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Virology > Simple +ssRNA viruses: Picornaviridae and Flaviviridae > Flashcards

Simple +ssRNA viruses: Picornaviridae and Flaviviridae Flashcards

(54 cards)

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1
Q

What type of genome do simple +ssRNA viruses have?

A

monopartite

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2
Q

What are two examples of simple +ssRNA viruses

A

Picornaviridae

Flaviviridae

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3
Q

What viral family does poliovirus belong to

A

Picornaviridae

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4
Q

What viral family does Rhinoviruses belong to

A

Picornaviridae

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5
Q

What viral family does Enteroviruses belong to

A

Picornaviridae

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6
Q

What viral family does Hepatitis A virus belong to

A

Picornaviridae

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7
Q

What are medically important human viruses that are in the Picornaviridae family

A

Poliovirus
Rhinovirus
Enteroviruses
Hepatitis A virus

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8
Q

What are morphological features of Picornaviridae viruses

A

pico means small so they are small RNA viruses

7500bp genome

non-enveloped

icosahedral capsid

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9
Q

During gene expression do Picornaviruses have a 3’ poly A tail or a 5’ cap or both

A

Picornaviruses have a 3’ poly A tail

they do not have a 5’ cap, a viral protein VPg is attached to the 5’ end instead

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10
Q

Without a 5’ cap how do picornavirus viral proteins get translated

A

use an internal ribosomal entry site IRES

they have a viral protein VPg attached to the 5’ end as well

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11
Q

What is the IRES and how is it used in Picornaviruses

A

Internal Ribosome Entry Site

It is located in this order 5’ of start codon, IRES, 3’ Vp6 (end of genome)

adopts a specific 3D conformation that allows it to bind to ribosomes and direct translation

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12
Q

What is inhibited during picornavirus gene expression, what does this lead to

A

cap-dependent translation is inhibited of the host translation

target eIF4GI and 46II for degradation, these are necessary host translation factors

the degradation of the above host factors leads to only the translation of viral proteins so only viral proteins are made

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13
Q

How are the genes of picornaviruses expressed

A
  1. genome is translated as one polyprotein
  2. the polyprotein is then cleaved at specific sites by viral proteases, protease specific for picornaviruses is 3C
  3. the rate of cleavage is distinct at each site dictating how much of each protein is made
  4. structural proteins are made at the 5’ end and non-structural proteins are made at the 3’ end
  5. release non-structural proteins first and release structural proteins after
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14
Q

What end are structural proteins made in the picornaviruses

A

5’ end form structural proteins and these are released after the non-structural proteins

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15
Q

What end are non-structural proteins made in the picornaviruses

A

3’ end form the non-structural proteins and these are released first before the structural proteins are

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16
Q

What cleaves a polyprotein

A

proteases

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17
Q

Where does picornavirus replication occur

A

occurs on double membrane vesicles that are derived from the ER or autophagic membranes

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18
Q

Where are the double membrane vesicles where picornavirus replication occurs derived from

A

from the ER or autophagic membranes

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19
Q

What has to happen in picornaviruses before replication can begin

A

replication first requires translation of viral proteins

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20
Q

Are polymerase and other replicase proteins present in the virion of picornaviruses

