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Microbiology for Dentists > 2. Viruses and Prions > Flashcards

2. Viruses and Prions Flashcards

(41 cards)

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1
Q

How do prions spread?

A
  • from cell to cell between individuals
  • via contaminated food, hormone treatments, blood and surgical instruments
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2
Q

What kind of disease do prions cause?

A

neurodegenerative
- transmissible spongiform encephalopathies

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3
Q

How do normal proteins become infectious prions?

A
  • protein undergoes rare conformational change to give abnormally folded prion form
  • this abnormal form causes conversion of normal proteins in the host’s brain into misfolded prion form
  • prions aggregate into amyloid fibrils (which disrupt brain cell function) causing neurodegenerative disorder
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4
Q

Why are viruses acellular?

A
  • no cytosol
  • no cytoplasmic membrane
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5
Q

Give some diseases caused by viruses

A
  • common cold
  • warts
  • chickenpox
  • polio
  • rubella
  • smallpox
  • herpes
  • mumps
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6
Q

Capsids are made of what?

A
  • repeating protein subunits or capsomers
  • a capsomer is composed of a single repeating protein to save on gene space
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7
Q

Togavirus, HIV and SARS-CoV-2 are what shape?

A

enveloped

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8
Q

2 features that can distinguish viruses

A
  • nature of nucleic acid
  • virion shape
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9
Q

Irrespective of the nature of viral nucleic acid, what must happen?

A
  • must be converted to mRNA
  • to allow synthesis of viral proteins
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10
Q

5 stages of viral replication

A
  • attachment of virion to host cell
  • entry of viral nucleic acid into host cell
  • synthesis of viral nucleic acid and proteins
  • assembly of new viruses with host cell
  • release of new virions from host cell
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11
Q

Why does no immune response occur in Creutzfeldt-jakob disease?

A
  • caused by prions
  • the misfolded protein is the human’s own protein so won’t produce an immune response
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12
Q

4 main virion shapes seen in EM

A
  • helical
  • polyhedral
  • complex
  • enveloped
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13
Q

Shape of virus is determined by what?

A

capsid

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14
Q

3 types of Creutzfeldt-Jakob disease

A
  • spontaneous (sporadic)
  • inherited (familial)
  • acquired (variant)
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15
Q

Where does viral proteinsynthesis occur?

A

on host cell ribosomes

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16
Q

Explain lytic replication

A
  • replication cycle usually results in lysis and further death of host cell
  • lysis allows newly synthesised virions to be released
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17
Q

How to synthesise mRNA from positive sense RNA virus?

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A

used directly as mRNA

18
Q

Viruses are small. What’s their size range?

19
Q

Why can viruses not replicate themselves?

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A
  • don’t possess genes encoding enzymes required for nucleic acid replication
  • don’t produce ribosomes for protein synthesis
20
Q

How do helical virions form?

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A
  • capsomers bond together in spiral fashion
  • form a tube around nucleic acid
  • results in rod-shaped or filamentous virions
21
Q

Stacking of … allows misfolded proteins to aggregate into …

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A

beta sheets
amyloid fibrils

22
Q

Which is the most common prion disease?
What frequency has it?

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A
  • sporadic CJD
  • 1-2 per million
23
Q

Misfolded proteins can contribute to non-infective tissue degenerative disorders e.g …

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A
  • Alzheimers
  • Parkinsons
  • Hungtindon’s
  • atherosclerosis
  • type 2 diabetes
24
Q

Dental tissue is low/high risk for prion transmission

25
How do dentistry protocols avoid prion transmission?
- difficult to destroy with autoclaving and no reliable assay - strict regulations on decontamination procedures and designation of single use instruments
26
Define 'virus'
- small, acellular, infectious agents - evolved to transfer nucleic acids from one cell to another
27
How do viruses replicate?
- utilise chemical and structural components of cells they infect - they're obligate intracellular parasites
28
What kind of microscopy is needed to see viruses?
electron
29
What's the difference between virus and virion?
- viruses have an intracellular and extracellular state - extra is virion - intra is virus
30
Structure of a virion
- protein coat surrounding the nucleic acid is called a capsid - coat and nucleic acid is referred to as nucleocapsid - some have an additional phospholipid membrane called envelope outside nucleocapsid
31
2 features that distinguish viruses
- nature of nucleic acid - virion shape
32
Viral genomes encode what kind of protein?
- viral structural proteins - proteins that interact with the host for example proteases, DNA/RNA polymerase, reverse transcriptase, immune system inhibitors
33
Viral genomes can have RNA or DNA, both of which can be ... or ... stranded and the RNA can be ... or ...
- single or double - positive or negative sense
34
3 ways viral mRNA can be synthesised
- transcribed from viral DNA (DNA virus) - synthesis of RNA complementary to viral DNA (negative sense RNA virus) - used directly as mRNA (positive sense RNA)
35
How to synthesise mRNA from negative sense RNA virus?
synthesis of RNA complementary to viral RNA
36
Capsids are made of what?
- repeating protein subunits or capsomers - a capsomer is composed of a single repeating protein to save on gene
37
How are polyhedral virions formed?
- capsid is roughly spherical (shape is like a geodesic dome) - capsomers are pentamers or hexamers - most commonly forms an icosahedron with 20 sides
38
Advantage of polyhedral virion?
- efficient at enclosing space and making a robust structure just from one single repeating protein
39
What shape is T4 bacteriophage?
complex
40
What shape is poliovirus?
polyhedral
41
How does HIV replicate?
- fusion of HIV to host cell surface - HIV RNA, reverse transcriptase, integrase and other proteins enters host cell - viral DNA formed by reverse transcriptase - viral DNA transported across nucleus and integrates into host DNA - new viral RNA is used as genomic RNA and makes viral proteins - new viral RNA and proteins move to cell surface and new immature HIV forms - virus is released and viral protease cleaves new polyprotein to create mature infectious virus

Microbiology for Dentists (37 decks)

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