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BIOL 4010 Virology > Section 5 > Flashcards

Section 5 Flashcards

1
Q

Plant viruses have the longest history in virology because

A

first virus discovered is the TMV (tobacco mosaic virus)

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2
Q

Most plant viruses are ______ genomed and there is no normal dsDNA viruses

A

RNA

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3
Q

plant viruses have diff particle morphologies but high occurrence of _________ structures
and some are related to animal or protist viruses

A

filamentous

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4
Q

Plant virus common characteristics:

A

1- most plant virus capsids are made of single protien
2- most are icosohedral
3- most have evolved to get their lipid layer from the cells membrane
4- most geminate making “pairs” of two capsids that come together

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5
Q

Some plant viruses are shaped like a bacillus (rod) called ________ that are helical and filamentous

A

bacilliform

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6
Q

TMV characteristics

A

1- perfectly regular helical shape
2- showed that RNA encodes protein
3- good model virus
4- very stable
5- replicates to high density and easy to purify a lot
6- has ONLY two components: RNA genome and capsid protien

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7
Q

packaging of TMV does not start at the end but rather, the RNA has a specific sequence that makes ________ where it goes in first

A

hairpins

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8
Q

TMV packaging stages

A

1- RNA specific structure forms hairpin
2- hairpin goes in and forms into a helical structure as protein (capsid) wraps around the outside
3- RNA is fed through the bottom of the capsid as it assembles toward the 5’ end

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9
Q

TMV will spontaneously assemble in vitro when the RNA and capsid protein are mixed together meaning no ____ are required

A

cofactors

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10
Q

TMV is a great example of efficient use of limited genome size because it encodes _____ different proteins that are

A

4 different proteins:
2- versions of the non-structural replication protein
- short version ORF1 is a helices required for efficient replication
- long version ORF2 has RdRp region for RNA synthesis**

** (made in smaller amounts cuz ribosome passes through stop codon after ORF1)

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11
Q

the 4 protiens are:

A
  • 2- versions of the non-structural replication protein

and

  • 2 protiens translated from subgenomic RNAs
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12
Q

2- versions of the non-structural replication protein are:
(for making -ve sense RNA)
(don’t go into cell)

A
  • short version ORF1 is a helices required for efficient replication
    - long version ORF2 has RdRp region for RNA synthesis**

** (made in smaller amounts cuz ribosome passes through stop codon after ORF1)

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13
Q
  • 2 protiens translated from subgenomic RNAs means:
A

this means translation of ORF1-2 from the genomic RNA
needs to happen after infection, and then the RdRp can make
a –ve sense version of the RNA and the sub-genomic RNAs
can be transcribed from that -ve sense copy by RdRp
individual promoters before those ORFs for their transcription

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14
Q
  • 2 protiens translated from subgenomic RNAs are
A

CP = capsid protein, MP = movement protein

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15
Q

How do viruses move within plants?
(not like animals where they spread within the host as assembled particles)

A

initial local movements between
neighboring cells (without even making complete virions) by MP
followed later by systemic transmission through the plants’ circulatory system (phloem)

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16
Q

what does MP “movement protein” do?

A

MP = movement protein: allows infection of neighboring
cells by transporting the viral RNA between cells

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17
Q

what happens if virus that does have ORF for CP gets injected?

A

can spread to neighbouring cells within
the plant but there will not be a systemic infection

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18
Q

viral RNA moves through plant cell structures called __________ (with the requirement of MP)

A

plasmodesmata

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19
Q

neither the MP nor viral RNA can pass through
plasmodesmata on their own but when ________, they get through

A

together

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20
Q

MP binds to the viral ssRNA in
_______ regions to move them between plasmodesmata

A

non-folded

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21
Q

some spherical viruses move between
cells as complete __________
where MP forms a ______ through the
plasmodesmata

A

nucleocapsids
tube

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22
Q

Cucumber mosiac virus fun facts (2):

