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Microbiology for Dentists > 2. Viruses and Prions > Flashcards

2. Viruses and Prions Flashcards

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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?

A

used directly as mRNA

18
Q

Viruses are small. What’s their size range?

A

20-200nm

19
Q

Why can viruses not replicate themselves?

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?

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 …

A

beta sheets
amyloid fibrils

22
Q

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

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

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

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

Dental tissue is low/high risk for prion transmission

A

low

25
Q

How do dentistry protocols avoid prion transmission?

A
  • difficult to destroy with autoclaving and no reliable assay
  • strict regulations on decontamination procedures and designation of single use instruments
26
Q

Define ‘virus’

A
  • small, acellular, infectious agents
  • evolved to transfer nucleic acids from one cell to another
27
Q

How do viruses replicate?

A
  • utilise chemical and structural components of cells they infect
  • they’re obligate intracellular parasites
28
Q

What kind of microscopy is needed to see viruses?

A

electron

29
Q

What’s the difference between virus and virion?

A
  • viruses have an intracellular and extracellular state
  • extra is virion
  • intra is virus
30
Q

Structure of a virion

A
  • 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
Q

2 features that distinguish viruses

A
  • nature of nucleic acid
  • virion shape
32
Q

Viral genomes encode what kind of protein?

A
  • viral structural proteins
  • proteins that interact with the host for example proteases, DNA/RNA polymerase, reverse transcriptase, immune system inhibitors
33
Q

Viral genomes can have RNA or DNA, both of which can be … or … stranded and the RNA can be … or …

A
  • single or double
  • positive or negative sense
34
Q

3 ways viral mRNA can be synthesised

A
  • 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
Q

How to synthesise mRNA from negative sense RNA virus?

A

synthesis of RNA complementary to viral RNA

36
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
37
Q

How are polyhedral virions formed?

A
  • capsid is roughly spherical (shape is like a geodesic dome)
  • capsomers are pentamers or hexamers
  • most commonly forms an icosahedron with 20 sides
38
Q

Advantage of polyhedral virion?

A
  • efficient at enclosing space and making a robust structure just from one single repeating protein
39
Q

What shape is T4 bacteriophage?

A

complex

40
Q

What shape is poliovirus?

A

polyhedral

41
Q

How does HIV replicate?

A
  • 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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