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Y3 Medical Micro > L3 Virology > Flashcards

L3 Virology Flashcards

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USMLE® Step 1 flashcards
1
Q

what are viruses

A

obligate intracellular parasites

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2
Q

what is the structure of a virus

A

nucleic acid surrounds by protein capsid (some also have lipid membrane - from host cell, acquire lipid membrane through one of the membranes in the eukaryotes e.g. cytoplasmic membrane)

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3
Q

how do viruses enter cells

A

via interaction with specific cell receptors (lock and key) = TROPISM (which cells, tissues, organisms can the virus infect)

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4
Q

how do viruses replicate when in host

A

host cell machinery is hijacked resulting in synthesis of new virus

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5
Q

how are viruses released

A

by budding (enveloped viruses) or by cell lysis or via the secretory pathway

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6
Q

what viruses dont result in a disease

A

orphan viruses

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7
Q

what can viruses infect

A

bacteria
plants
animals
humans

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8
Q

what is transmission electron microscopy

A

electrons pass through thin fixed specimen
electrons are blocked by it
electrons transmitted through specimen according to electron density

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9
Q

what is scanning electron microscopy

A

specimen often immobilised and fixed on grid
electron interact with surface and back scattered also make x rays- both detected
gives surface topography

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10
Q

what is scanning EM good for

A

viruses without lipid membrane (rigid structure)

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11
Q

what is cryo-electron microscopy

A

specimen unfixed
immobilised by freezing to near zero temp
preserves native structural features
cyro-electron tomography uses 2D images to build 3D pic

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12
Q

what is the effect of reducing the temp in cryo EM

A

reduce energy of virus so stop vibrating can see the virus

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13
Q

what is a virion

A

virus particle

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14
Q

what nucleic acid does a virus carry

A

RNA or DNA

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15
Q

what nucleic acids do most viruses have

A

RNA

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16
Q

what surrounds the virus

A

nucleic acid plus protein = nucleocapsid

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17
Q

how are capsids arranged

A

in symmetrical patterns

most energetically favourable state

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18
Q

what is the most favourable state for HIV

A

helical nucleocapsid with icosahedral core

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19
Q

where do viruses get the lipid envelope

A

host cell membrane

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20
Q

how viruses attach to cells

A

some of the virus proteins are involved in cell attachment and entry, (usually on the surface to allow virus to stick to cell they want to infect)

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21
Q

what sort of enzymatic functions do viruses have

A

copying viral genome (polymerases)
trimming viral proteins (proteases)
other modifying enzymes

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22
Q

what microscopy can see most viruses

A

electron

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23
Q

what is the hierarchical classification system

A

grouped according to shared properties

  • nucleic acid
  • capsid symmetry
  • presence/absence of envelope
  • size
  • ss/ds
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24
Q

what is the family suffix

A

-viridae

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25
Q

what is the genera suffix

A

-virus

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26
Q

ICVT hierarchy of viral taxa

A

(order) > family > (sub-family) > genus > species

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27
Q

what is baltimore classification

A

system based on replication strategy
dictated by RNA or DNA genomes they contain
7 arbitrary groups

28
Q

what is group 1

A

dsDNA

29
Q

what do group 1 viruses do

A

dsDNA can replicate in nucleus (hijack your cells) or

cytoplasm and make their own enzymes for nucleic acid replication

30
Q

which group 1 viruses replicate in nucleus

A

adenovirus uses cellular proteins

31
Q

which group 1 viruses make own enzymes for nucleic acid replication

A

poxvirus

32
Q

what are the group 2 viruses

A

ssDNA

33
Q

what do group 2 viruses do

A

ssDNA replicate in nucleus

involve formation of (-) sense strand, serves as template for (+)strand RNA and DNA synthesis

34
Q

what are the group 3 viruses

A

dsRNA

35
Q

what are group 3 viruses like

A

dsRNA have segmented (usually each segment encodes one protein - monocistronic) or non-segmented linear genomes

