Taxonomy of viruses Flashcards

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1
Q

Virus are given 3 different names…

A
  • Into FAMILIES: end in viridae
  • Viruses are given a genus name : end in virus
  • Viruses are given a species name: Usually in english, descriptive
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2
Q

Classification of viruses is based on different characteristics. Name them…

A
  • Nature of the host (ex: bacteriophage infect bacteria)
  • Type of disease caused (ex: murine leukemia virus)
  • Life cycle (pathways of nucleic acid replication and transcription)
  • Naked or enveloped
  • Type of nucleic acids and strandedness (+ strand = same as mRNA)
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3
Q

What is the baltimore classification scheme?

A

-Scheme where classification is based on the type of genome. It is useful because THE KIND OF GENOME WILL DICTATE THE REPLICATION MECHANISM.

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4
Q

What are RNA genomes?

A

+ configuration: Same strand than mRNA (can be translated directly)

  • configuration: complementary to mRNA (needs to be transcribed into + strand before it can be translated)
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5
Q

What are the 5 steps of the life cycle of viruses?

A
  • Attachment ( absorption)
  • Penetration
  • Synthesis of nucleic acid and prots
  • Assembly and packaging
  • Release (lysis)

OR

  • Absorption
  • Penetration
  • Uncoating
  • Replication
  • Maturation
  • Release
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6
Q

What happens during the penetration step of a viruses life cycle?

A

The virus genome enters the cell:

  • In ENVELOPED AND NAKED VIRUSES: the complete virion ma enter the cell
  • In ENVELOPED viruses , the envelope may be left at the surface of the cell, such that only the nucleocapsid enters the cell
  • In NAKED viruses, the nucleocapsid may be left at the surface
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7
Q

What is uncoating in the life cycle of the virus?

A

removal of the envelope and/or the nucleocapsid by host enzymes, sometimes within lysosomes (in eukaryotes)

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8
Q

What are the 3 penetration method used by viruses?

A
  • Direct penetration
  • Membrane fusion
  • Endocytosis
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9
Q

What penetration method is most commonly used by ENVELOPED VIRUSES OF EUKARYOTES?

A

Most enveloped viruses of eukaryotes use endocytosis (VIROPEXIS). Such viruses are then delivered to lysosomes which degrade the nucleocapsid and the nucleic acid is released into the cytoplasm.

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10
Q

What happens during the maturation phase of lice cycle of viruses?

A
  • assembly of virus components, nucleic acid, nuceloapsid and accessory prots to form new virions
  • Usually, the assembly is spontaneous
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11
Q

What happens during the release phase of life cycle of viruses?

A
  • Mature virions exit the host cell by means of BUDDING or by causing lysis of the cell. Plant viruses exit and are transmitted by means of vectors.
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12
Q

What are the main phases ( on the curve) of virus replication ? What subphase does it include?

A

Latent Phase: eclipse + maturation

  - ECLIPSE : time necessary for the host cells to replicate the viral genome and to synthesize the viral components 
 - MATURATION : time needed for the different components to be assembled. 

Release phase (RISE period)

 - Virions are detected OUTSIDE the cell
 - LYSIS : damage of cytoplasm (in bacteria, destroy peptidoglycan layer)
 - BUDDING: developed virus
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13
Q

What is the definition of Burst size?

A

Number of virions released

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14
Q

What type of DNA do most of the phages contain?

A

Most of the phages contain LINEAR dsDNA genomes. Most are NAKED, but some possess lipid envelope.

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15
Q

What are the 2 pathways of a viral life cycle?

A

LYTIC PATHWAY: in virulent phages, replication results in host cell lysis–> T4

LYSOGENIC PATHWAY: in temperate phages, the genome becomes incorporated into the bacterial host genome –> Lambda

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16
Q

What type of phage is T4 bacteriophage?

A

Virulent phage

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17
Q

How does bacteriophage T4 invade a host?

A
  • Absorption: T4 attaches to core region of LPS by the tail fibers
  • Tail sheath contracts, force central core through outer membrane. LYSOSYMES of the tail digest peptidoglycan layer, forming a pore
  • The phage DNA is then injected into the cytoplasm of the host cell.
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18
Q

How do we call a prolonged, latent state of infection?

A

lysogeny

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19
Q

What kind of phage is Lambda?

A

temperate phage

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20
Q

What is a prophage?

A

Phage genome within the host cell chromosome

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21
Q

What is Lysogen?

A

bacterium that contains a prophage

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22
Q

What are the 2 pathways possible in the infection of Lambda bacteriophage?

A

Lytic pathway and lysogenic pathway (see slides…)

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23
Q

True or false

Prophages can never exit the chromosome of the host.

A

False. Prophage can exit the chromosome (a process called EXCISION) and continue along the lytic pathway, resulting in the production of NEW VIRUS PARTICLES, and HOST CELL LYSIS.

24
Q

Describe the genome of Lambda.

A
  • linear dsDNA with cohesive ends, a region of ss complementary DNA
25
Q

aller voir la slide qui parle de labda replication, tout le process

A

GO

26
Q

What kind of phage is MS2 phage?

A

it is a + strand RNA phage

27
Q

What is the process of replication of MS2 genome?

