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Viruses Flashcards

1
Q

Appreciate the defining features of a virus

Illustrate the basic structure of a virus

Describe some common examples of microbial, human and animal viruses

Compare viruses with viriods and prions, as examples of non-viral infective agents

A

…

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2
Q

Virsues infect all cells and organisms:

6 points

A
  1. Bacteria: Bacteriophages
  2. Archaea: Fuselloviruses
  3. Amoeba: Mimiviruses
  4. Plants: Tobacco Mosaic Virus
  5. Insects: Baculovirus
  6. Animals: HIV, Hepes, Measels
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3
Q

Are viruses alive?

2 points

A
  1. If life is considered to be able to “respond to stimuli, grow and reproduce, metabolize and make energy /ATP”

…then viruses should be considered as non-living

Viruses are acellular, do not grow, do not divide

They are inert: cannot make energy, perform metabolic processes, or respond to stimuli

And they ALWAYS need a host cell to replicate (= obligately intracellular)

  1. But they do contain some key features of organic life: DNA/RNA, lipids and protein
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4
Q

Composition of a virus

A
  1. Nucleic acid – encoding all proteins required to build capsid/replicate
  2. Capsid – protein shell protecting nucleic acid and aiding entry to host
  3. Lipid envelope – not in all viruses!
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5
Q

Viral genomes

6 points

A
  1. Single-stranded DNA/RNA
  2. Double-stranded DNA/RNA
  3. Positive/negative sense
  4. Linear/circular
  5. Single molecule/segmented
  6. Tiny 2kbp (2 – 4 proteins) - huge 1Mbp (100’s of proteins)

limited by capsid

adaptations: Polyproteins
Alternative reading frames
Segmented genomes in multiple capsids

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6
Q

Virus capsid structure

7 points

A
  1. Capsid: protein shell of a virus
  2. Single, or multiple proteins
  3. Icosahedral
    simple symmetric 60 subunit capsid
    complex quasi-symmetric 180 – many-many
  4. Prolate
    Elongated icosahedron
  5. Complex
    Antennae
    Legs
    Injection devices
  6. Helical
    Filamentous
    Rod-shaped
  7. Enveloped
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7
Q

Viral envelope

A
  1. Envelope derived from host cell-membrane
  2. Contain host proteins and viral glycoproteins
  3. Evasion of host immune system
  4. Invasion of host cells
  5. Sensitive to dessication
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8
Q

Viral lifecycles

5 points

A

Typical Life cycle:

  1. Attachment: to host cell receptors (adsorption)
  2. Entry: into the host cell (fusion, endocytosis, injection)
  3. Genome uncoating and replication
  4. Expression: Viral gene expression and protein production
  5. Release: Virions packaged and released (cell lysis or budding)
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9
Q

Viral defense: Restriction enzymes

2 points

A
  1. Endonuclease enzymes found in most species of bacteria/archaea
  2. Cleave at, or near specific DNA sites

Prevent horizontal gene transfer through degradation of non-self DNA

Degradation of viral DNA

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10
Q

Viral defense: CRISPR

4 points

A
  1. ‘Adaptive immune system’ in bacteria and archaea
  2. enzymes that recognise DNA in viral genomes
  3. if transcribed Cas Proteins bind to viral DNA and remove it.
  4. Proto spacer (DNA from virus put in genome) if binding between CRISPR RNA the section is chopped.
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11
Q

Miniviruses

A
  1. Giant viruses ~ 1um in size
  2. dsDNA virus
  3. Icosahedral capsid with fibers
  4. Large genome - 1.1 Mbp
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12
Q

Influenza

A
  1. Enveloped
  2. Segmented –RNA virus
  3. Non-geometric capsid
  4. Key proteins:
    Haemagglutinin
    Neuraminadise
    Kills >36,000 p.a. in USA
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13
Q

Influenza: Haemagglutinin

3 points

A
  1. Facilitates entry of virus into host cells
  2. Binds sugars on host cell surface
  3. Changes conformation in host cell to fuse membranes and release virus in host
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14
Q

