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Virology Flashcards

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Biology 101 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
Q

how can capsids form a flat sheet?

A

pack together in a hexagonal array

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26
Q

how can the hexagonal array be modified to enclose 3D space?

A

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

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27
Q

where is the nucleic acid genome located within helical symmetry viruses?

A

wound around the inside of the cylinder

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28
Q

how many pentagons are required to enclose a spherical space?

A

12

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29
Q

why are simple shapes used in virus capsids?

A

reduced number of proteins required which frees up space on the genome

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30
Q

what is a icosahedron?

A

no hexagons present in structure - may be formed of triangles

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31
Q

what do capsins provide as well as protection of nucleic acids?

A

attachment sites for cells
direction of virus to replication area
attack point for anti-viral immune response

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32
Q

what extra external structure do some viruses have?

A

lipid envelope

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33
Q

what does the lipid envelope surround?

A

capsule

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34
Q

how is a lipid envelope derived?

A

budding from different lipid bi-layers in the host cell

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35
Q

what type of viruses in animals all have an envelope?

A

all helical viruses

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36
Q

what type of viruses in animals mostly have an envelope?

A

many icosahedral viruses

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37
Q

what is a benefit of an envelope to the virus?

A

hides virus from the host

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38
Q

what is a disadvantage of an enveloped virus?

A

susceptible to damage by soap and detergent

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39
Q

what is a benefit of unenveloped viruses?

A

survive better in the environment

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40
Q

what are peplomers?

A

membrane anchored glycoproteins

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41
Q

in formation of peplomers what are sugars added to glycoproteins by?

A

host cell enzymes in the golgi apperatus

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42
Q

what is the role of peplomers?

A

adhere to host cell
influence pathology
target for immune system

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43
Q

what is the usual size range of viruses?

A

20-300 nM

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44
Q

what are the 5 genome types of viruses?

A 
dsDNA
ssDNA
dsRNA
\+ssRNA
-ssRNA
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45
Q

what do viruses utilise in order to replicate?

A

host organelles and nucleotides

46
Q

where are peplomer anchored?

A

envelope

47
Q

what are the 2 types of protein capsid symmetry?

A

helical or icosahedral

48
Q

what are the 7 steps of viral replication?

A 
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
Q

where does viral replication take place?

A

in host cells

50
Q

what does the virus do on entry to host cell?

A

shuts down normal cell working and new virus protiens are syntheised

51
Q

what happens during the attachment phase?

A

binding to cellular receptor of suitable host cell

52
Q

what is the ligand (attachment protein) of unenveloped viruses?

A

capsid proteins

53
Q

what is the ligand (attachment protein) of enveloped viruses?

A

envelope glycoproteins

54
Q

what does the attachment define?

A

tropism of the virus

55
Q

what is the tropism of a virus?

A

specificity of a virus for particular host tissue

56
Q

what is the tropism of a virus determined by?

A

interaction of viral surface structures with host cell receptors

57
Q

what happens during the entry of a virus?

A

the bound virus is endocytosed

58
Q

what happens during uncoating of the virus particle?

A

genome exits capsule and spreads to the site of replication

59
Q

what does acidification of the host cell environment cause?

A

conformational change in virus capsid which releases virus genome

60
Q

what does acidification do to the capsid?

A

creates a pore in the membrane through which the genome escapes into the cytoplasm

61
Q

where does virus assembly take place?

A

in cytoplasm or ER

62
Q

what 2 ways may the virus exit the host cell?

A

lysis

budding

63
Q

how long does viral replication in a host cell take?

A

3 hours

64
Q

what are the 5 key properties of viruses?

A 
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
Q

define pathogenesis

A

the process by which viruses causes disease

66
Q

what is the route of infection of a virus?

A

route of entry into the host

67
Q

what are the main routes of viral infection?

A 
respiratory 
oral
cutaneous
percutaneous
sexually transmitted
68
Q

what does the respiratory route of viral infection lead to?

A

localised respiratory disease

69
Q

what cells are targeted by respiratory route of viral infection?

A

ciliated epithelial cells of the upper respiratory tract

70
Q

what is the result of respiratory route of viral infection?

