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MII2 > Viruses > Flashcards

Viruses Flashcards

1
Q

Define a virus.

A

a nucleoprotein complex that infects cells and uses the cells’ metabolic processes to replicate
no metabolic activity outside the host cell
highly species specific

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2
Q

What is the difference between naked and enveloped viruses?

A

enveloped viruses have an envelope in addition to the capsid, naked viruses do not
this envelope facilitates entry into host cells but since this envelope is derived from host membrane that means it is more susceptible to environmental conditions

naked viruses rely on direct cell to cell contact for transmission

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3
Q

What is the difference between single stranded positive sense and single stranded negative sense RNA?

A

+sense = coding strand, acts like mRNA and can be translated directly
-sense = template strand, must be transcribed into mRNA

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4
Q

What is the simplified process of the virus lifecycle?

A
  1. binding to cell surface receptors
  2. entry
  3. uncoating
  4. replication
  5. transcription
  6. translation
  7. virion assembly
  8. release
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5
Q

What receptors does HIV bind to?

A

CD4+
coreceptors are CCR5 (macrophage) and CXCR4 (T cells), both transmembrane proteins

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6
Q

What receptors does influenza recognise and bind to?

A

sialic acid
Avian and Human influenza prefer different sialic acid isomers -> species barrier

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7
Q

What mechanisms does a virus use to enter a host cell?

A
  1. endocytosis
  2. fusion of virus envelope w cell membrane
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8
Q

Once it has entered the host cell how is the virus uncoated?

A

cell enzymes (lysosomes) strip off virus protein coat
virion can no longer be detected, ‘eclipse period’

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9
Q

Where does virion assembly take place?

A

nucleus, cytoplasm or at plasma membrane (most common w enveloped viruses)

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10
Q

How are virions released from the cell?

A

i. sudden rupture of cell (non-envelope viruses)
ii. gradual extrusion (budding) of enveloped viruses through the cell membrane
iii. may occur together w assembly

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11
Q

What are polyproteins and why does poliovirus produce them?

A

polyproteins are v large proteins encoded by entire RNA genome which are proteolytically cleaved at certain sites in the poly proteins

this is because eukaryotic cells do not encode for more than one protein on each RNA

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12
Q

How does influenza produce variation in the proteins it produces?

A

it has a segmented genome, 8 short strands each of which can be alternatively spliced to produce different proteins (i think the mRNA is spliced together?)

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13
Q

How do coronaviruses produce variation in the proteins it produces?

A

they use multiple transcripts, the length of the genome replicated determines the protein made

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14
Q

What are some methods which anti-viral drugs use to inhibit viruses?

A
  • attachment antagonists
  • inhibit uncoating
  • inhibit DNA/RNA synthesis
  • block maturation
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15
Q

What are the routes of transmission viruses can take?

A
  1. horizontal transmission
    - direct contact
    - respiratory
    - etc
  2. vertical transmission
    - mother to fetus
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16
Q

When can transmission of viruses occur?

A
  1. during asymptomatic shedding of virus
  2. during incubation period
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17
Q

Define acute, chronic, and latent infections.

A

acute - a short-lived infection that occurs when a virus rapidly replicates in the host’s cells (days/weeks)

chronic - a long-lasting infection that occurs when a virus persists in the host’s body for an extended period, often for months or years

latent - when a virus infects a host and remains dormant or inactive in the host’s cells for an extended period of time

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18
Q

What is a cytopathic effect?

A

morphological, functional, or structural alterations to cells during viral infection
- translation shut off
- apoptosis
- immortalisation of cell (tumours)

-syncitia formation
-plaques (holes in mono layer of cells caused by necrotic effect of virus)
-inclusion bodies (virus production centre in cytoplasm, eg in rabies)

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19
Q

What is the mechanism of cancer-causing HPVs to disrupt the cell cycle?

A

E6 and E7 genes mediate destruction of the tumour suppression proteins p53 and PRB respectively

20
Q

What are interferons?

A

small molecules produced in response to virus infection
major role in the inhibition of virus infection in cells
does this by inducing an antiviral state in neighbouring cells

21
Q

What is a cytokine storm?

A

feedback loop caused by damage of cell produces more and more cytokines causing an overreaction of the innate system which can have adverse effects

22
Q

Give an example of a PRR that is common during infection of a cell by a virus?

A

detection of nucleic acid in the cytoplasm and endosomes (only there due to virus)

23
Q

What are some immune modulation strategies used by viruses?

