Section 4

Question 1

Giant viruses are called:

Answer 1

Nucelocytoplasmic large DNA viruses (NCLDVs)

Question 1

NCLDVs facts

Answer 1

• 6 families
• large ds DNA geomes
• share sets of “core” genes

Question 2

NCLDVs #1:

Answer 2

Phycodnaviruses

Question 3

Phycodnaviruses

Answer 3

viruses that infect algea (best studied eukaryotic viruses)

Question 4

Phycodnaviruses (PBCV-1) infect:

Answer 4

Chlorella alga symbionts that live in paramecium

Question 5

Phycodnaviruses (PBCV-1) stands for

Answer 5

paramecium bursary chlorella virus

Question 6

PBCV-1 structure:

Answer 6

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

Question 7

Inside PBCV-1 virion at the vertex where the spike is looks different because

Answer 7

it has lower density than rest of the virion due to more packaged protein and less DNA

Question 8

PBCV-1 attaches to virus at spike and makes a _____ through the algae cell wall then proteins are released into the cells cytoplasm

Answer 8

hole

Question 9

Phycodnaviruses have been found in ______ and show decline in performance on cognitive tests

Answer 9

brain

Question 10

Mice that were infected with virus containing algae showed: (3 things)

Answer 10

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

Question 11

algae that have chalk plates on the outside of their cells: __________

viruses that infect this chalk type of algae: _____________

Answer 11

coccolithophores

cocolithoviruses

Question 12

coccolithophores form:

Answer 12

large blooms in ocean seen from space due to their chalky exterior
when blooms end, lots of cocolithoviruses are found in seawater

Question 13

cocolithoviruses (ex. EhV-86) encode

Answer 13

proteins that synthesize the sphingolipid ceramide

Question 14

sphingolipid ceramide from cocolithoviruses are involved in: (2 things)

Answer 14

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

Question 15

effect of cocolithovirsues on climate

Answer 15

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

Question 16

A small eukaryote (picoeuaryote) that is comparable in size to a girus

Answer 16

ostreococcus

Question 17

ostreococcus can can get infected by virus leading only ________ viruses to be produced inside the cell due to space limitations

Answer 17

5-15

Question 18

NCLDVs #2:

Answer 18

mimiviruses

mimi= mimicking microbe

Question 19

mimiviruses infect:

Answer 19

amoeba cells

Question 20

Mimivirus genome facts: (5 things)

Answer 20

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

Question 21

How did the genome of mimivirus get so big?

Answer 21

there are repeated gene and partial genome duplications (38% of the genome is from duplication events)

mostly at ends

Question 22

Minivirus genome contains: (5 fun facts)

Answer 22

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

Question 23

Why is mimivirus so good at transmission?

Answer 23

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

Question 24

mimivirus strucrure

Answer 24

- star shaped at one vertex "stargate" - multiple membrane layers - long protein/sugar fibers that make it resemble bacteria

Question 25

Under the stargate shaped there is ____ _________ and intead, it is filled with proteins that are involved in the first stages of infection

Answer 25

no DNA

Question 26

once star-shaped vertex opens:

Answer 26

viral membrane and phagosome membrane fuse and DNA is released into cytoplasm

Question 27

mimivirus replication and assembly happens in ______ _______ in the host cells cytoplasm and NOT in the nucleus like usual

Answer 27

viral factory

Question 28

viruses released from edges of _____ _______

Answer 28

viral factory

Question 29

how are viruses made in viral factories

Answer 29

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

Question 30

speculated that mimiviruses can cause ___________

Answer 30

pnemonia

Question 31

people that get infected by viruses after being exposed to infected amoebae that act as _____ ________ to bring giruses into humans

Answer 31

trojan horses

Question 32

even bigger viruses related to mimiviruses have been found called _______ and ________

Answer 32

mamavirus and megavirus

Question 33

megavirus has ____% of its genome NOT similar to mimivirus

Answer 33

25 (same genes are in center and different genes are at end)

Question 34

why are same genes are in center and different genes are at end

Answer 34

ends of genomes are hotspots for evolution while middle is more conserved and stable

Question 35

Virophage (virus of a virus) Example:

Answer 35

Sputnik

Question 36

sputnik replicates within an amoebae that is also infected with __________ as it replicates in its factory

Answer 36

mamavirus

Question 37

Sputnik sometimes ends up in mamvirus particles and it can disrupt mamavirus replication and lead it to produce _______ ______

Answer 37

defective particles

Question 38

Another girus ______ _____ ______ (____) infects marine protists that eats bacteria

Answer 38

cafeteria roenbergensis virus (CroV)

Question 39

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 ______

Answer 39

Mavirus

Question 40

Mavirus exists as a _____ _______ in the eukartoyic microbe for defence

Answer 40

integrated element provides defence to the cell against corresponding virus and are now found in eukaryotic genomes

Question 41

Pandoraviruses ALSO infects ______ and is TWICE the size of mimivirus

Answer 41

amoebae

Question 42

Pandoravirus VS mimivirus

Answer 42

- 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

Question 43

Pithovirus VS pandoravirus

Answer 43

- 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

Question 44

Where did giruses come from?

Answer 44

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

Question 45

many of girus genomes contain different _____ _____ ______ within them

Answer 45

mobile genetic elements (MGE)

Question 46

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

Answer 46

virus-virus competition (MEG makes virus win, virus wins, and MEG gets more distributed SYMBIOSIS)

Question 47

Two types of MGE

Answer 47

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