36
Q

how do dsRNA viruses transcribe

A

most viruses with a segmented genome, each segment is transcribed separately to produce monocistronic mRNAs

37
Q

what are the group 4 viruses

A

(+) sense RNA viruses (enveloped)

+) sense RNA viruses (non-enveloped

38
Q

what do group 4 (+) sense RNA viruses (enveloped) do

A

mRNA naked RNA infectious - make new proteins which make new virus
translation = formation of polyprotein product

39
Q

what are the group 4 (+) sense RNA viruses (non-enveloped)

A
  • astrovirus
  • calicivirus
  • hepatitis a virus Picornaviridae
40
Q

why are group 4 viruses best to see under microscope

A

as non-enveloped

41
Q

what are the group 5 viruses

A

(-) sense RNA viruses (non-segmented enveloped)

-) sense RNA viruses (segmented enveloped

42
Q

what do group 5 (-) sense RNA viruses (non-segmented enveloped) have

A

have a virion particle RNA directed RNA polymerase

43
Q

what is the first stage of group 5 (-) sense RNA non segmented enveloped viruses

A

transcription by viral RdRp to produce monocistronic mRNAs

44
Q

why do group 5(-) sense RNA viruses (non-segmented enveloped) have their own RNA polymerase

A

need own RNA polymerase to make it positive strand as they are negative strand

45
Q

what are group 6 viruses

A

RNA reverse transcribing viruses

46
Q

example of group 6 viruses

A

retroviridae: HTLV-1, HIV

47
Q

what is the genome of group 6 viruses

A

(+)sense but unique among viruses in that it is DIPLOID (two copies of (+) strand RNA)
serve as a template for reverse transcription to yield dsDNA

48
Q

what are the group 7 viruses

A

DNA reverse transcribing viruses

49
Q

example of group 7 viruses

A

hepadnaviridae - hepatitis B

50
Q

what do group 7 viruses need to make dsDNA

A

rely on reverse transcription from an RNA intermediate transcript to form partial dsDNA copy

51
Q

what happens first when group 7virus infects cell

A

repair of the gapped genome, followed by transcription

52
Q

what is the replication process of a virus

A 
viral entry: receptor, tropism
uncoating
transcription and translation 
- viral proteins
> structural, enzymatic and regulatory 
- viral genome production 
virus assembly
virus release
53
Q

what changes to endosome as passes through cell

A

pH gets more acidic can hijack the cell

54
Q

what is needed for RNA virus replication

A

RNA dependent RNAse

55
Q

what do reverse transcribing viruses have/make - nucleic acids

A

RNA and DNA

56
Q

where can nucleocapsid assembly occur

A

nucleus or cytoplasm

57
Q

where do envelope viruses bud

A

cell membrane

sometimes golgi/ER

58
Q

where do non-envelope viruses mature

A

golgi/cytoplasm

59
Q

where are mature non-envelope viruses transported

A

secretary vesicles

60
Q

what happens when a (+) sense RNA viruses (non-enveloped) is introduced into cytoplasm

A

RNA in cytoplasm = virus

61
Q

what are group 5(-) sense RNA viruses (non-segmented enveloped)

A
  • paramyxovirus (MMR)

- ebolavirus (filoviridae)

62
Q

where is the reverse transcription needed for group 7 DNA

A

inside maturing virus particle

63
Q

what are the group 4 (+) sense RNA (enveloped) viruses

A

coronavirus

togavirus

64
Q

what is the group 2 viruses

A

paroviridae

65
Q

what is the segmented dsRNA virus example

A

reoviridae

66
Q

what the the non-segmented dsRNA virus example

A

cystoviridae

67
Q

what are the group 5 (-) sense RNA (segmented enveloped) viruses

A
  • arenaviridae
  • bunyaviridae
  • orthomyxoviridae

Y3 Medical Micro (16 decks)

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