Viruses Flashcards
(187 cards)
0
Q
Do viruses grow or divide?
A
No
1
Q
How small of viruses?
A
nm in size
2
Q
What are viruses?
A
Agents that can pass through filters that trap most known bacteria
3
Q
What are viruses able to infect?
A
Most living organism, animals, plant, fungi, bacteria
4
Q
What are common features viruses share?
A
Have a protein coat, capsid- encapsulating the genetic material
5
Q
What is a virion?
A
A whole virus particle
6
Q
What percentage of protein are viruses composed of?
A
50-90%
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)
8
Q
Why are capsid symmetrical in appearance?
A
Due to precise assembly of repeated protein sununits
9
Q
Why are capsid symmetrical in appearance?
A
Due to precise assembly of repeated protein subunits
10
Q
What are virus particles held together by?
A
Hydrophobic and electrostatic interactions (not covalent bonds)
11
Q
What are the 2 main classes of virus capsid structure?
A
Helical and icosahedral symmetry
12
Q
What are the properties of virus particles?
A
Protection Recognition Self- assembly Fidelity Economy
13
Q
What are virus capsids composed of?
A
Proteins. Proteins fold into nonsymmertical (tertiary) structures
14
Q
What are the two ways asymmertcial subunits can form particles?
A
Helical and cubical
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
16
Q
What symmetry does a tobacco mosaic virus have?
A
Helical symmetry producing a rod shaped capsid
17
Q
What symmetry does Poliovirus have?
A
Icosahedral capsid (of 3 different proteins)
18
Q
What do both type of capsid have?
A
A surrounding lipid envelope, derived form the host cell membrane
19
Q
What does virus particle contain?
A
Capsid
nucleiocapsid
20
Q
What are the two types of viruses?
A
Enveloped and naked (non-enveloped)
21
Q
What is the capsid called in a enveloped virus?
A
nucleocapsid
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.
23
Q
What can envelope make viruses appear?
A
non-symmetrical shapes
Or
pleomorphic (change shape)
24
What are between the nucleocapsid and envelope?
tegument or matrix proteins which often link the nucliocapsid and envelope
25
What can viruses genomes be?
DNA or RNA, and either double or single-stranded
26
What is a nucleocapsid?
the capsid of a virus with the enclosed nucleic acid.
27
What are the two types of viral shapes?
Icosahedral and helical
28
What does virus classification take in to account?
Genome type
Capsid structure
Disease pathology ect.
29
What is the classification system of viruses?
Species
Genus
subfamily
Family
30
What are the major virus groups based on genetic material?
dsDNA, ssDNA, dsRNA, ssRNA
31
What can the RNA genomes produce?
Proteins with no DNA involved
32
What can ssRNA be divided into?
Positive or negative sense
33
What are proteins produced directly form?
Positive sense RNA
34
What does negative sense RNA need to be copied into before a protein can be produced?
Negative sense RNA needs to be copied into positive sense first
35
Which two types of genetic material viruses uses reverse transcriptase enzyme in their replication?
ssRNA and dsDNA
36
What are the seven classes of virus according to the Baltimore Classification ?
```
dsDNA
ssDNA
dsRNA
+ssRNA
-ssRNA
RNA reverse transcribing viruses
DNA reverse transcribing viruses
```
37
What is the pathology of viral disease caused by?
Toxicity of virus gene products on cell metabolism.
Reactions of host to infected cells.
Modification of cell function by virus gene products
38
What must a virus do in order to multiply?
infect a susceptible cell at the portal of entry
39
What are the steps when a virus enters a cell?
Transferring genetic material- essential proteins.
| Viral genes lead to production of viral proteins
40
What does production of viral proteins in host cell ensure?
Replication of genome
Packaging genome into virions
Effect structure and/or function of infected cell
41
What do viruses rely on during replication?
Depending on number of viral genes they depend on host proteins during replication
42
What is progeny?
An organism produced as a result of replication. New progeny viruses are released form cell
43
What is a bacteriophage?
a virus which parasitizes a bacterium by infecting it and reproducing inside it.
44
What is the eclipse phase?
The period of time between infection by a virus and the appearance of the mature virus within the cell.
45
What happens following infection?
And for few hours (eclipse phase), only parental virus is detectable. Virus genome exposed, gene expressed, interact with cell proteins.
46
What happens in the maturation and release phase?
Progeny virus builds up in the cell exponentially and either causes the cell to burst (lysis) or bud out through the cell membrane
47
How much do virus release and cycle?
Release 1-100k and cycle 8-72h
48
What are the three types of infection by a virus?
