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MM- Viruses > Hepatitis C > Flashcards

Hepatitis C Flashcards

1
Q

Hepatitis C baltimore classification?

A

Group IV

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2
Q

Hepatitis C genome?

A

+ssRNA

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3
Q

Hepatitis C infection leads to chronic infection in how many cases?

A

60-80%

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4
Q

Hepatitis C early infection symptoms?

A

No symptoms

Asymptomatic

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5
Q

HCV can be cured by?

A

Anti-viral drugs

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6
Q

Family?

A

Flaviviridae

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7
Q

Genus?

A

Hepacivirus

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8
Q

How many ORFs?

A

A single ORF

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9
Q

1 ORF encodes?

A

A polyprotein

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10
Q

The polyprotein results in how many proteins?

A

10

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11
Q

How are 10 proteins made from the polyprotein?

A

Viral encoded and host cell encoded proteases

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12
Q

The genome is flanked by?

A

5’ and 3’ NTR

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13
Q

HCV genome structure?

A

+ssRNA
1 ORF
Flanked by 5’ and 3’ UTR

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14
Q

5’ UTR includes a?

A

IRES

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15
Q

IRES?

A

Internal Ribosomal Entry Site

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16
Q

Structural proteins encoded?

A

Nucleocapsid C

E1 and E2 glycoproteins

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17
Q

Non-structural proteins encoded?

A

P7, NS2, NS3, NS4A, NS5A, NS5B

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18
Q

NS2/3?

A

Autoprotease

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19
Q

NS3/4A?

A

Autoprotease

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20
Q

NS5A?

A

Responsible for creating the membranous web

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21
Q

NS5B?

A

RNA dependent RNA polymerase

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22
Q

E1 function?

A

Fusion

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23
Q

E2 function?

A

Attachment to the cell

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24
Q

NS2/3 mediates cleavage of?

A

NS2/NS3

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25
Q

NS3/4A mediates cleavage of?

A

NS3/NS4A
NS4A/NS4B
NS4B/NS5A
NS5A/NS5B

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26
Q

NS4A is a?

A

Cofactor of the NS3 protease activity

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27
Q

NS3/4A can also cleave cellular factors included?

A

Adaptor proteins essential for signal transduction

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28
Q

NS3/4A can cleave which adaptors?

A

TRIF and MAVS

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29
Q

TRIF is an adaptor in which signalling pathway?

A

All TRLs apart from TLR3 use the Myd88 signalling adaptor
TLR3 uses TRIF
NS3/4A can cleave TRIF

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30
Q

How does NS3/4A interrupt with TLR3 signalling?

A

Cleaving TRIF

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31
Q

TLR3 signalling leads to?

A

Activation of IRF-3 and NF-kB required for IFN-b production

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32
Q

MAVS is also known as?

A

Cardif

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33
Q

How does NS3/4A interfere with RIG-I/MDA-5 signalling?

A

Cleaving MAVS

MAVS is an adaptor that the RLRs- rig like receptors bind to, in order to drive IRF-3 activation and NF-kB

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34
Q

RIG-I senses?

A

Short dsRNA

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35
Q

MDA-5 senses?

A

Long dsRNA

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36
Q

NS3 can also inhibit TBK1 which causes which effects?

A

TBK1 is essential for phosphorylation and activation of IRF-3 in response to cytosolic DNA (DAMPs…)

37
Q

How does NS3 disrupt TBK1?

A

Directly interferes with the binding of TBK1 to IRF-3 and prevents activation of IRF-3 via phosphorylation

38
Q

NS5B has which function?

A

RdRP

RNA dependent RNA polymerase

39
Q

NS5A has which function?

A

Formation of the membranous web

40
Q

P7 is?

A

An ion channel

41
Q

P7 function?

A

Required for viral assembly and release

42
Q

Why is HCV so genetically diverse?

A

Due to RNA polymerase- no proof-reading ability

43
Q

HCV is a genetically diverse virus that can be classified into how many genotypes

A

7

44
Q

Virion structure?

A

E1 and E2 glycoproteins form the envelope

Inside the envelope there is an icosahedral core

45
Q

E1 mediates?

A

Fusion

46
Q

E2 mediates?

A

Cell attachment

47
Q

The virion of HCV is a?

A

Lipoviroparticle

48
Q

Lipoviroparticles contain?

A

Low density and very low density lipoproteins

49
Q

Replication of HCV occurs in?

A

Liver hepatocytes

50
Q

What determines the tropism of this virus?

A

Presence of miRNA-122 in the hepatocytes determines the tropism of the virus, it is required for viral replication

51
Q

Replication of HCV occurs where?