A
  • largest host range of any known virus (infects >1200 species of plants)
  • infects crops worldwide and is a problem for agriculture
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23
Q

why is cucumber mosaic virus a good model virus

A
  • can infect cells by injecting RNA (without having to make virus particles)
  • high yields of particles
  • infects plant cell protoplasts (plant cell cultures, don’t need whole plant)
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24
Q

Cucumber mosiac virus genome is

A

+ve ssRNA segmented genome
RNAs 1, 2, ,3 required for infection

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25
Q

Cucumber mosiac virus also makes

A

also makes subgenomc RNAs during infection for protein synthesis

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26
Q

Cucumber mosiac virus:
RNAs 1 and 2 are _____ ______
whereas
RNAs 3 and 4 are also _____ _______

(RNA 4 can be made, doesn’t need to come in virion “sub-genomic”)

A

packaged together

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27
Q

Cucumber mosiac virus needs 3 visions to be transmitted for infection making it a ___-______ ____

A

multi-partite virus (segmented genome)

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28
Q

cellular enzymes think CMV RNA is tRNA and add an amino acid to it because

A

3’ ends of CMV fold into tRNA like pseudoknot

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29
Q

CMV folding into tRNA like pseudoknot to trick the cell for many reasons (3):

A
  1. protect RNA from being degraded by nucleases
    2- increase translation of RNA
    3- help avoid RNA replication on RNAs that are being translated
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30
Q

CMV encodes ___ proteins

A

FIVE

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31
Q

the five CMV protiens are

A

2 replicase
1 movement within plant and immunity against host defences
1- movement
1 capsid

32
Q

where does CMV RNA replication occur?

A

in membrane vesicles attached on the inside of cells vacuole (gas chamber)

(membrane vesicles made by viral proteins and they bring the RNA template there)

33
Q

How does CMV RNA replication happen in membrane vesicle

A

replicase interacts with sequences in 5’ and 3’ region of the RNA to initiate replication (also requires host protiens)

34
Q

WHY does CMV RNA replication occur in membrane vesicles

A

to keep viral RNA out of cytoplasm and away from anti dsRNA defense

35
Q

Turnip Yellow Mosaic virus also uses intracellular vesicles to replicate, the vesicle is

A

outer membrane of chloroplasts

36
Q

TMV makes vesicles in

A

endoplasmic reticulum

37
Q

replication in vesicles is an old strategy as it occurs in primitive cells (ancestors of plants) such as ______ that replicates in vesicles around edges of ER

A

HaRNAV (relative of polio) infects unicellular photosynthetic protists

38
Q

_________ forms harmful algal blooms and releases a toxin that kills fish

A

HaRNAV

39
Q

Geminiviruses (NEW!) increase packaging size of their simple visions because they have

A

2 icosahedrons fused together

40
Q

Geminiviruses (due to their 2 fused icosahedrons)

A

can package -3000 bases of circular ssDNA and increase the amount of nucleic acid they can package (some are made of 2 pieces of DNA each in separate capsids and both need to be transmitted for infection)

41
Q

some Geminiviruses are made of 2 pieces of DNA each in separate capsids and both need to be transmitted for infection making them ALSO _____-______

A

multi-partite

42
Q

Geminiviruses do not encode their own _____ so so are
dependent on the host enzymes
DNA polymerase for synthesis of the
dsDNA version from ss genome that enters the cell from virion

A

polymerases

43
Q

once Geminiviruses use the cells DNA pol to make dsDNA from the ssDNA that enters the cell, this dsDNA then becomes: (2 things)

A

1- template for transcription (by host
RNA pol)

2- replication of more ssDNA genome copies for packaging into new virions

44
Q

Geminiviruses have ___________ _____
that go in two directions away
from the intergenic region (IR, top)

A

overlapping genes

45
Q

________ _______ (IR) contains (no protein coding) important sequences for replication and gene expression

A

intergenic region

46
Q

commonalities of geminivirus with TMV and
CMV, even though it is a ssDNA
virus as opposed to RNA

A

MP
CP
and Replication protein(s) (don’t do the replication but make it happen)

47
Q

Key viral protein for geminivirus is _____ that brings cells host DNA pol to perform rolling circular replication