Productive
Restrictive
Abortive
49
What does permissive cells mean?
that the virus is able to circumvent host defences and is able to replicate
50
What does the productive infection involve?
Permissive cells
51
what does the restrictive infection involve?
Partly permissive cell or cell population
52
What does abortive cells involve?
Non- permissive cell (not all virus genes expressed) virus lacks some genes
53
What some viruses have in regards to productive infection?
Short (acute)
Long (persistent)
They go into the lytic cycle
54
What can viruses enter if the stimulus to enter the lytic cycle is absent?
A non-lytic cycle or lysogency
55
What was the first example a lytic infection carried out by?
A bacteriophage of e.coli called lambda
56
What is lysogenic infection?
A typical of non-bacterial viruses
57
What is a latent infection?
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
58
Give example of viruses in which latent infection occurs?
herpesviruses,HIV-1 and some parvoviruses
59
How can virus genome be maintained in a host?
Interfaced in host DNA or as free episome
60
What does attachment involve?
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.
61
What is the penetration step?
A fast, energy-dependent step
62
How do non-enveloped viruses enter during the penetration step?
Directly across the membrane via endocytosis into cytoplasmic vacuoles
63
How do enveloped viruses enter during the penetration step?
The envelope and the cell membrane fuse (via protein: receptor interaction) allowing the nucleocapsid to enter the cell
64
What is uncoating?
Where the vision fully or partially disintegrates (sometimes aided by cell enzymes; acid pH in endoscopes often critical) exposing viral genome
65
What is the central dogma in a protein?
Replication, transcription and translation
| DNA-RNA-Proteins
66
What two events are critical to viral infection?
The production of virus structural proteins and enzymes
| The replication of the viral genome (dsDNA, ssDNA, dsRNA, ssRNA)
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What happens after uncoating?
Gene expression, genome replication and progeny assembly
68
What does DNA need to transcribed into?
mRNA, that is then translated into proteins
69
Where do most events take place for a herpesvirus?
The nucleus
70
Where do most events take place for a poxviruses?
The cytoplasm
71
What shape genome is RNA viruses?
linear
72
What is viral genome integrated as in the hosts chromosome?
cDNA
73
What do non enveloped viruses undergo?
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)
74
What does maturation involve in enveloped viruses?
Inserting viral glycoproteins in a cell membrane. This is usually the outer membrane
75
What do the glycoproteins interact with in enveloped viruses?
With nucleocapsid pulling the membrane around it. The mature virio the. Buds out of the cell during egress
76
What does the insertion of glycoproteins I the outer membrane make?
The infected cell a target for the host immune system
77
What do the number of genes in a viruses vary from?
10100
78
What are viruses have though to have originated from?
Either degenerate cells or from break away cell genetic material able to replicate
79
Can virus DNA be mutated?
Yes
80
Why is RNA particularly mutable?
As its not proofread during synthesis unlike DNA
81
What is antigenic drift?
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
What can genome segment reassortment lead to?
New strains via antigenic shift
83
What is the family of the influenza virus?
Orthomyxoviridae
84
What type of virus is influenza virus?
Enveloped, pleomorphic; -negative sense ssRNA
| In 8 segments (1-2kbp)
85
What does influenza virus affect?
Specific mammals
| But type A host birds are natural reservoir in wild aquatic birds
86
What is the portal entry of influenza virus and target cells?
Epithelial mucosa via aerosol
| Targets lower respiratory tract
87
What are the symptoms and pathology of influenza?
Cough,fever, acute infection
| Pathology is epithelial cells, pneumonia
88
What are envelope spike do?
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
What is the most important antigen?
Haemagglutinin- protective antibodies raised against HA
90
What does drift require in regards to vaccines?
For vaccines to be produced every season based on the latest circulating strain in the other hemisphere of the globe
91
What can shift result in?
A pandemic e.g. Swine flu
92
What are killed vaccines?
Where isolates are inactivated or detergent treated to release H and N proteins
93
What are antiviral drugs used to treat?
Early infections e.g. Neuraminidase analogues osteltamivir which competitively inhibits NA cleaving HA from sialic acid, reducing viral egress
94
What is the family of herpes simplex virus?
herpersviridae
95
What type of virus is herpes simplex virus?
Enveloped, icosahedral, linear dsSNA, 70 genes, circularises in cell
96
What is the target host for herpes simplest and what is the portal of entry?
Skin or epithelial mucosa via saliva. It targets cells is neurons: axon- dorsal root ganglia
97
What are symptoms and pathology of herpes simplex?
