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viruses Flashcards

1
Q

what are viruses

A

simple acellular infection pathogens

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2
Q

what are viruses incapable of (compared to bacteria)

A

self-replication
- host
metabolic activity

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3
Q

what can viruses infect

A

every category of life

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4
Q

how big are viruses

A

20-200nm
- viruses that infect humans
too small for light microscopes

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5
Q

how is gene information stored in viruses

A

either RNA or DNA
either linear or circular
RNA - +ve sense (mRNA) or -ve sense (convert to +ve first)

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6
Q

what is the nucleocapsid

A

genome + capsid
- may also contain essential or accessory enzyme to facilitate initial replication
naked/ envlopes

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7
Q

what is a virion

A

fully assembled infection extracellular particle

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8
Q

what is the capsid comprised of

A

capsomeres
- several different polypeptides grouped together

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9
Q

what shapes can the capsid be

A

distinctive symmetry
helical/ icosahedral

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10
Q

give an example of an icosahedral virus

A

Hep B

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11
Q

what characterises an enveloped virus

A

phospholipid bilayer
- derived from the host cell
Golgi apparatus
ER
nuclear membrane

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12
Q

what is the envelope of an enveloped virus comprised of

A

lipids, virus proteins and glycoproteins

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13
Q

what are the host cell membrane proteins replaced by in viruses

A

virally encoded glycoproteins
- spike proteins

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14
Q

what are the spike proteins on influenzas called

A

Hemagglutinin and Neuraminidase

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15
Q

where are viral attachment proteins found

A

alongside capsid in naked viruses
anchored in the phospholipid bilayer of enveloped viruses

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16
Q

what is viral tropism

A

ability of a given virus to productively infect a
particular cell - cellular tropism
tissue - tissue tropism
host species - host tropism

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17
Q

what are the modes of transmission for a virus

A

oral transmission
droplet transmission
direct inoculation
sexual transmission
trans-placental
direct skin contact

