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Virology Flashcards

1
Q

what was the first indication of the presence of viruses?

A

foot and mouth disease would be transmitted even after being passed through bacteria free filtrate (which would kill bacteria)

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2
Q

how were mammalian viruses shown to be corpuscular?

A

dilution experiments - severity of symptoms did not reduce with dilution but the number of cases did

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3
Q

where is the only place that viruses can grow?

A

in living tissue

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4
Q

what did the use of embryonated eggs to grow viruses lead to?

A

identification of human viruses and lead to production of vaccines

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5
Q

what are the 7 key impacts of molecular biology on our understanding of viruses and viral disease?

A 
scientific basis for classification
understanding replication and pathogenesis (infection)
development of antiviral drugs
production of vaccines
understanding viral evolution
new diagnostic tests
molecular epidemiology of viruses
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6
Q

how can the relationship of viruses with host cells be described?

A

viruses are obligate, intracellular parasites

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7
Q

what are viruses dependent on the host cell for?

A

source of energy

provision of raw materials

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8
Q

what do viruses use host cell machinery for?

A

to replicate genome

to synthesise new protein

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9
Q

describe the formation of protein from DNA

A

DNA is transcribed to RNA. Introns are removed through splicing and a cap and tail are added - mRNA is formed. mRNA is translated to a polypeptide by ribosomes. The polypeptide is then folded to form the protein

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10
Q

what is the virus genome formed of?

A

nucleic acids

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11
Q

what is the size of a viral genome?

A

small - only a few genome protein components

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12
Q

what is not included in a viral genome?

A

no protein synthesis enzymes or ribosomes
no genes for lipid or amino acid synthesis
few or no introns (non - coding DNA)

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13
Q

why is there little/none non-coding DNA (introns) in a virus genome?

A

less need for control sequences as DNA is less complex than in mammals

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14
Q

how does the virus perform functions that it does not possess DNA code for?

A

they are supplied by host cells

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15
Q

what DNA genome can be found in viruses?

A

double strand DNA (dsDNA)

single strand DNA (ssDNA)

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16
Q

what RNA genome do many viruses have?

A

positive sense single stranded RNA
negative sense single stranded RNA
double stranded RNA

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17
Q

what happens to positive sense single stranded RNA once in the host cell?

A

directly translated to protein

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18
Q

what happens to negative sense single stranded RNA once in the host cell?

A

only translated to protein once it has been copied to positive sense RNA

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19
Q

what must be supplied by the virus if it has negative sense single stranded RNA?

A

RNA polymerase

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20
Q

what is virus nucleic acid enclosed within?

A

a capsid

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21
Q

what is a capsid?

A

protein coat which encloses virus genome

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22
Q

what is a capsid formed of?

A

multiple protein subunits known as capsomers

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23
Q

what are the 4 key roles of the capsid?

A

packaging of genome and essential enzymes
protection of nucleic acid from UV light
protection from nucleases
provides specificity for attachment of viruses

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24
Q

what do nucleic acid and capsid form together?