Nerve tingling on reactivation the pathology is epithelial blisters (cold sores) sometimes eye infections or encephalitis. Acute infection-latency
98
What causes reactivation of herpes simplex virus from latency?
immunocompromised and this produces local blisters
99
When do enveloped spikes of herpes simplex bind to?
Envelope spikes of Glycoprotein (gC) bind to heparin sulphate proteoglycan on cell
100
What controls the extent of the infection caused herpes simplex?
humoral (antibody) and cell-mediated immune response control the extent of infection
101
What are herpetic diseases caused by HSV-1?
Cold sores of the mouth
Lesions on the lip
Herpes keratitis of the eye
Herpes infection- from contact sports
102
What are 90% of herpes diseases caused by?
HSV-2
103
What percentage of cases does HSV-1 cause gential herpes?
10%
104
What is the treatment of herpes simplex virus (HSV)?
No vaccine but nucleoside analogues antiviral drugs such as ACV are used
105
What activates ACV?
HSV thymidine kinase gene(TK)
106
What is TK involved in?
Nucleoside synthesis for DNA
107
Why can't HSVTK uses ACV as a substrate?
HSVTK has evolved substantially differently than human TK
108
What does HSVTK convert ACV to?
ACV-monophosphate. Cell kinase enzymes add another 2 phosphates
109
How is ACV-triphosphate incorporated into viral DNA?
Preventing replication- acutely infected cells die, but not latent infections as HSVTK gene not expressed during latency
110
What is chickenpox caused by?
varicella zoster virus
111
What does Epstein-Barr virus cause?
80% cases of infectious mononucleosis/glandular fever. leads to cancer in some individuals
112
What does cytomegalovirus cause?
Produces 20% infectious mononucleosis then dormancy. Reactivation in immunocompromised
113
How is herpesvirus destroyers in the environment?
Its fragile and easily disrupted by heat, dedication. 70% alcohol, soap and detergent
114
Why is herpesvirus sensitive to the environment?
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
What is Kaposi sarcoma-associated virus detected in?
All Kaposis sarcomas, an aggressive pigmented sarcoma of the skin.
116
What is Kaposi virus transmitted by?
Saliva, its easily diagnosed by biopsy. It is an earliest manifestation of AIDS
117
What is the family of papillomavirus?
papilomaviridae
118
What type of virus is the papillomavirus?
Non- enveloped, icosahedral, circular, dsDNA 8kb, 9 genes
119
What is the host for papillomavirus?
Specific types infect birds, mammals
120
What is the portal of entry for the papillomavirus?
Small wounds in skin or mucosa via direct contact
121
What is the pathology of papillomavirus?
Benign tumours, cervical cancer. Some infect oncogenic. Acute infection to latency where reactivation is caused by immunocompromised.
122
What do the envelope spikes on the virus bind to?
Heparin sulphate proteoglycan on cell
123
What 2 papillomavirus gene products inacrivate the cells tumour suppressor proteins p53 and Rb?
E6 and E7 respectively. Causing cell growth- benign/ premalignant tumours.
124
What do Gardasil and Cervarix vaccines consist of?
purifies L1 capsid protein
125
What is the family name of the Poliovirus?
picornoviridae
126
What type of virus is Poliovirus?
A non-enveloped, icosahedral, + sense ssRNA, 7.5kb encodes a single polyprotein that is cleaved into 10 polypeptides
127
What is the host of the Poliovirus and the portal of entry?
Human. Oral via rascally contaminated water or food. Infects epithelium of pharynx and gut. It targets epithelium and blood cells
128
What are the symptoms and pathology of Poliovirus?
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
What does vision protein 1 interact with?
Poliovirus receptor (PVR) an immunoglobulin glycoprotein on cell surface
130
Where does replication of the Poliovirus occur?
In cytoplasm via viral RNA-dependent RNA polymerase.
131
What does asymptomatic mean?
Producing no symptoms
132
What % of Poliovirus infections are asymptomatic?
95%
133
What asymptomatic people able to do?
shed virus in stool and are able to transmit the virus to others
134
What % of Poliovirus infections produce mild symptoms?
4-8%
135
What are mild symptoms of Poliovirus infection?
```
Malaise
Gastrointestinal distress
Fever
Influenza-like illness
sore throat
Recovery within a week
```
136
What % of Poliovirus infections cause major illness?
Less than 1%
137
What are major symptoms of Poliovirus?
Flaccid paralysis- weakness
Inflammation and sometimes destruction of neurons
Recovery can take up to two years and may be incomplete
138
What is the vaccine of Poliovirus?