A

inflammation and reduced removal of microorganisms

71
Q

how is inflammation caused during respiratory viral infection?

A

damaged cells release inflammatory mediators which lead to altered blood flow and increased sensitivity

72
Q

how is reduced removal of microorganisms caused during respiratory viral infection?

A

due to damage to cilia that are unable to remove mucus from the lungs - can lead to secondary infection

73
Q

what type of infections are the most common cause of diarrhoea?

A

viral infections

74
Q

what cells are affected in diarrhoea?

A

enterocytes - causes diminished absorption of salts and water in small intestine

75
Q

why can there be rapid recovery from viral diarrhoea if dehydration and acidosis corrected?

A

crypts of small intestine are intact

76
Q

what are 3 types of percutaneous injection viral infection?

A

bites from infected animals
bites from insect vectors
aeatrogenic

77
Q

what is viraemia?

A

virus within the blood

78
Q

what can aeatrogenic viral infection be caused by?

A

dirty needles

79
Q

what is the first step of viral infection?

A

receptor/ligand binding between virus and host cell

80
Q

how can receptor/ligand binding affect the specificity of the virus to host and cells?

A

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
Q

what are the 2 types of receptor/ligand binding?

A

specific interactions

non-specific ligand

82
Q

describe specific interaction receptor/ligand binding

A

receptor/ligand interaction depends on exact complementary fit. The virus exactly matches it’s host cell

83
Q

what happens during HIV/FIV?

A

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
Q

what is the host potential of non-specific ligands?

A

wide range of host potentials

85
Q

what does influenza haemagglutinin bind to on body cells?

A

sialic acid

86
Q

what is sialic acid?

A

glycoprotein found on many cell surfaces

87
Q

how is the route of infection in influenza limited to the respiratory tract?

A

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
Q

what can alter host specificity for infection and severity of disease?

A

a single amino acid change to the cleavage site

89
Q

what is the outcome of the disease determined by?

A

function of the infected cell

90
Q

what is lytic infection?

A

acute virus infection resulting in cell death accompanied by release of new virus particles

91
Q

what is a cytopathic virus?

A

one which results in cell death

92
Q

what does the release of virus from one cell cause?

A

infection of many thousands of new cells leading to extensive loss of cell function

93
Q

what are latent infections?

A

virus infections which persist within a cell and do not cause cell death (herpes)

94
Q

how long can latent virus infections last for?

A

the lifetime of the host

95
Q

what is the effect of latent viral infections on the cell?

A

alter the rate of cell division and growth

96
Q

how are virus particles released from cells in latent infection?

A

periodically without killing the cell, usually through budding

97
Q

what occurs during persistent viral infection?

A

the immune system fails to clear infection leading to continual shedding of the virus by cells and production of viral proteins

98
Q

how do viruses modify the function of the cell?

A

increase cell division leading to cell growth and tumor formation

99
Q

what is the typical host response to viral infection in epithelial cells?

A

inflammatory response in cells an adjacent tissues

100
Q

what factors are produced by epithelium following viral infection?

A

interferon
pro inflammatory cytokines
chemokines

101
Q

what pro inflammatory cytokines are released in response to viral infection?

A

IL1, IL6 and IL8

102
Q

what is the role of chemokines?

A

attract leukocytes to enhance immune response

103
Q

how is a fever caused during viral infection?

A

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
Q

what endogenous pyrogens are used to fight viral infection?

A

interferon

TNF-alpha

105
Q

what is sickness behaviour?

A

motivational state responsible for re-organising perceptions and actions to enable ill individuals to cope better with infection

106
Q

what behaviours are involved in sickness behaviour?

A 
decreased motor activity
social withdrawal
reduced responsiveness
reduced food and water intake
increased slow wave sleep
altered cognition
increased pain sensitivity
107
Q

what factors are responsible for sickness behaviour?

A

IL1 and IFN

108
Q

what is the role of interferon alpha?

A

bind to specific receptors on neighboring cells to prevent them becoming infected

109
Q

how does interferon alpha prevent cells becoming virally infected?

A

binding induces synthesis of antiviral proteins

110
Q

what produces interferon alpha?

A

virally infected cells

X Pre Clinical Science (17 decks)

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