Influenza: Neuraminidase

4 points

A
  1. Facilitates exit from host cell
  2. Binds sugars on host cell surface and cleaves sialic acid sugars from cell glycoproteins
  3. Prevents virus sticking to cells
  4. Exit from host cell requires activity of enzyme
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15
Q

Influenza: vaccine

4 points

A
  1. Influenza viruses classified based on Haemagglutinin and Neuraminidase subtypes:

H1N1 – Spanish flu
H5N1 – bird flu

  1. Vaccines produced from viruses grown in hen’s eggs – live attenuated virus
    Egg-free recombinant vaccines: produced from selected H/N subtypes grafted onto insect virus and grown in insect cells.
  2. Traditional flu vaccine: Trivalent: two type A strains: H1N1, H3N3; and a type B strain.
  3. Seasonal flu vaccine: produced against projected common strains
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16
Q

Zika 5 points

A
  1. Flavivirus – similar to bluetongue and dengue
  2. Initially found in a monkey in the Zika forest in Uganda in 1947
  3. Spread by mosquitos
  4. Linked to microcephaly in children born to infected mothers
  5. Surface asparagine residue on capsid is glycosylated
    implicated in uptake by host cells
17
Q

HIV - lifecycle

4 points

A
  1. Lentivirus
  2. Retrovirus – single strand –RNA
  3. Integrates into host genome via dsDNA intermediate
  4. gp120 binds CD4 receptor on macrophages and T-cells
18
Q

reverse transcriptase

3 points

A
  1. Copies retrovirus genome to allow integration into host genome by the integrase enzyme
  2. Bifunctional enzyme:
    RNA dependent DNA polymerase:
    ssRNA -> dsDNA
    Nuclease: digests original RNA strand
  3. Low fidelity – error rate of 1/2000
    Beneficial for virus:
    high mutation rate allows evasion of host immune system and anti-viral drugs
19
Q

Human Papilloma virus

A
  1. Non-enveloped dsDNA virus
  2. Over 170 subtypes
  3. Infects skin/mucosal surfaces
  4. Causes warts
  5. Linked to cervical/anal/throat cancers
  6. Vaccination highly effective –
    100 % effective
    50 % reduced incidence of cervical cancer
20
Q

Ebola

3 points

A
  1. RNA genome
  2. U-shaped filamentous virus
    Transmitted by fruit bats to humans/monkeys - Zoonotic
  3. Causes haemorrhagic fever
    Infects many cell types, particularly monocytes and endothelial cells

Large levels of inflammatory cytokines produced by infected cells

Affects clotting cascade – leads to heamorrhage

21
Q

Baculovirus

6 points

A
  1. Insect viruses
  2. Infect caterpillars – usually narrow host range
  3. Circular dsDNA genome
  4. Capsid
  5. Envelope
  6. Useful in biotech
22
Q

Feline distemper

4 points

A
  1. Feline panleukopenia
  2. Causes gastroenteritis in felines
  3. Kills kittens
  4. ssDNA viruses
23
Q

Plant viruses

A

Gemini viruses:
1. Circular ssDNA genomes

  1. Fused capsids
  2. Sometimes segmented genomes: multiple viruses need to infect for lifecycle
  3. Major crop pests – infect tomatoes, beans, cotton
24
Q

Anti-viral drugs

3 points

A
  1. HIV protease inhibitors:
    Bind to protease and prevent cleavage of polyprotein
  2. Nucleoside analogues: Acyclovir
  3. Guanosine nucleoside analogue: inhibits viral polymerases
25
Q

Non-viral infectious agents
Prions
3 points

A
  1. Protein infectious agents
  2. Cause BSE, vCJD, scrapie
  3. Normal protein PrP found in brain tissue, can mis-fold and aggregate and act as template for more PrP
26
Q

Non-viral infectious agents
Viriods
3 points

A
  1. Circular ssRNA
  2. Infect plants
  3. Major economic impact
  4. No protein!
  5. Spread by leaf/leaf contact and aphids
  6. Proposed to act through RNA silencing
27
Q

basic virus structure

Microbiology (13 decks)

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