A

In the cytoplasm

52
Q

What is the first receptor HCV binds to?

A

Low affinity receptor

LDLs- low density lipoprotein receptor

53
Q

What high affinity receptor does HCV then bind to?

A

SR-B1

54
Q

Interaction with SR-B1 causes?

A

Conformational changes in viral envelope glycoprotein E2

55
Q

SR-B1 is what type of receptor?

A

A scavenger receptor

56
Q

Binding to SR-B1 causes?

A

A conformational change in E2 causing it to bind to CD81

57
Q

CD81 along with tight junction proteins such as?

A

Claudin-1 and occludin

58
Q

CA81 along with claudin-1 and occludin (tight junction proteins) complex results in?

A

Triggers HCV to be internalised via receptor mediated endocytosis

59
Q

Low pH within the endosomal compartment triggers?

A

Fusion via glycoprotein E1

60
Q

Overview of entry?

A

Low affinity binding to the low density lipoprotein (LDL) receptor
Binding to SR-B1 which triggers a conformational change in E2 and causes binding to CD81
CD81 complex with tight junction proteins (claudin-1 and occludin) triggers clathrin mediated endocytosis of the virion
Low pH in the endosomal compartment triggers a change in the E1 glycoprotein which mediates fusion
+ssRNA then released into the cytoplasm

61
Q

+ssRNA can be directly?

A

Translated

62
Q

Translation occurs where?

A

ER

Endoplasmic reticulum

63
Q

How is translation initiated?

A

CAP independent manner

64
Q

How does IRES initiate translation?

A

Direct binding of IRES to the 40S subunit of the eukaryotic ribosome

65
Q

miR-122 an miRNA is expressed in high levels where?

A

In the hepatocytes

66
Q

What is the function of miR-122?

A

It binds in two places in the 5’UTR upstream of IRES and stabilises the genome allowing translation to occur

67
Q

What determines the tropism of HCV?

A

miR-122 presence

68
Q

Translation yields?

A

A single protein- polyprotein

69
Q

How is the polyprotein processed?

A

By cellular signal peptidase and signal peptide peptidase

By viral proteins

70
Q

How is the polyprotein processed by viral proteins?

A

NS2/NS3 processed by NS2/NS3= autoprotease

NS3/4A processes: NS3/NS4A, NS4A/NS4B, NS4B/NS5A, NS5A/NS5B…= autoprotease

71
Q

How is the polyprotein processed by cellular proteases?

A

Cleavage of E1, E2, nucleocapsid C and P7 is mediated by signal (peptide) peptidases

72
Q

The proteins that are produced are not free-floating they are?

A

Membrane associated

73
Q

RNA replication takes place in?

A

A membranous web

74
Q

Membranous web is formed by?

A

NS5A

75
Q

Membranous web is mostly composed of?

A

Double membrane vesicles containing HCV non-structural proteins

76
Q

How does replication occur?

A

+ssRNA –> -ssRNA intermediate –> +ssRNA

77
Q

What may be the function of the membranous web?

A

To protect the viral RNA from being detected by the immune system

78
Q

Newly synthesised +ssRNA can be used for?

A
  • Packaging into viral particles
  • In translation to make more proteins
  • As a template for more rounds of replication
79
Q

Why is the mutational rate of HCV very high?

A

NS5B is an RdRP

It has no proofreading ability and is very error prone

80
Q

Assembly and release?

A

Core protein from ER membrane to lipid droplets- cytoplasmic organelles
HCV RNA relocated from the membranous web to lipid droplets where they are encapsulated - viral capsid takes a bit of the lipid droplet with it

81
Q

Why do the HCV particles often differ in size?

A

Due to the lipids incorporated into the virion- LVP= lipoviroparticle

82
Q

HCV subgenomic replicon was created in?

A

1999

83
Q

The HCV subgenomic replicon structure?

A

IRES and 5’UTR of HCV
Neo- neomycin phosphotransferase gene
IRES of EMCV
NS3-NS5

84
Q

What has been removed?

A

C,E1,E2,P7,NS2

85
Q

All of the structural proteins were removed so therefore?

A

No infectious particles can be made

86
Q

How can selection occur?

A

Apply to Huh-7 cells on G418 medium (antibiotic)
The antibiotic will kill any cells not expressing the neomycin phosphotransferase which confers resistance to certain antibiotics

87
Q

Which cells will survive?

A

The cells in which the replicon is self-amplifying

88
Q

Advantages of the system?

A

Non-infectious means it can be worked with at the lowest biosafety levels
Can be used in drug research
Helps us to study replication

MM- Viruses (13 decks)

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