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Viruses Flashcards

0
Q

Do viruses grow or divide?

A

No

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1
Q

How small of viruses?

A

nm in size

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2
Q

What are viruses?

A

Agents that can pass through filters that trap most known bacteria

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3
Q

What are viruses able to infect?

A

Most living organism, animals, plant, fungi, bacteria

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4
Q

What are common features viruses share?

A

Have a protein coat, capsid- encapsulating the genetic material

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5
Q

What is a virion?

A

A whole virus particle

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6
Q

What percentage of protein are viruses composed of?

A

50-90%

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7
Q

What are the three main functions of proteins in viruses?

A

Protects the genome (form nuclease enzymes, UV)
Allows recognition of and release form host cells
Enzymes necessary for infection (nucleic acid replication)

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8
Q

Why are capsid symmetrical in appearance?

A

Due to precise assembly of repeated protein sununits

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9
Q

Why are capsid symmetrical in appearance?

A

Due to precise assembly of repeated protein subunits

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10
Q

What are virus particles held together by?

A

Hydrophobic and electrostatic interactions (not covalent bonds)

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11
Q

What are the 2 main classes of virus capsid structure?

A

Helical and icosahedral symmetry

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12
Q

What are the properties of virus particles?

A 
Protection
Recognition
Self- assembly
Fidelity
Economy
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13
Q

What are virus capsids composed of?

A

Proteins. Proteins fold into nonsymmertical (tertiary) structures

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14
Q

What are the two ways asymmertcial subunits can form particles?

A

Helical and cubical

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15
Q

What is Frankel-Conrat and Williams demonstrate?

A

That when purified proteins and RNA of tobacco mosaic virus are mixed, virus particles spontaneously form- the particle is the minimum free energy state

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16
Q

What symmetry does a tobacco mosaic virus have?

A

Helical symmetry producing a rod shaped capsid

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17
Q

What symmetry does Poliovirus have?

A

Icosahedral capsid (of 3 different proteins)

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18
Q

What do both type of capsid have?

A

A surrounding lipid envelope, derived form the host cell membrane

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19
Q

What does virus particle contain?

A

Capsid

nucleiocapsid

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20
Q

What are the two types of viruses?

A

Enveloped and naked (non-enveloped)

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21
Q

What is the capsid called in a enveloped virus?

A

nucleocapsid

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22
Q

What is the nucleocapsid surrounded by?

A

A lipid (bilayer) membrane that is usually embedded with glycoprotein (involved in cell infection) forming the envelope.

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23
Q

What can envelope make viruses appear?

A

non-symmetrical shapes
Or
pleomorphic (change shape)

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24
Q

What are between the nucleocapsid and envelope?

A

tegument or matrix proteins which often link the nucliocapsid and envelope

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25
Q

What can viruses genomes be?

A

DNA or RNA, and either double or single-stranded

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26
Q

What is a nucleocapsid?

A

the capsid of a virus with the enclosed nucleic acid.

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27
Q

What are the two types of viral shapes?

A

Icosahedral and helical

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28
Q

What does virus classification take in to account?

A

Genome type
Capsid structure
Disease pathology ect.

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29
Q

What is the classification system of viruses?

A

Species
Genus
subfamily
Family

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30
Q

What are the major virus groups based on genetic material?

A

dsDNA, ssDNA, dsRNA, ssRNA

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31
Q

What can the RNA genomes produce?

A

Proteins with no DNA involved

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32
Q

What can ssRNA be divided into?

A

Positive or negative sense

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33
Q

What are proteins produced directly form?

A

Positive sense RNA

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34
Q

What does negative sense RNA need to be copied into before a protein can be produced?

A

Negative sense RNA needs to be copied into positive sense first

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35
Q

Which two types of genetic material viruses uses reverse transcriptase enzyme in their replication?

A

ssRNA and dsDNA

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36
Q

What are the seven classes of virus according to the Baltimore Classification ?

A 
dsDNA
ssDNA
dsRNA
\+ssRNA
-ssRNA
RNA reverse transcribing viruses
DNA reverse transcribing viruses
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37
Q

What is the pathology of viral disease caused by?

A

Toxicity of virus gene products on cell metabolism.
Reactions of host to infected cells.
Modification of cell function by virus gene products

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38
Q

What must a virus do in order to multiply?

A

infect a susceptible cell at the portal of entry

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39
Q

What are the steps when a virus enters a cell?

A

Transferring genetic material- essential proteins.

Viral genes lead to production of viral proteins

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40
Q

What does production of viral proteins in host cell ensure?