Formalin-inactivated dead vaccine of the three Poliovirus serotypes
139
What is the oral live vaccine of Poliovirus?
non-virulent, attenuated strain
140
How is Poliovirus attenuated?
By serial passage in cell culture- enriches weaker mutated viruses
141
What does the vaccines stimulate?
Neutralising antibody production
142
What can some attenuated viruses revert to?
Virulence when passes through the gut (1 in a million cases)
143
What is the family of the Human immunodeficiency virus 1?
retroviridae
144
What type of virus is HIV 1?
Enveloped, helical, 2 genome copies of positive sense ssRNA, 10kb, 9 genes
145
What is the host, portal of entry and target cells of HIV 1?
Humans. Mucosa via fluids, blood
| Targets CD4+ T cells, macrophages
146
What are symptoms and pathology of HIV 1?
Fever, malaise, lymph node swelling.
Pathology: depletion of CD4+ cell count leads to acquired immunodeficiency syndrome (AIDS) and opportunistic infections and death
147
What do enveloped gp120 glycoprotein bind to?
CD4 molecules or chemokine receptors on cell. Though that dendritic cells at portal site are infected then pass virus onto T cells/macrophages
148
What does the reverse transcriptase convert?
ssRNA to dsDNA which is integrated into cell genome vain viral integrase
149
What happens after initial cute infection of HIV 1?
Get latency for weeks to years
150
What are treatments for HIV 1?
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
What is the oncogene virus?
Rous Sarcoma
| Led to discovery of Arc gene- a protein kinase gene
152
What can retrovirus alter?
TS or proto-oncogene expression by integration of their genome into cell DNA
153
What are bacteriophage?
Viruses that infect bacteria
154
What family is bacteriophage from?
Siphoviridae
155
What is the genome of bacteriophage?
dsDNA genome and some RNA
156
What is the virion structure of a bacteriophage?
Tail fibres bind to cell surface receptors , then pins, then DNA injected into host
157
What life cycles do bacteriophage have?
Lytic, lysogenic
158
What happens in lysogeny of a bacteriophage?
prophages integrate in host genome or exist episomally, receiving into lytic cycle under certain conditions.
159
What happens in lytic cycle of bacteriophage?
Viral proteins may modify cell RNA polymerase to preferentially transcribe phage genes
160
What do RNA phage do?
synthesise an RNA replicate to generate new progeny genomes
161
What can phage egress occur by?
lysis, secretion, budding
162
What have phages been used for?
anti-bacterial therapy , as an alternative to antibiotics (e.g. resistance)
163
What are interferon?
Host proteins that stimulate antiviral immune response
164
What are cloned IFN been used against?
persistent Hepatitis B
165
What are 3 main problems for antiviral treatment?
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
What do most antiviral drugs target?
Replicating (not latent) viruses
167
What do ion channel blockers do?
Disrupt, preventing uncaring of enveloped viruses
168
What is herd immunity?
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
Give a example of recombinant virus vaccine?
vaccinia expressing measles protein
170
What is a live vaccine?
Attenuated pathogenic viruses
171
What is a dead vaccine?
Inactivated (UV, formalin etc) pathogenic viruses
172
What is vaccination?
The artificial induction of immunity or immunisation with an immunogen.
173
How does a vaccine cause immune memory?
Caused in B (antibodies) and T (cell-mediated )cells . later exposure to the immunogen results in recognition and more effective immune response
174
What is the family name for small pox?
Poxviridae
175
What type of virus is small pox?
Enveloped, helical, dsDNA 186kbp, 180+ genes
176
What is the host of smallpox and the portal of entry?
Human. Inhalation/ingestion through direct contact with body fluids. It targets the epithelium via virus in blood
177
What are symptoms of smallpox?
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
What are prisons and viroids?
Unconventional infectious agents
179
What are prions?
Infectious proteins that cause a group of diseases of the brain and nervous system called transmissible spongiform encephalopathies (TSEs)
180
what are viroids?
Small, pathogenic RNAs that cause viruslike diseases in plant
181
What can TSEs lead to?
Dementia, ataxia, paralysis, wasting and death
182
What do viroids consist of?
Few 100 bases ssRNA (that do not encode proteins) and have Ni protein coat.
183
What is Creutzfeld-Jacob Disease (CJD) causes by?
TSEs and some cases of CJD are hereditary
184
What is the incubation time of CJD?
Long incubation time of yrs
185
What is the first human disease to be eradicated?
Smallpox
186
How did Edward Jenner find a cure for smallpox?
Milkmaids concerted cow pox not smallpox. Took pus from inoculated boy and he was exposed to smallpox but got no disease. Leading to vaccination
