Viruses Flashcards
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
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Virsues infect all cells and organisms:
6 points
- Bacteria: Bacteriophages
- Archaea: Fuselloviruses
- Amoeba: Mimiviruses
- Plants: Tobacco Mosaic Virus
- Insects: Baculovirus
- Animals: HIV, Hepes, Measels
Are viruses alive?
2 points
- 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)
- But they do contain some key features of organic life: DNA/RNA, lipids and protein
Composition of a virus
- Nucleic acid – encoding all proteins required to build capsid/replicate
- Capsid – protein shell protecting nucleic acid and aiding entry to host
- Lipid envelope – not in all viruses!
Viral genomes
6 points
- Single-stranded DNA/RNA
- Double-stranded DNA/RNA
- Positive/negative sense
- Linear/circular
- Single molecule/segmented
- Tiny 2kbp (2 – 4 proteins) - huge 1Mbp (100’s of proteins)
limited by capsid
adaptations: Polyproteins
Alternative reading frames
Segmented genomes in multiple capsids
Virus capsid structure
7 points
- Capsid: protein shell of a virus
- Single, or multiple proteins
- Icosahedral
simple symmetric 60 subunit capsid
complex quasi-symmetric 180 – many-many - Prolate
Elongated icosahedron - Complex
Antennae
Legs
Injection devices - Helical
Filamentous
Rod-shaped - Enveloped
Viral envelope
- Envelope derived from host cell-membrane
- Contain host proteins and viral glycoproteins
- Evasion of host immune system
- Invasion of host cells
- Sensitive to dessication
Viral lifecycles
5 points
Typical Life cycle:
- Attachment: to host cell receptors (adsorption)
- Entry: into the host cell (fusion, endocytosis, injection)
- Genome uncoating and replication
- Expression: Viral gene expression and protein production
- Release: Virions packaged and released (cell lysis or budding)
Viral defense: Restriction enzymes
2 points
- Endonuclease enzymes found in most species of bacteria/archaea
- Cleave at, or near specific DNA sites
Prevent horizontal gene transfer through degradation of non-self DNA
Degradation of viral DNA
Viral defense: CRISPR
4 points
- ‘Adaptive immune system’ in bacteria and archaea
- enzymes that recognise DNA in viral genomes
- if transcribed Cas Proteins bind to viral DNA and remove it.
- Proto spacer (DNA from virus put in genome) if binding between CRISPR RNA the section is chopped.
Miniviruses
- Giant viruses ~ 1um in size
- dsDNA virus
- Icosahedral capsid with fibers
- Large genome - 1.1 Mbp
Influenza
- Enveloped
- Segmented –RNA virus
- Non-geometric capsid
- Key proteins:
Haemagglutinin
Neuraminadise
Kills >36,000 p.a. in USA
Influenza: Haemagglutinin
3 points
- Facilitates entry of virus into host cells
- Binds sugars on host cell surface
- Changes conformation in host cell to fuse membranes and release virus in host
Influenza: Neuraminidase
4 points
- Facilitates exit from host cell
- Binds sugars on host cell surface and cleaves sialic acid sugars from cell glycoproteins
- Prevents virus sticking to cells
- Exit from host cell requires activity of enzyme
Influenza: vaccine
4 points
- Influenza viruses classified based on Haemagglutinin and Neuraminidase subtypes:
H1N1 – Spanish flu
H5N1 – bird flu
- 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. - Traditional flu vaccine: Trivalent: two type A strains: H1N1, H3N3; and a type B strain.
- Seasonal flu vaccine: produced against projected common strains