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CBG > CBG20 > Flashcards

CBG20 Flashcards

1
Q

What is a virus?

A

a small non cellular agent largely consisting of nucleic acid with a protein case, requiring a host cell for reproduction.
* generally not considered alive.

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2
Q

Why was a virus originally considered not to be alive?

A 
as it had a capsid, 
no ribosomes, 
no respiration 
no metabolism 
 small size 
 self assembly
= not alive.
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3
Q

Give two examples of viruses which go against the original defintion of ‘alive’

A

Pandora virus has no capsid.

mimivirus viruses larger than bacteria

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4
Q

What are the characterisics of an RNA genome?

A

tend to be smaller *can be bigger than 30Kb
doesnt have proof reading capabilities of dna
consequently higher mutation rate
consequently energy off offspring different to parent
therefore is a quaisispecies. - virus does not exist as a single sequence but as a pool of sequences.
This is why its hard to make vaccine for eg. HIV

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5
Q

What do viruses with small genomes tend to have?

A

overlapping genes
frame shift
code for more than 1 protein.

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6
Q

What is the genome diversity of viruses?

A
  • DNA or RNA
  • ds/ss
  • circular (bacterial) or linear (animal)
  • (+)/(-) sense.
  • segmented/non segmented
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7
Q

What is a (+) sense virus?

A

analagous to mRNA

translated directly

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8
Q

What is a (-) sense virus?

A

needs to become (+) sense before translated which influences the life cycle.

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9
Q

What is a segmented genome?

A

genome on lots of pieces of nucleic acid, each segment usually codes for one protein and found together in a capsid.
* however all segments are not required to be in the same virion for the virus to be infectious.

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10
Q

What are the advantages of a segmented genome for the bacteria?

A

allows for dramatic genetic changes by reassortment of its genome.
Allows it to undergo antigenic shift - viruses can exchange genes upon coinfection

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11
Q

Describe the influenza virus

A

negative sense virus with segmented RNA genome
7/8 segments depending on the virus.
evolve by mutation, recombination and reassortment.

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12
Q

What is a virion?

A

RNA/DNA and capsid
Virion partical simplicity is not a reflection of genomes
- sometimes envelope of lipids that surround protein coat.

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13
Q

When does antigenic shift occur?

give an example

A

When RNA segments are exchanged between viral strains in a secondary host.
eg. avian H3 and human H2
H= Hemagglutin type of envelope.

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14
Q

What kind of genomes do retroviruses have?

A 
RNA
positive sense 
non segmented genomes
enveloped virus
evolve by mutation and recombination
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15
Q

What kind of RNA are most RNA viruses?

Give an exception

A

ss
apart from reovirus
*RNA viruses loop so are double stranded in places.

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16
Q

What kind of DNA are most DNA viruses

Give an exception

A

ds
exceptions are some small viruses (less than 4000bp)
eg. parvovirus

17
Q

What is SV40 an example of?

A

a circular dsDNA virus
= found in monkeys and humans
- cells develop unusual number of vaculoles = potential to cause tumours.

18
Q

What do the simplist virus have?

Give an example?

A

a genome surrounded by a capsid (coat)
eg. TMV
Tobacco mosaic virus - + rna virus, infects plants
mosaic like molting and discolouration in leaves
*first virus ever discoverd
the capsid protects the nucleic acid.

19
Q

How can viruses be viewed?

A

EM

ussually too small for light

20
Q

What happens if RNA of virus is put into a test tube with capsid monomers and shaken?

A

self assembly.

21
Q

What is a zoonotic virus?

A

animal virus that can be transmitted to humans

  • ussually worse for new host.
  • viralence decreases over time
  • new virus = high mortality rates as havent been exposed to it before.
22
Q

What can capsid proteins form?

A

one or more icosahedral conformations

23
Q

What is WNV

A

West Nile Virus
mosquito born zoonotic arbovirus (transmitted by arthopod vector)
virus can be transmitted from virus to bird and back to virus as birds= carriers dont ussually die.
humans are dead end carriers
virus in mammals is ussually not sufficient to be transmited back to mosquito.

24
Q

Describe the mimivirus

A 
related to virus like pox
large
900 genes
genome 1mbp
blurs distinction between cellular and life viruses
25
Q

What are the 4 viral groups that can undergo antigenic shift? (therefore are segmented)

A

Banyaviridae
orthomyxoviridae
arenavirus
reoviridae

26
Q

Describe Bunyavirdae

A 
family
- sense
RNA
enveloped
Arthropods and rodents, sometimes humans and plants
27
Q

Describe orthomyxoviridae

A

family
- sense
ssRNA
eg. influenza

28
Q

Describe arenavirus

A

genus
ambisense neg and pos
grainy particles of stolen ribosomes
rodents humans genus

29
Q

Describe Reoviridae

A 
family
dsRNA
non enveloped
replication in cytoplasm and DNA
respiratory tract infections

CBG (19 decks)

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