A

Rep

48
Q

after Rep is done, it displaces the __ _____ _______ circles that are packaged

A

+ve ssDNA

49
Q

Rep binds to a specific sequence in ____ near the stem loop structure and it makes a _____ in the loop portion making the 3’ end needed for DNA synthesis

A

IR
cut

50
Q

IR also has promotors for transcription called _________ boxes on both sides to allow gene expression in two directions

A

TATAA

51
Q

after completion of a replication cycle, +ve sense DNA circle (template) gets sent back (released)

and new stand gets ______ by Rep to make it into a closed circle (can be packaged or used to make more DNA)

A

ligated

52
Q

________ have 10 individual ssDNA circles that make up the genome and package each into its own icosahedral capsid

A

nanoviruses

53
Q

plant cells have thick walls which makes it difficult for a virus to get through so they use _____ _______ to break through the plant cell wall and allow transmission

A

other organisms (ex. insects that feed on plants, ex. worms)

54
Q

The transmission insects for each viruses are very ____ and _____

A

specific and limited (ones that feed on that plant)

55
Q

transmission of plants can also occur vertically through:

A

seed via infected pollen or ovule

56
Q

Types of insect transmitted plant viruses

A

propagative
non-circulative
circulative

57
Q

Some plant viruses replicate in plant AND in transmission vector species called __________

A

propagative

58
Q

Others just stick to the mouth part of the insect and get transmitted to the next plant it eats called ____-______

A

non-circulative

59
Q

finally, some intermediate ones move within the insect and pass through cells and tissues but don’t replicate in insect called _________

A

circulative

60
Q

Insect transmitted viruses need to be able to interact with _____ ______ cells AS WELL AS the _______ that will carry them by having receptors for that vector on their capsid

A

plant host

vector

61
Q

Cucumber necrosis virus (CNV) is transmitted between plants by _____

A

Fungus

62
Q

sub viral pathogenic agents common in plants are (2)

A

satellites
viroids

63
Q

satellites

A
  • require helper virus for replication (but they are not required for the replication of the helper virus and they don’t share sequence homology with it)
  • do not encode their own protiens for replication (in plants)
64
Q

satellite viruses

A

encode their own capsid protein that packages the genome but need help for replication

65
Q

satellite nucleic acids

A

packaged in helper protein capsid

66
Q

satellite are _____ of helper

A

parasites

67
Q

satellites effect the diseases caused by helper sometimes __________ it and sometimes ________ it

A

attenuating it
making it more severe

68
Q

satalties are not a ___________ taxonomic group
they have dsRNA ssDNA and circular ssRNA

A

homogenous

69
Q

satellite tobacco mosaic virus (STMV) has ________ genome and and has 3’ untranslated region UTR

similar to that of TMV so that when TMV replicates it replicates the satellite too by accident

A

ssRNA

UTR

70
Q

STMV encodes 2 proteins:

A

1- unknown function
2- capsid

71
Q

STMV causes _________ disease symptoms of TMV

A

enhanced

72
Q

there are satellites that don’t encode proteins but compete w viral RNA for replicase enzyme and packaging called _________

A

non-messenger satellite RNAs

73
Q

non-messenger satellite RNAs example

folds into structure that is recognizable by CMV replicase

A

satelite cucumber mosaic virus

74
Q

Viriods:

A
  • only exist as generic material (not packaged inside capsids)
  • exist as ssRNA molecules
  • get transmitted mechanically (attached through something and penetrate the cell wall) through machines etc
75
Q

viroids are _______ but fold to look like double stranded RNA circle (rod shape)

A

ssRNA

76
Q

you can tell viroids by their sequences

A
77
Q

beneficial plant viruses (2)

A
  1. endogenous pararetroviruses: (package DNA) and protect against infection by exogenous pararetroviruses
  2. plants infected with some viruses are more resistant to cold temps
  3. virologists found a fungal virus that is beneficial to plants (grass can survive over 50 deg if it has been infected by fungal virus)

BIOL 4010 Virology (20 decks)

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