A

Replication of genome
Packaging genome into virions
Effect structure and/or function of infected cell

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41
Q

What do viruses rely on during replication?

A

Depending on number of viral genes they depend on host proteins during replication

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42
Q

What is progeny?

A

An organism produced as a result of replication. New progeny viruses are released form cell

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43
Q

What is a bacteriophage?

A

a virus which parasitizes a bacterium by infecting it and reproducing inside it.

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44
Q

What is the eclipse phase?

A

The period of time between infection by a virus and the appearance of the mature virus within the cell.

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45
Q

What happens following infection?

A

And for few hours (eclipse phase), only parental virus is detectable. Virus genome exposed, gene expressed, interact with cell proteins.

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46
Q

What happens in the maturation and release phase?

A

Progeny virus builds up in the cell exponentially and either causes the cell to burst (lysis) or bud out through the cell membrane

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47
Q

How much do virus release and cycle?

A

Release 1-100k and cycle 8-72h

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48
Q

What are the three types of infection by a virus?

A

Productive
Restrictive
Abortive

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49
Q

What does permissive cells mean?

A

that the virus is able to circumvent host defences and is able to replicate

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50
Q

What does the productive infection involve?

A

Permissive cells

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51
Q

what does the restrictive infection involve?

A

Partly permissive cell or cell population

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52
Q

What does abortive cells involve?

A

Non- permissive cell (not all virus genes expressed) virus lacks some genes

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53
Q

What some viruses have in regards to productive infection?

A

Short (acute)
Long (persistent)
They go into the lytic cycle

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54
Q

What can viruses enter if the stimulus to enter the lytic cycle is absent?

A

A non-lytic cycle or lysogency

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55
Q

What was the first example a lytic infection carried out by?

A

A bacteriophage of e.coli called lambda

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56
Q

What is lysogenic infection?

A

A typical of non-bacterial viruses

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57
Q

What is a latent infection?

A

Virus latency (or viral latency) is the ability of a pathogenic virus to lie dormant (latent) within a cell, denoted as the lysogenic part of the viral life cycle

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58
Q

Give example of viruses in which latent infection occurs?

A

herpesviruses,HIV-1 and some parvoviruses

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59
Q

How can virus genome be maintained in a host?

A

Interfaced in host DNA or as free episome

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60
Q

What does attachment involve?

A

A virion protein binds to a specific cell surface receptor. Can be in form of a spike projecting form the capsid or embedded in the viral envelope.

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61
Q

What is the penetration step?

A

A fast, energy-dependent step

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62
Q

How do non-enveloped viruses enter during the penetration step?

A

Directly across the membrane via endocytosis into cytoplasmic vacuoles

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63
Q

How do enveloped viruses enter during the penetration step?

A

The envelope and the cell membrane fuse (via protein: receptor interaction) allowing the nucleocapsid to enter the cell

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64
Q

What is uncoating?

A

Where the vision fully or partially disintegrates (sometimes aided by cell enzymes; acid pH in endoscopes often critical) exposing viral genome

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65
Q

What is the central dogma in a protein?

A

Replication, transcription and translation

DNA-RNA-Proteins

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66
Q

What two events are critical to viral infection?

A

The production of virus structural proteins and enzymes

The replication of the viral genome (dsDNA, ssDNA, dsRNA, ssRNA)

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67
Q

What happens after uncoating?

A

Gene expression, genome replication and progeny assembly

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68
Q

What does DNA need to transcribed into?

A

mRNA, that is then translated into proteins

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69
Q

Where do most events take place for a herpesvirus?

A

The nucleus

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70
Q

Where do most events take place for a poxviruses?

A

The cytoplasm

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71
Q

What shape genome is RNA viruses?

A

linear

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72
Q

What is viral genome integrated as in the hosts chromosome?

A

cDNA

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73
Q

What do non enveloped viruses undergo?

A

Assembly of capsid with genome inside and maturation where protein cleavage to stabilise and make infective within host cell, and usually lyse cells during release (egress)

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74
Q

What does maturation involve in enveloped viruses?

A

Inserting viral glycoproteins in a cell membrane. This is usually the outer membrane

75
Q

What do the glycoproteins interact with in enveloped viruses?

A

With nucleocapsid pulling the membrane around it. The mature virio the. Buds out of the cell during egress

76
Q

What does the insertion of glycoproteins I the outer membrane make?

A

The infected cell a target for the host immune system

77
Q

What do the number of genes in a viruses vary from?

A

10100

78
Q

What are viruses have though to have originated from?

A

Either degenerate cells or from break away cell genetic material able to replicate

79
Q

Can virus DNA be mutated?

