruses such as picornaviruses

A

Direct introduction of viral genome into the cytoplasm (injection) through channels in the plasma membrane.

176
Q

Define the 3 Mechanism of Entry

A

a. Endocytosis - an active process by which nutrients and other molecules are
brought into a cell
b. Fusion - enveloped viruses enter the cell by an alternate method
c. Direct introduction of viral genome into the cytoplasm (injection) through channels in the plasma membrane. - This is seen in some non-envelope viruses such as picornaviruses

177
Q

It is where naked viruses or non-enveloped viruses undergo a
receptor-based endocytosis

A

Endocytosis

178
Q

in these viruses, transcription may proceed without the complete release of the viral genome

A

reoviruses

179
Q

In some viruses it is facilitated by lysosomal enzymes present inside the phagocytic vacuoles and
Golgi vesicles of the host cell that degrade the protein of the viral capsid

A

Uncoating

180
Q

it leads to loss of virus infectivity

A

Uncoating

181
Q

Difference between negative-sense strand and positive-sense strand

A

The negative-sense strand of each segment is transcribed to produce individual mRNA molecules. In contrast, the genomes of positive-sense, single-stranded RNA viruses can act directly as mRNA following infection.

(1) VMCB (13 decks)

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