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18
Q

how are orally transmitted viruses spread

A

contaminated food + drink; saliva

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19
Q

give an example of an orally transmitted virues

A

Hep A/ norovirus

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20
Q

how are droplet transmitted viruses spread

A

inhalation

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21
Q

give an example of a droplet transmitted virus

A

influenza
coronavirus
measles

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22
Q

how do directly inoculated viruses spread

A

injections; trauma; insect bites

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23
Q

give an example of directly inoculated virus

A

yellow fever/ zika

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24
Q

give an example of a sexually transmitted virus

A

HIV

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25
give an example of a virus spread by skin-skin contact
herpes
26
give an example of a single stranded +ve sense virus
ebola
27
what symptoms characterise a common cold
blocked or running nose, coughing and sneezing, headaches, sore throat
28
what symptoms characterise bronchoilitis
starts similarly to a cold but progresses to coughing/ wheezing/ difficulty breathing
29
what symptoms characterise croup
harsh brassy/ barking cough
30
give examples of respiratory illnesses
common cold, bronchiolitis, croup
31
give 3 examples of coronaviruses
SARs-CoV MERS-CoV SARS-CoV-2
32
what is a zoonose
a virus coming from an animal
33
list the types of influenza
A B C D
34
what types of influenza affects humans
A B
35
what are the symptoms of human influenza
fever, chills, headache, muscle pain, extreme fatigue, dry cough, sore throat, blocked nose
36
give three examples of human herpesviruses
measles mumps rubella
37
what type of virus is HIV
single stranded +ve sense RNA retrovirus
38
what CD4 count constitutes AIDS
220 cells/ mm3
39
list some common opportunistic infections
Epstein-Barr virus Fungal infections - oral candidiasis, Pneumocystis pneumonia HHV-8 virus (Kaposi's sarcoma) cytomegalovirus (CMV) retinitis cryptosporidium
40
give two ways that viruses enter a host cell
macropinocytosis, membrane fusion
41
describe micropinocytosis
taches to the host cell it can become engulfed by the host cell membrane
42
describe membrane fusion
virus inserts itself into the host cell
43
what are the stages of viral replication
attachment penetration uncoating replication assembly virion release - lysis/ budding
44
describe the attachment phase of viral replication
viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface - specificity determines the host range (tropism) of a virus
45
describe the penetration stage of viral replication
the process of attachment to a specific receptor can induce conformational changes in viral capsid proteins (/ lipid envelope) - results in the fusion of viral + CMs some DNA viruses can also enter the host cell through receptor-mediated endocytosis
46
describe the uncoating stage of viral replication
the viral capsid is removed and degraded by viral enzymes or host enzymes, releasing the viral genomic nucleic acid
47
describe the replication stage of viral replication
after the viral genome has been uncoated, transcription or translation of the viral genome is initiated - this stage differs greatly between DNA and RNA viruses + viruses with opposite polarity - culminates in the de novo synthesis of viral proteins and genome
48
describe the assemebly stage of viral replication
after de novo synthesis of viral genome and proteins, which can be post-transcriptionally modified, viral proteins are packaged with newly replicated viral genome into new virions that are ready for release from the host cell - also called maturation
49
describe the lysis approach to the virion release stage of viral replication
results in the death of an infected host cell viruses that cause this are referred to as cytotoxic
50
give an example of a virus that uses lysis
variola major (smallpox)
51
describe the budding approach to the virion release stage in viral replication
typically enveloped viruses (e.g. influenza A) acquisition of the viral phospholipid envelope viruses that cause this are referred to as cytopathic
52
describe what can happen after virion release
some viral proteins remain within the host's cell membrane - acts as a potential target for circulating antibodies - residual viral proteins that remain within the cytoplasms of a host cell can be processed and presented at CSM on MHC I
53
describe the RNA replication of dsRNA viruses
one strand is transcribed by viral polymerase into mRNA
54
describe the RNA replication of +ve sese ssRNA viruses
can be used directly as mRNA
55
describe the RNA replication of -ve sense ssRNA viruses
viral polymerase converts into +ve sense mRNA strand, which can then be used as mRNA
56
describe the RNA replication of retroviruses
-ve sense ssRNA -> -ve sense ssDNA (viral transcriptase enzyme) -> dsDNA -> enters nucleus -> integrated into host genome -> mRNA (host polymerase)
57
describe HIV replication
1- Nucleocapsids containing viral genome and enzymes enters the target cell 2- Viral reverse transcriptase catalyses reverse transcription of ssRNA to form RNA-DNA hybrids 3- To yield HIV dsDNA the viral RNA template is partially degraded by ribonuclease H and the second DNA strand is synthesized 4- Viral dsDNA is translocated into nucleus and integrated into the host genome by the viral integrase enzyme 5- Transcription factors transcribe the proviral DNA into genomic ssRNA 6- Which is exported to cytoplasm 7- In cytoplasm, host-cell ribosomes catalyse synthesis of virus precursor proteins 8- Which are cleaved into viral proteins by viral proteases 9- HIV ssRNA and proteins assemble beneath the host-cell plasma membrane 10- Forming virion buds from it 11- Maturation occurs either in the forming buds or after budding from the host cell During maturation, HIV proteases cleave the polyproteins into individual functions HIV proteins
58
what 3 mechanisms cause viral genome variation
mutation recombination gene switching/ reassortment
59
do RNA or DNA viruses mutate faster
RNA
60
do ss or ds mutate faster
ss
61
what is antigenic drift
small mutations within antigenic genes that allow viruses to to evade host immune systems
62
describe gene recombination/ reassortment
2 strains of a virus infect the same host recombination -> exchange of entire genes between two strands reassortment -> exchange of entire segments of a genome between strains - both result in antigenic shift
63
how does influenza A exhibit antigenic drift / shift
8 segments of -ve sense ssRNA - susceptible to insertion, deletion and substidution (drift) able to co-infect multiple species (with B) (shift) zoonotic spread of new chains

Week 6 (6 decks)

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