A

no

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21
Q

What happens after translation of viral proteins in picornaviruses

A

the virus must make - RNA

dsRNA intermediate

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22
Q

Where does initiation occur in picornaviruses

Study These Flashcards
A

initiation must occur at the 3’ end of the genome

23
Q

How is the genome held in picornavirus replication

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A

genome is held in a circular form

24
Q

What is the process of picornavirus genome replication

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A
  1. genome is held in a circular form
  2. Host Poly A and Poly C binding proteins are brought together by 3CD protein
  3. 3CD is the precursor for the polymerase, 3D is the polymerase
  4. once it is ready to leave it is activated by proteolytic cleavage and replicates RNA from the 3’ end of the template
25
What is the role of Host Poly A and Poly C, viral 3DC and 3D in picornaviruses
picornavirus replication genome is held in a circular form Host Poly A and Poly C are binding proteins that are brought together by 3CD protein 3CD is the precursor of the polymerase 3D is the polymerase once its ready to go, it is activated by the proteolytic cleavage and replicates RNA from the 3' end of the template
26
In picornavirus replication, once RNA synthesis initially begins what happens
Once RNA synthesis begins, the polymerase proceeds along the entire length of the template RNA 3' end of the template will become available for further replication before the first complexes are finished up to five complexes can be formed on a genome this is called the replicative intermediate or RI dsRNA is likely unwound by the viral helicase (maybe 2C protein)
27
What is the replicative intermediate RI in picornaviruses
when the 3' end of the template will become available for further replication before the first complexes are finished up to five complexes can be formed on a genome
28
What is dsRNA likely unwound by in picornaviruses
viral helicase maybe 2C
29
How many complexes can be formed on a picornavirus genome
up to 5 replicative intermediates?
30
In picornavirus after -RNA synthesis what occurs
+ RNA synthesis occurs in much the same way
31
How does +RNA synthesis occur in picornaviruses
much the same way of -RNA synthesis production of these RNA is asymmetric much more + RNA is made than -RNA only +RNA is release from replication complexes will be packaged into virions
32
In picornaviruses is more +RNA or -RNA made
more +RNA is formed
33
What type of RNA packaged into virions of the picornavirus
only +RNA is released from replication complexes and packaged into virions
34
How does the picornavirus know which one to package
packaging signals is only on the +RNA strand and not on the -RNA strand, therefore only +RNA is packaged into virions
35
What are medically relevant Flaviviridae
arboviruses West Nile Virus Zika Virus Dengue Virus along with many others
36
What are morphological features of the Flaviviridae family
+ssRNA enveloped virion is spherical 50um in diameter
37
What are the similarities between Flaviviridae and Picornaviridae gene expression, two main points
gene expression is very similar genome is translated into a single polyprotein and cleaved by viral proteases structural proteins at 5' and nonstructural proteins at 3' end
38
What are the differences between Flaviviridae and Picornaviridae gene expression
Flaviviridae have have a 5' cap do not have a poly A tail sfRNA: subgenomic flavirus RNA
39
What are sfRNA and what viral family are they located in
subgenomic flavirus RNA found in Flaviviridae
40
Is sfRNA transcribed
it is not transcribed
41
How is sfRNA formed
it is NOT transcribed it is the incomplete digestion of gRNA by cellular exoribonucleases
42
What is the function of sfRNA
has important functions countering IFN, RNAi, RNA decay and transmission
43
Where does Flavivirus replication occur
viral replication occurs on the ER-derived membranes that form viral factories these are single membranes
44
What are the four viral proteins that are NOT transmembrane proteins in Flaviviridae
polymerase NS5 protease NS3 capsid protein NS1
45
What is the role of NS5, NS3, capsid protein and NS1 in Flaviviridae and where are they located
not transmembrane NS5: polymerase, needs to move so it cannot be embedded in the membrane NS3: protease, has to cleave so it cannot be embedded in the membrane capsid protein: capsid cannot be embedded in the membrane NS1
46
Does it matter which side of the membrane the polymerase is on in Flaviviridae replication
yes, the membrane is not a straight line, its in some type of vesicle form, the RNA has to be exposed for translation at some point so the non-transmembrane protein have to be on the outside of the membrane and not transmembrane to help in this process
47
The genome of Flaviviridae and Picornaviridae both encode for what?
a polyprotein that is cleaved by viral proteases
48
When are replicative intermediates formed
during replication where multiple initiations occur, up to 5 complexes can be formed in the Picornaviridae
49
What does it mean by RNA replication is asymmetric
means that much more +RNA is produced that -RNA
50
Does the IRES allow for transcription, replication, or translation
translation
51
How do Picornaviruses prevent host translation
cap-dependent translation is inhibited —- host translation has 5’ cap the virus targets the eIF4G and 46II for degradation (these are necessary host translational factors) host translation is prevented so only viral proteins are made
52
How is the picornavirus polymerase activated
activated by proteolytic cleavage and replicates RNA from the 3' end of the template
53
What does it mean if RNA virus replication is asymmetric
if RNA virus replication is asymmetric then much more + or - sense RNA is made over the other if there was equal amounts then they would form together making dsRNA that would be recognized by the host in picornavirus replication more + RNA is made than - RNA
54
Why do PV replicate asymmetrically
if RNA virus replication is asymmetric then much more + or - sense RNA is made over the other if there was equal amounts then they would form together making dsRNA that would be recognized by the host in picornavirus replication more + RNA is made than - RNA

Virology (6 decks)

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