A

nucleocapsid

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25
how can capsids form a flat sheet?
pack together in a hexagonal array
26
how can the hexagonal array be modified to enclose 3D space?
rolled into a cylinder where units form a new spiral pattern (helical symmetry) pentagons placed within the sheet to produce gaps - when closing these gaps a spherical space is enclosed
27
where is the nucleic acid genome located within helical symmetry viruses?
wound around the inside of the cylinder
28
how many pentagons are required to enclose a spherical space?
12
29
why are simple shapes used in virus capsids?
reduced number of proteins required which frees up space on the genome
30
what is a icosahedron?
no hexagons present in structure - may be formed of triangles
31
what do capsins provide as well as protection of nucleic acids?
attachment sites for cells direction of virus to replication area attack point for anti-viral immune response
32
what extra external structure do some viruses have?
lipid envelope
33
what does the lipid envelope surround?
capsule
34
how is a lipid envelope derived?
budding from different lipid bi-layers in the host cell
35
what type of viruses in animals all have an envelope?
all helical viruses
36
what type of viruses in animals mostly have an envelope?
many icosahedral viruses
37
what is a benefit of an envelope to the virus?
hides virus from the host
38
what is a disadvantage of an enveloped virus?
susceptible to damage by soap and detergent
39
what is a benefit of unenveloped viruses?
survive better in the environment
40
what are peplomers?
membrane anchored glycoproteins
41
in formation of peplomers what are sugars added to glycoproteins by?
host cell enzymes in the golgi apperatus
42
what is the role of peplomers?
adhere to host cell influence pathology target for immune system
43
what is the usual size range of viruses?
20-300 nM
44
what are the 5 genome types of viruses?
``` dsDNA ssDNA dsRNA +ssRNA -ssRNA ```
45
what do viruses utilise in order to replicate?
host organelles and nucleotides
46
where are peplomer anchored?
envelope
47
what are the 2 types of protein capsid symmetry?
helical or icosahedral
48
what are the 7 steps of viral replication?
``` attachment to plasma membrane entry into cytoplasm/nucleus un-coating of virus particle synthesis of mRNA and protein replication of nucleic acid virus assembly exit of virus from cell ```
49
where does viral replication take place?
in host cells
50
what does the virus do on entry to host cell?
shuts down normal cell working and new virus protiens are syntheised
51
what happens during the attachment phase?
binding to cellular receptor of suitable host cell
52
what is the ligand (attachment protein) of unenveloped viruses?
capsid proteins
53
what is the ligand (attachment protein) of enveloped viruses?
envelope glycoproteins
54
what does the attachment define?
tropism of the virus
55
what is the tropism of a virus?
specificity of a virus for particular host tissue
56
what is the tropism of a virus determined by?
interaction of viral surface structures with host cell receptors
57
what happens during the entry of a virus?
the bound virus is endocytosed
58
what happens during uncoating of the virus particle?
genome exits capsule and spreads to the site of replication
59
what does acidification of the host cell environment cause?
conformational change in virus capsid which releases virus genome
60
what does acidification do to the capsid?
creates a pore in the membrane through which the genome escapes into the cytoplasm
61
where does virus assembly take place?
in cytoplasm or ER
62
what 2 ways may the virus exit the host cell?
lysis | budding
63
how long does viral replication in a host cell take?
3 hours
64
what are the 5 key properties of viruses?
``` small intracellular parasites grow only in living cells genomes of RNA or DNA no genes for energy metabolism genomes are replicated and new virus proteins are made using host cell machinery ```
65
define pathogenesis
the process by which viruses causes disease
66
what is the route of infection of a virus?
route of entry into the host
67
what are the main routes of viral infection?
``` respiratory oral cutaneous percutaneous sexually transmitted ```
68
what does the respiratory route of viral infection lead to?
localised respiratory disease
69
what cells are targeted by respiratory route of viral infection?
ciliated epithelial cells of the upper respiratory tract
70
what is the result of respiratory route of viral infection?
inflammation and reduced removal of microorganisms
71
how is inflammation caused during respiratory viral infection?
damaged cells release inflammatory mediators which lead to altered blood flow and increased sensitivity
72
how is reduced removal of microorganisms caused during respiratory viral infection?
due to damage to cilia that are unable to remove mucus from the lungs - can lead to secondary infection
73
what type of infections are the most common cause of diarrhoea?
viral infections
74
what cells are affected in diarrhoea?
enterocytes - causes diminished absorption of salts and water in small intestine
75
why can there be rapid recovery from viral diarrhoea if dehydration and acidosis corrected?
crypts of small intestine are intact
76
what are 3 types of percutaneous injection viral infection?
bites from infected animals bites from insect vectors aeatrogenic
77
what is viraemia?
virus within the blood
78
what can aeatrogenic viral infection be caused by?
dirty needles
79
what is the first step of viral infection?
receptor/ligand binding between virus and host cell
80
how can receptor/ligand binding affect the specificity of the virus to host and cells?
depending on specificity the virus may only be able to bind to one type of cell in a single host. Others can bind to a much wider range
81
what are the 2 types of receptor/ligand binding?
specific interactions | non-specific ligand
82
describe specific interaction receptor/ligand binding
receptor/ligand interaction depends on exact complementary fit. The virus exactly matches it's host cell
83
what happens during HIV/FIV?
specific binding to CD4 T-cells, leads to immune deficiency. HIV cannot infect cats and FIV cannot infect humans even though the disease is the same due to specific interactions
84
what is the host potential of non-specific ligands?
wide range of host potentials
85
what does influenza haemagglutinin bind to on body cells?
sialic acid
86
what is sialic acid?
glycoprotein found on many cell surfaces
87
how is the route of infection in influenza limited to the respiratory tract?
infection of cells depends on protease cutting the virus peplomer. Not all cells possess this enzyme so the virus is unable to infect them
88
what can alter host specificity for infection and severity of disease?
a single amino acid change to the cleavage site
89
what is the outcome of the disease determined by?
function of the infected cell
90
what is lytic infection?
acute virus infection resulting in cell death accompanied by release of new virus particles
91
what is a cytopathic virus?
one which results in cell death
92
what does the release of virus from one cell cause?
infection of many thousands of new cells leading to extensive loss of cell function
93
what are latent infections?
virus infections which persist within a cell and do not cause cell death (herpes)
94
how long can latent virus infections last for?
the lifetime of the host
95
what is the effect of latent viral infections on the cell?
alter the rate of cell division and growth
96
how are virus particles released from cells in latent infection?
periodically without killing the cell, usually through budding
97
what occurs during persistent viral infection?
the immune system fails to clear infection leading to continual shedding of the virus by cells and production of viral proteins
98
how do viruses modify the function of the cell?
increase cell division leading to cell growth and tumor formation
99
what is the typical host response to viral infection in epithelial cells?
inflammatory response in cells an adjacent tissues
100
what factors are produced by epithelium following viral infection?
interferon pro inflammatory cytokines chemokines
101
what pro inflammatory cytokines are released in response to viral infection?
IL1, IL6 and IL8
102
what is the role of chemokines?
attract leukocytes to enhance immune response
103
how is a fever caused during viral infection?
production of endogenous pyrogens binding to opioid receptors on the hypothalamus activation of COX-2 in the hypothalamus leading to increased prostaglandin secretion altered firing of temperature sensitive neurons in the anterior hypothalamus increase in whole body temperature
104
what endogenous pyrogens are used to fight viral infection?
interferon | TNF-alpha
105
what is sickness behaviour?
motivational state responsible for re-organising perceptions and actions to enable ill individuals to cope better with infection
106
what behaviours are involved in sickness behaviour?
``` decreased motor activity social withdrawal reduced responsiveness reduced food and water intake increased slow wave sleep altered cognition increased pain sensitivity ```
107
what factors are responsible for sickness behaviour?
IL1 and IFN
108
what is the role of interferon alpha?
bind to specific receptors on neighboring cells to prevent them becoming infected
109
how does interferon alpha prevent cells becoming virally infected?
binding induces synthesis of antiviral proteins
110
what produces interferon alpha?
virally infected cells

X Pre Clinical Science (17 decks)

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