A

Yes

80
Q

Why is RNA particularly mutable?

A

As its not proofread during synthesis unlike DNA

81
Q

What is antigenic drift?

A

Antigenic drift is a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites.

82
Q

What can genome segment reassortment lead to?

A

New strains via antigenic shift

83
Q

What is the family of the influenza virus?

A

Orthomyxoviridae

84
Q

What type of virus is influenza virus?

A

Enveloped, pleomorphic; -negative sense ssRNA

In 8 segments (1-2kbp)

85
Q

What does influenza virus affect?

A

Specific mammals

But type A host birds are natural reservoir in wild aquatic birds

86
Q

What is the portal entry of influenza virus and target cells?

A

Epithelial mucosa via aerosol

Targets lower respiratory tract

87
Q

What are the symptoms and pathology of influenza?

A

Cough,fever, acute infection

Pathology is epithelial cells, pneumonia

88
Q

What are envelope spike do?

A

Spikes of haemagglutinin binds to sialic acid sugars on cell surface and neuraminidase enzyme cleaves sialic acid in egress. H and N act as antigens for immune antibody response

89
Q

What is the most important antigen?

A

Haemagglutinin- protective antibodies raised against HA

90
Q

What does drift require in regards to vaccines?

A

For vaccines to be produced every season based on the latest circulating strain in the other hemisphere of the globe

91
Q

What can shift result in?

A

A pandemic e.g. Swine flu

92
Q

What are killed vaccines?

A

Where isolates are inactivated or detergent treated to release H and N proteins

93
Q

What are antiviral drugs used to treat?

A

Early infections e.g. Neuraminidase analogues osteltamivir which competitively inhibits NA cleaving HA from sialic acid, reducing viral egress

94
Q

What is the family of herpes simplex virus?

A

herpersviridae

95
Q

What type of virus is herpes simplex virus?

A

Enveloped, icosahedral, linear dsSNA, 70 genes, circularises in cell

96
Q

What is the target host for herpes simplest and what is the portal of entry?

A

Skin or epithelial mucosa via saliva. It targets cells is neurons: axon- dorsal root ganglia

97
Q

What are symptoms and pathology of herpes simplex?

A

Nerve tingling on reactivation the pathology is epithelial blisters (cold sores) sometimes eye infections or encephalitis. Acute infection-latency

98
Q

What causes reactivation of herpes simplex virus from latency?

A

immunocompromised and this produces local blisters

99
Q

When do enveloped spikes of herpes simplex bind to?

A

Envelope spikes of Glycoprotein (gC) bind to heparin sulphate proteoglycan on cell

100
Q

What controls the extent of the infection caused herpes simplex?

A

humoral (antibody) and cell-mediated immune response control the extent of infection

101
Q

What are herpetic diseases caused by HSV-1?

A

Cold sores of the mouth
Lesions on the lip
Herpes keratitis of the eye
Herpes infection- from contact sports

102
Q

What are 90% of herpes diseases caused by?

A

HSV-2

103
Q

What percentage of cases does HSV-1 cause gential herpes?

A

10%

104
Q

What is the treatment of herpes simplex virus (HSV)?

A

No vaccine but nucleoside analogues antiviral drugs such as ACV are used

105
Q

What activates ACV?

A

HSV thymidine kinase gene(TK)

106
Q

What is TK involved in?

A

Nucleoside synthesis for DNA

107
Q

Why can’t HSVTK uses ACV as a substrate?

A

HSVTK has evolved substantially differently than human TK

108
Q

What does HSVTK convert ACV to?

A

ACV-monophosphate. Cell kinase enzymes add another 2 phosphates

109
Q

How is ACV-triphosphate incorporated into viral DNA?

A

Preventing replication- acutely infected cells die, but not latent infections as HSVTK gene not expressed during latency

110
Q

What is chickenpox caused by?

A

varicella zoster virus

111
Q

What does Epstein-Barr virus cause?

A

80% cases of infectious mononucleosis/glandular fever. leads to cancer in some individuals

112
Q

What does cytomegalovirus cause?

A

Produces 20% infectious mononucleosis then dormancy. Reactivation in immunocompromised

113
Q

How is herpesvirus destroyers in the environment?

A

Its fragile and easily disrupted by heat, dedication. 70% alcohol, soap and detergent

114
Q

Why is herpesvirus sensitive to the environment?

A

the envelope is extremely sensitive to damage; the virus is usually transmitted by direct contact with mucosal surfaces or secretions of an infected person. The virus can dry out and become damaged when exposed to air- cannot be transmitted by toilet seats

115
Q

What is Kaposi sarcoma-associated virus detected in?