A
  • genome is used as mRNA
  • direct synthesis of and RNA REPLICASE (RNA-dependant RNA polymerase, fct not performed by the host) and other viral prots
  • RNA replicase synthesize a minus strand RNA is used to produce additional mRNA and additional copies of genome (+ strand) for the production of new virions)
28
Q

Where does DNa replication occur in eukaryotic cells?

A

Nucleus

29
Q

Where does the genome of DNA viruses be replicated in animal viruses?

A

nucleus

30
Q

Where does the genome of RNA viruses be usually replicated in animal viruses?

A

in the cytoplasm

31
Q

Give an exemple of DNA virus

A

herpesvirus

32
Q

Give and exemple of RNA genome viruses + strand RNA

A

Poliovirus and hepatisis A

33
Q

Go check RNA genome 1- poliovirus

A

Go

34
Q

Give an exemple of RNA genome -minus strand RNA

A

Measles, Influenza, Rhabdovirus

35
Q

how is a - strand RNA transcribed?

A
  • First transcribed into + strand RNA by RNA-dependant RNA polymerase carried inside the virions
36
Q

Give an exemple of RNA genome dsRNA of a virus

A

Rotavirus

37
Q

Explain the transcription of dsRNA genome of a virus

A
  • the dsRNA genome cannot be transcribed
  • First, the + strand RNA must be transcribed using RNA-DEPENDANT RNA POLYMERASE using the MINUS STRAND as the template

+ strand is then translated into prots and is used as template to produce - strand to yield dsRNA genomes

38
Q

Give an exemple of retrovirus RNA genome

A

HIV

Causing cancer= Rous sarcoma virus

39
Q

What is reverse transcriptase?

A

Reverse transcriptase is a RNA-dependant DNA polymerase that reverse transcribes the RNA genome into DNA

40
Q

What does retrovirus virions carry

A
  • 2 identical copies of the genome (+ strand ssRNA )
  • Reverse transcriptase
  • Integrases
  • Proteases
41
Q

Where does the DNA genome transcribed from retrovirus (+strand RNA) go?

A

DNA genome travels to the nucleus and is intergrated into the host cell DNA

42
Q

What is LTR?

A

Long terminal repeats

It contains the promoter for transcription and participate n the integration process

43
Q

What is a Provirus?

A

It is an integrated viral DNA . Contrary to the lambda prophage, the provirus cannot be excise from the host genome.

44
Q

What are the consequences of viral infection in animals?

A

Can lead to :

Attachment and penetration
- Cell fusion

Virus multiplication:

  • Virus present but not replicating —> LATENT INFECTION
  • Slow release of virus without cell death —> PERSISTANT INFECTION
  • Death of cell and release of virus—> LYSIS

Transformation into tumor cell:
- Tumor cell division–> TRANSFORMATION

45
Q

What is cell fusion

A

When virus causes 2 cells to fuse. Results in hybrid that has chromosomal aberrations. Are usually short-lived.

46
Q

What are 4 different mechanism of tumor producing viruses?

A
  • Transduction
  • Insertion of a strong promoter
  • Inactivation of a tumor suppressor gene
  • Expression of a viral protein that induces transformation (DNA virus)
47
Q

Explain transduction in tumor producing mechanism

A
  • RNA virus
  • Rous Sarcoma virus
  • Virus carries many oncogenes ( tumor-causing genes) called v-oncogens
  • v-oncogen is acquired from the host
  • High expression of the oncgene affects the regulation of replication and/or cell death and causes transformation
48
Q

Explain insertion of a promoter in tumor producing mechanism

A
  • RETROVIRUS
  • virus doesn’t encode oncogene
  • voir la slide
49
Q

Explain inactivation of a tumor suppressor gene in tumor producing mechanism

A
  • RETROVIRUS
  • the virus does’nt encode oncogene
  • Insertion of a provirus in a gene involved in the regulation of the proto-oncogene
  • Inactivation of proto-oncogene
  • uncontrolled expression of the proto-oncogene
50
Q

Explain expression of a viral protein in tumor producing mechanism

A
  • DNA virus
  • Viral protein doesn’t have a cell counterpart
  • Integration of the viral genome into the host genome may occur, or the viral genome may persist in the cell as an extrachromosomal episome
  • VOIR LA SLIDE
51
Q

What is C-oncogen

A
  • also called proto-oncogen

- involved in the regulation of the cell cycle or in safety mechanisms that prevent transformation

52
Q

What is transformation? (oncogenic/tumor providing viruses)

A

Conversion of a normal cell into a tumor cell–> cell that has acquire immortality, characterized by UNCONTROLLED REPLICATION

53
Q

What are the steps of replication of a single DNA phages genome?

A

THE STRAND IS POSITIVE

  1. Copy a negative strand using the positive strand
    - dsDNA being the replicative form
  2. The positive strand is cut
  3. Derolling of the olad postivite strand and new positive strand produced

products:
dsDNA strand and postive DNA strand

54
Q

Can ssRNA of MS2 be replicated by the host cell?

A

NO!

Because the cell doens’t have the function to replicate RNA strands… RNA replicase (RNA-dependant RNA polymerase is provided by the phage!)

55
Q

What are the steps of replication of a ssRNA phage?

A
  1. synthesis of minus strand by RNA replicase

2. Use of minus strand to produce more positive strand

56
Q

Can the ssRNA phage of MS2 be translated right away?

A

Yes, because it is a plus-strand, so has the same structure as mRNA

57
Q

An exemple of DNA virus?

A

Human papilloma virus