Section 4 Flashcards
Giant viruses are called:
Nucelocytoplasmic large DNA viruses (NCLDVs)
NCLDVs facts
- 6 families
- large ds DNA geomes
- share sets of “core” genes
NCLDVs #1:
Phycodnaviruses
Phycodnaviruses
viruses that infect algea (best studied eukaryotic viruses)
Phycodnaviruses (PBCV-1) infect:
Chlorella alga symbionts that live in paramecium
Phycodnaviruses (PBCV-1) stands for
paramecium bursary chlorella virus
PBCV-1 structure:
icosahedral with
1- spike at one vertex that attaches to cell
2- fibers sticking out from capsid that also help with its attachment
3- rigid cell wall
Inside PBCV-1 virion at the vertex where the spike is looks different because
it has lower density than rest of the virion due to more packaged protein and less DNA
PBCV-1 attaches to virus at spike and makes a _____ through the algae cell wall then proteins are released into the cells cytoplasm
hole
Phycodnaviruses have been found in ______ and show decline in performance on cognitive tests
brain
Mice that were infected with virus containing algae showed: (3 things)
1- decline in cognitive test performance
2- 1/3 had antibodies against the virus
3- showed changes in genes associated with cognitive function and immunity
algae that have chalk plates on the outside of their cells: __________
viruses that infect this chalk type of algae: _____________
coccolithophores
cocolithoviruses
coccolithophores form:
large blooms in ocean seen from space due to their chalky exterior
when blooms end, lots of cocolithoviruses are found in seawater
cocolithoviruses (ex. EhV-86) encode
proteins that synthesize the sphingolipid ceramide
sphingolipid ceramide from cocolithoviruses are involved in: (2 things)
1- forming lipid rafts in cells membrane to allow virus to exit
2- blocking the cells apoptosis pathway to allow the virus to keep replicating
effect of cocolithovirsues on climate
1- Lysis of these algeal cells releases volatile chemical DMS (dimethyl sulfide) that forms clouds
2- these clouds prevent sunlight to ocean and block phytoplankton growth
NEGATIVE FEEDBACK
3- white cliffs or Dovers made from liths come out
A small eukaryote (picoeuaryote) that is comparable in size to a girus
ostreococcus
ostreococcus can can get infected by virus leading only ________ viruses to be produced inside the cell due to space limitations
5-15
NCLDVs #2:
mimiviruses
mimi= mimicking microbe
mimiviruses infect:
amoeba cells
Mimivirus genome facts: (5 things)
1- linear dsDNA
2- has 900 nt inverted repeats at the ends (speculated to circulate during infection)
3- bigger than some bacterial genomes
4- found many genes that have never been found in a viral genome and are considered cellular genes
5- contain many translation genes but not enough to encode protein synthesis by itself
How did the genome of mimivirus get so big?
there are repeated gene and partial genome duplications (38% of the genome is from duplication events)
mostly at ends
Minivirus genome contains: (5 fun facts)
1- contains many genes not found in other viruses and considered cellular
2- contains genes recently acquired from cellular sources
3- contains many Orphan genes
4- contains many genes with evolutionary connections to other genes
5- contains many duplicated genes
Why is mimivirus so good at transmission?
having a large genome and a large virus structure allows amoeba to mistake it for bacterium and ingest it (taken into a phagosome) leading to infection
mimivirus strucrure
- star shaped at one vertex “stargate”
- multiple membrane layers
- long protein/sugar fibers that make it resemble bacteria
Under the stargate shaped there is ____ _________ and intead, it is filled with proteins that are involved in the first stages of infection
no DNA
once star-shaped vertex opens:
viral membrane and phagosome membrane fuse and DNA is released into cytoplasm
mimivirus replication and assembly happens in ______ _______ in the host cells cytoplasm and NOT in the nucleus like usual
viral factory
viruses released from edges of _____ _______
viral factory
how are viruses made in viral factories
DNA packaged into particles at the outside edge of the factory and it exits through a portal on the opposite end of the stargate opening
speculated that mimiviruses can cause ___________
pnemonia
people that get infected by viruses after being exposed to infected amoebae that act as _____ ________ to bring giruses into humans
trojan horses
even bigger viruses related to mimiviruses have been found called _______ and ________
mamavirus and megavirus
megavirus has ____% of its genome NOT similar to mimivirus
25
(same genes are in center and different genes are at end)
why are same genes are in center and different genes are at end
ends of genomes are hotspots for evolution while middle is more conserved and stable
Virophage (virus of a virus) Example:
Sputnik
sputnik replicates within an amoebae that is also infected with __________ as it replicates in its factory
mamavirus
Sputnik sometimes ends up in mamvirus particles and it can disrupt mamavirus replication and lead it to produce _______ ______
defective particles
Another girus ______ _____ ______ (____) infects marine protists that eats bacteria
cafeteria roenbergensis virus (CroV)
CroV infects a marine protist host that is analogous to amoeba but is a diff eukaryote and it can ALSO get infected by a virophage called ______
Mavirus
Mavirus exists as a _____ _______ in the eukartoyic microbe for defence
integrated element
provides defence to the cell against corresponding virus and are now found in eukaryotic genomes
Pandoraviruses ALSO infects ______ and is TWICE the size of mimivirus
amoebae
Pandoravirus VS mimivirus
- Both infect amoeba
- Both have membrane fusion function for opening the particle to release the DNA & virion contents into the cytoplasm similar to mimivirus stargate
- Both have the virus maturing in the infected cell starting at the apex going backwards to package DNA
BUT pandora x 2 the size
Pithovirus VS pandoravirus
- pithovirus even larger virion (but not that big of a genome!)
-pithovirus isolated from permafrost - both have structure on one end that mediates fusion with cells membrane to release contents into cytoplasm
- pithovirus has lattice structure when viewed straight on
Where did giruses come from?
1- bacterium infected by tectivirus was a endosymbiont that became mitochondria
2- tectivirus became a “polinton” (type of transposon) that was encoded in the nucleus
3- polinton escaped the nucleus and gained some cellular genes
4- the escaped version swapped genes and became the progenitor of mega viruses
5- polintons evolved more and became virophages adenoviruses bidnaviruses etc
many of girus genomes contain different _____ _____ ______ within them
mobile genetic elements (MGE)
proposed that MEGs are symbionts within the viral genome as they assist the virus in _____-______ ______ when there is many viruses trying to infect the same cell
virus-virus competition
(MEG makes virus win, virus wins, and MEG gets more distributed SYMBIOSIS)
Two types of MGE
1- restriction/modificatiom systems: degrade other viral DNA and host DNA and use it for their viruses replication
2-Homing endonuclease introns: splice out from genome and into the competing virus inactivating its genes/proteins