A

All Kaposis sarcomas, an aggressive pigmented sarcoma of the skin.

116
Q

What is Kaposi virus transmitted by?

A

Saliva, its easily diagnosed by biopsy. It is an earliest manifestation of AIDS

117
Q

What is the family of papillomavirus?

A

papilomaviridae

118
Q

What type of virus is the papillomavirus?

A

Non- enveloped, icosahedral, circular, dsDNA 8kb, 9 genes

119
Q

What is the host for papillomavirus?

A

Specific types infect birds, mammals

120
Q

What is the portal of entry for the papillomavirus?

A

Small wounds in skin or mucosa via direct contact

121
Q

What is the pathology of papillomavirus?

A

Benign tumours, cervical cancer. Some infect oncogenic. Acute infection to latency where reactivation is caused by immunocompromised.

122
Q

What do the envelope spikes on the virus bind to?

A

Heparin sulphate proteoglycan on cell

123
Q

What 2 papillomavirus gene products inacrivate the cells tumour suppressor proteins p53 and Rb?

A

E6 and E7 respectively. Causing cell growth- benign/ premalignant tumours.

124
Q

What do Gardasil and Cervarix vaccines consist of?

A

purifies L1 capsid protein

125
Q

What is the family name of the Poliovirus?

A

picornoviridae

126
Q

What type of virus is Poliovirus?

A

A non-enveloped, icosahedral, + sense ssRNA, 7.5kb encodes a single polyprotein that is cleaved into 10 polypeptides

127
Q

What is the host of the Poliovirus and the portal of entry?

A

Human. Oral via rascally contaminated water or food. Infects epithelium of pharynx and gut. It targets epithelium and blood cells

128
Q

What are the symptoms and pathology of Poliovirus?

A

Fever, intestine problems, headache, paralysis, death.
Pathology is poliomyelitis- inflammation of grey matter of spinal cord/CNS motor neurons mostly in immune deficient or infants

129
Q

What does vision protein 1 interact with?

A

Poliovirus receptor (PVR) an immunoglobulin glycoprotein on cell surface

130
Q

Where does replication of the Poliovirus occur?

A

In cytoplasm via viral RNA-dependent RNA polymerase.

131
Q

What does asymptomatic mean?

A

Producing no symptoms

132
Q

What % of Poliovirus infections are asymptomatic?

A

95%

133
Q

What asymptomatic people able to do?

A

shed virus in stool and are able to transmit the virus to others

134
Q

What % of Poliovirus infections produce mild symptoms?

A

4-8%

135
Q

What are mild symptoms of Poliovirus infection?

A 
Malaise
Gastrointestinal distress
Fever
Influenza-like illness
sore throat 
Recovery within a week
136
Q

What % of Poliovirus infections cause major illness?

A

Less than 1%

137
Q

What are major symptoms of Poliovirus?

A

Flaccid paralysis- weakness
Inflammation and sometimes destruction of neurons
Recovery can take up to two years and may be incomplete

138
Q

What is the vaccine of Poliovirus?

A

Formalin-inactivated dead vaccine of the three Poliovirus serotypes

139
Q

What is the oral live vaccine of Poliovirus?

A

non-virulent, attenuated strain

140
Q

How is Poliovirus attenuated?

A

By serial passage in cell culture- enriches weaker mutated viruses

141
Q

What does the vaccines stimulate?

A

Neutralising antibody production

142
Q

What can some attenuated viruses revert to?

A

Virulence when passes through the gut (1 in a million cases)

143
Q

What is the family of the Human immunodeficiency virus 1?

A

retroviridae

144
Q

What type of virus is HIV 1?

A

Enveloped, helical, 2 genome copies of positive sense ssRNA, 10kb, 9 genes

145
Q

What is the host, portal of entry and target cells of HIV 1?

A

Humans. Mucosa via fluids, blood

Targets CD4+ T cells, macrophages

146
Q

What are symptoms and pathology of HIV 1?

A

Fever, malaise, lymph node swelling.
Pathology: depletion of CD4+ cell count leads to acquired immunodeficiency syndrome (AIDS) and opportunistic infections and death

147
Q

What do enveloped gp120 glycoprotein bind to?

A

CD4 molecules or chemokine receptors on cell. Though that dendritic cells at portal site are infected then pass virus onto T cells/macrophages

148
Q

What does the reverse transcriptase convert?

A

ssRNA to dsDNA which is integrated into cell genome vain viral integrase

149
Q

What happens after initial cute infection of HIV 1?

