Lec 11-Structure Flashcards
What is a virus particle?
Molecular structures that package virus genomes in infected cells and transmits them to new cells —not necessarily infectious. The box where genome is put
What is a virion?
A complete, infectious, virus particle
Viral particle relation to virion?
A lot needs to go right to make a viral particle infectious, but if these things do go right it is a virion
Virion must be: (5 things)
- Correctly assembled
- Escape the cell in which they are made
- Withstand the extracellular environment
- Attach to and enter another host cell
- Uncoat and release the viral genome
Virus diversity
Diff viruses face diff challenges in their host cells and extracellular environments—eg. Compare bacteriophage T4 (infects E. coli in gut) to HSV1 (infects oral epithelial cells). They are 2 very diff viruses due to the difference in their hosts and environments
Capsids:
A rigid, symmetrical container for viral genomes
What do capsids protect nucleic acid genome from?
Physical damage—shearing by mechanical force
Chemical damage—UV radiation from sun leading to chem modification
Enzymatic damage—nucleases derived from dead/leaky cells or deliberately secreted by vertebrates as defence against infection
Capsomers
Protein subunits in a virus capsid that are multiply redundant (many copies per particle)
Metastability of viral capsids
They are metastable. Strong enough to withstand environment and protect genome, but its shell can be primed and disassemble during virus entry (uncoating)
4 virus morphologies and examples:
- Helical: rod shaped (eg. Tobacco mosaic virus)
- Icosahedral: 20 sided (eg. Polio, adenovirus, hep A)
- Enveloped: guts of capsid protected by lipid layer derived from PM of hosts (eg. Covid, HIV)
- Complex: combo of the other 3 (eg. bacteriophage: icosahedral head, helical tail)
Helical capsids
Simplest type, composed of 1 type of capsomer stacked around a central axis forming helical structure. Center of helix contains viral genome (usually ssRNA)
How do capsomers bind to viral genome?
Electrostatic interactions aid assembly by guiding RNA into protein subunits:
- RNA backbone has neg charge (phosphodiester bonds), each subunit of shell has pos charged AAs facing inside of tube
Does genome sequence impact capsomer binding?
Scrambling genome sequence doesnt matter bc backbone will still be neg charged (not sequence specific), gives virus a chance to change
What governs length and diameter of helix?
Width of coil of RNA
Icosahedron structure:
20 faces, 30 edges, 12 vertices
Polio VS adenovirus VS hep A EM photos
Polio has a bunch of icosahedrons rly close together, adeno has projections off icosahedrons to attach to eachother, hep A is even further apart
What are hep A icosahedrons built from?
4 types of proteins:
- VP1, 2 and 3 are surface
- VP4 is more interior
Advantages of icosahedral:
- Strong
- Resistant to shear forces—i.e. if put in fast moving fluid they can resist the movement
- Tight packaging of genome—maximal volume:maximal surface area ratio
- Genetic economy—can be built from a few repeating subunits, viruses are small and each one needs a gene; ideally the genome would be small so it can fit into small packages
What kinds of viruses have icosahedral capsids?
- Eg. Human virus (common cold), pig virus, plant virus, insect virus, bacteriophages can all be hosts that can be infected by viruses with icosahedral shell
- Any genome type introduced at start of lecture can fit into a box like this —eg. ssRNA, ssDNA, etc
Enteric viruses
- Many viruses with icosahedral capsids are enteric viruses
- Enteric virus: affect GI tract
- GI tract: digestive enzymes, low pH, harsh environment for viruses
- Icosahedral structure is advantageous bc of how strong they are, can handle hostile environment
Decontamination of surfaces with enteric viruses:
- We would rather use bleach (oxidizer) than detergent (protein denaturer)
- We will fully inactivate a virus with bleach
- Bleach does need time in order to work
What do enveloped viruses do?
Cover themselves in an outer layer of host cell lipid membrane called the envelope, they steal a chunk of these membranes on their way out of the cell
What does the envelope on viruses contain?
Membrane spanning viral glycoproteins that play important roles in infection
Viral glycoproteins are modified with …
Host sugars added in the ER and golgi