A
  1. secreted modulators
    eg cytokine/chemokine mimics and binders
  2. modulators on infected cell surface
    eg mimics/antagonists of immune signalling
  3. stealth/Latency
    eg express few/ no proteins
  4. antigenic hypervariability
    eg HIV, influenza
  5. block adaptive immune response
  6. inhibit complement system
  7. interfere with PRRs
  8. Block interferon and/or inflammatory cytokines
24
Q

Viral capsid properties?

A

Protect Nucleic acids
Aid in transfer to host
Can be polyhedral or helical
Made up of capsomere subunits

25
Q

Glycoprotein spikes?

A

Present on envelope surface
Bind to cell receptors and facilitate entry and release

26
Q

How are viruses categorised?

A

1.Nucleic acid sequence (most important)
2.Nucleic acid type
3.Envelope present?
4.Helical vs icosahedrons symmetry

27
Q

What sense is mRNA?

A

+sense

28
Q

Common method for culturing viruses?

A

Growing them in chicken egg
Different membranes for different viruses

29
Q

Quantifying viruses?

A

Plaque assay
Serial dilutions plated
Areas of clearing on plate represent a single infection event (similar to counting bacterial CFUs)

30
Q

What is Adsorption?

A

Attachment of virus to host cell
Randomly collided with correct receptor
Specific proteins on viral surface interact with target cell membrane receptors
Not all cells carrying this receptor can be productively infected as other factors may need to be present (eg certain TFs)
Some viruses need >1 receptor

31
Q

Tropism?

A

Host range
The limited cell type spectrum that a virus can infect

32
Q

What do most neutralising antibodies target on viruses?

A

Virion attachment proteins

33
Q

Influenza entry and uncoating methods?

A

Enveloped virus
Low pH in endosome - conformation change in virus HA (Haemagglutinin, a fusion protein)
Acts similarly to a SNARE protein (neurotransmitter vesicles) to bring the membranes together and fuse them

34
Q

Poliovirus entry and uncoating strategy?

A

Non-enveloped, naked virus
Taken into endosome
Causes conformational changes to structure proteins
Causes pore to form in endosome membrane
RNA releases through pore into cystoplasm

35
Q

How do nerve infecting cells traverse axon?

A

Energy dependent travel along microtubules
Travel retrograde to reach nucleus
Then travel anterograde to to surface to release - symptoms shown then

36
Q

viral Budding?

A

Virus cell exit strategy
Nucleocapsid interacts w viral glycoproteins on cell membrane to form the envelope around the capsid and budd off the membrane

37
Q

when is HIV infectious?

A

Only after maturation driven by Virion protease

38
Q

What are the Nucleic acid polymerases used by viruses?

A

-DNA dependent DNA polymerase
-DNA dependent RNA polymerase
-RNA dependent RNA polymerase
-RNA dependent DNA polymerase (reverse transcriptase)

Some viruses use the DNA dependent RNA polymerase present in cells

All RNA viruses need to encode RNA dependent RNA polymerase, not present in eukaryotes

39
Q

dsDNA genome?

A

Enter nucleus (except pox), needed host enzymes are there
Make mRNA and more dsDNA from genome

40
Q

ssDNA genome?

A

Needs to convert ss to ds
ds used to make protein
Then converted to ss form for packaging

41
Q

dsRNA genome?

A

Retroviridae
+sense strand used as mRNA to make viral proteins and more dsRNA

42
Q

ssRNA genome?

A

+sense genome can be directly used as mRNA
Also used as template for -sense RNA which is used as a template for more +sense RNA (for protein translation and packaging into new viruses)

-sense genome is converted into +sense rna which is used as mRNA and also as a template for more -sense for packaging

Some +sense use a DNA intermediate which integrates into genome
The dsDNA is used as a template for +sense RNA (used as mRNA and for packaging)

43
Q

How can segmented genomes present evolution opportunities?

A

2 different strains of a segmented genome virus infect same host at same time
Reassortment of segments in new packaged viruses - kinda like independent assortment of chromosomes - gives new segment combinations

Pigs make good mixing pots as can be infected relatively efficiently by some avian, swine and human strains

44
Q

Influenza drug targets?

A

Amatadines block entry and uncoating
Nucleoside analogues block genome replication (targets RNA pol action)

45
Q

Viremia?

A

Detectable levels of virus in blood
Secondary viremia can come after secondary round of replication

46
Q

Summary of Effects of virus on cell?

A

Apoptosis (cell defence)
Host cell protein translation switch off
Transformation (can cause cell immortalisation)

47
Q

Strategies of viruses to have their genes translated?

A

Viral 5’ UTR
Contains IRES, internal ribosome entry site
Acts like 5’ cap

Influenza mRNA cal stealing
Uses cap as primer for its own mRNA
Allows translation of its viral mRNA
Reduced host protein expression

MII2 (13 decks)

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