A

Get latency for weeks to years

150
Q

What are treatments for HIV 1?

A

No HIV vaccine. Anti-retroviral therapy is via a mix of drugs; RT inhibitors and often a protease inhibitor where no genomic dsDNA is made. Processing of proteins for virion assembly is prevented.

151
Q

What is the oncogene virus?

A

Rous Sarcoma

Led to discovery of Arc gene- a protein kinase gene

152
Q

What can retrovirus alter?

A

TS or proto-oncogene expression by integration of their genome into cell DNA

153
Q

What are bacteriophage?

A

Viruses that infect bacteria

154
Q

What family is bacteriophage from?

A

Siphoviridae

155
Q

What is the genome of bacteriophage?

A

dsDNA genome and some RNA

156
Q

What is the virion structure of a bacteriophage?

A

Tail fibres bind to cell surface receptors , then pins, then DNA injected into host

157
Q

What life cycles do bacteriophage have?

A

Lytic, lysogenic

158
Q

What happens in lysogeny of a bacteriophage?

A

prophages integrate in host genome or exist episomally, receiving into lytic cycle under certain conditions.

159
Q

What happens in lytic cycle of bacteriophage?

A

Viral proteins may modify cell RNA polymerase to preferentially transcribe phage genes

160
Q

What do RNA phage do?

A

synthesise an RNA replicate to generate new progeny genomes

161
Q

What can phage egress occur by?

A

lysis, secretion, budding

162
Q

What have phages been used for?

A

anti-bacterial therapy , as an alternative to antibiotics (e.g. resistance)

163
Q

What are interferon?

A

Host proteins that stimulate antiviral immune response

164
Q

What are cloned IFN been used against?

A

persistent Hepatitis B

165
Q

What are 3 main problems for antiviral treatment?

A

Many virus infections, when clinical symptoms appear virus replication has peaked-too late for therapy.
As virus multiplication is so closely linked with cell processes, difficult to discriminate.
Selection of resistant mutants

166
Q

What do most antiviral drugs target?

A

Replicating (not latent) viruses

167
Q

What do ion channel blockers do?

A

Disrupt, preventing uncaring of enveloped viruses

168
Q

What is herd immunity?

A

The principle of vaccination whereby enough members of a population are immunised (e.g.90%), and thus the number of susceptible individuals is so low, that spread of a disease is slowed down, and eventually stops

169
Q

Give a example of recombinant virus vaccine?

A

vaccinia expressing measles protein

170
Q

What is a live vaccine?

A

Attenuated pathogenic viruses

171
Q

What is a dead vaccine?

A

Inactivated (UV, formalin etc) pathogenic viruses

172
Q

What is vaccination?

A

The artificial induction of immunity or immunisation with an immunogen.

173
Q

How does a vaccine cause immune memory?

A

Caused in B (antibodies) and T (cell-mediated )cells . later exposure to the immunogen results in recognition and more effective immune response

174
Q

What is the family name for small pox?

A

Poxviridae

175
Q

What type of virus is small pox?

A

Enveloped, helical, dsDNA 186kbp, 180+ genes

176
Q

What is the host of smallpox and the portal of entry?

A

Human. Inhalation/ingestion through direct contact with body fluids. It targets the epithelium via virus in blood

177
Q

What are symptoms of smallpox?

A

10-12 days postinfection flu-like , later pimples/vacuoles spread over body., more macules, more fatalities through fluid loss, opportunistic infections
Some individuals exhibit haemorrhagicsmallpox- skin, eyes, organs results in a high mortality

178
Q

What are prisons and viroids?

A

Unconventional infectious agents

179
Q

What are prions?

A

Infectious proteins that cause a group of diseases of the brain and nervous system called transmissible spongiform encephalopathies (TSEs)

180
Q

what are viroids?

A

Small, pathogenic RNAs that cause viruslike diseases in plant

181
Q

What can TSEs lead to?

A

Dementia, ataxia, paralysis, wasting and death

182
Q

What do viroids consist of?

A

Few 100 bases ssRNA (that do not encode proteins) and have Ni protein coat.

183
Q

What is Creutzfeld-Jacob Disease (CJD) causes by?

A

TSEs and some cases of CJD are hereditary

184
Q

What is the incubation time of CJD?

A

Long incubation time of yrs

185
Q

What is the first human disease to be eradicated?

A

Smallpox

186
Q

How did Edward Jenner find a cure for smallpox?

A

Milkmaids concerted cow pox not smallpox. Took pus from inoculated boy and he was exposed to smallpox but got no disease. Leading to vaccination

Biosciences (6 decks)

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