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Microbiology > Taxonomy - viruses > Flashcards

Taxonomy - viruses Flashcards

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Biology 101 flashcards
1
Q

Viruses are grouped into __, given a __ name, and a __ name.

A

families ; genus ; species

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2
Q

Viruses are classified based on … (5)

A
  • nature of the host
  • type of disease caused
  • life cycle
  • naked or enveloped
  • types of nucleotides and strandedness
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3
Q

What is the Baltimore classification scheme based on?

A

Based on the type of genome

It is useful because the kind of genome dictates the replication mechanism.

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4
Q

If RNA genomes are:

  • on the same strand than mRNA, it is __
  • complementary to mRNA, it is __
A
  • plus configuration

- minus configuration

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5
Q

On which strand des it need to be transcribed into before it can be translated?

A
  • plus strand
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6
Q

What are the 6 stages of the life cycle of viruses?

A
  • adsorption = attachment of virus to specific receptors on the surface of the cell
  • penetration (injection) = virus genome enters the cell
  • uncoating
  • replication - of the nucleic acid, transcription and protein synthesis
  • maturation - assembly of virus components, nucleic acid, nucleocapsid and accessory proteins to form new virions
  • release - exit of host cell by mature virions by means of budding or by causing lysis of the cell
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7
Q

What is uncoating?

A

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

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8
Q

In enveloped and naked viruses, the complet __ can enter the cell.

A

virion

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9
Q

Naked viruses have no __. Everything is left at the __.

A

Envelope ; surface

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10
Q

In enveloped viruses, the __ is left at the surface.

A

Envelope

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11
Q

What do most enveloped viruses of eukaryotes use?

A

Endocytosis/ viropexis

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12
Q

Penetration by most enveloped virus = __. Such viruses are delivered to __ which degrade the __ and the __ is released in the cytoplasm.

A

viropexis ; lysosomes ; capsid ; nucleic acid

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13
Q

What is budding?

A

The release through membrane, acquisition of the envelope

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14
Q

What are the stages of virus replication?

A
  • latent period

- release/ rise period

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15
Q

What does the “latent period” consist of? (2)

A

Consists of eclipse + maturation.
Eclipse = time necessary for the host to replicate the viral genome and synthesise the viral components
Maturation = time needed for the components to be assembled

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16
Q

What is the “release period”?

A
  • Virions are detected outside the cell,
  • Lysis by virus-encoded proteins. These proteins damage peptidoglycan of bacteria and the cytoplasmic membrane of viruses.
  • Budding
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17
Q

What is the burst size?

A

The number of virions released.

It varies according to the virus, the host cell, etc.

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18
Q

What do the best bacteriophages studied infect?

A

E. coli (gram - bacteria)

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19
Q

What do most phages contain?

A

Linear dsDNA genome

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20
Q

What are the 2 types of bacteriophages?

A
  • virulent phages

- temporate phages

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21
Q

What is a virulent phage?

A

Infection of the host cell always leads to replication of resulting in host cell lysis (Lytic pathway only)
ex : T4

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22
Q

What options does a temperate phage have?

A

It has 2 options :
- lytic pathway
- lysogenic pathway where the genome becomes incorporated into the bacterial host genome
ex : lambda

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23
Q

Which bacteriophage

  • attaches to the core region of LPS (during adsorption) by the tail fibres
  • has the tail sheath that contracts through the outer membrane
  • tail lysozyme digest the peptidoglycan layer and form a pore
  • the phage DNA is then injected into the cytoplasm of the host cell
A

T4

24
Q

Infection by temperate phages results in a __ latent state of infection.

A

prolonged

25
Q

A phage genome within the host cell chromosome is a __.

A bacterium that contains a prophage is a __.

A

prophage; lysogen

26
Q

What is the process called when the prophage exits the chromosome and continues along the lytic pathway?

A

Excision.

It results in the production of new virus particles and host cell lysis.

27
Q

How is Lambda’s genome?

A
  • is linear dsDNA with cohesive ends

- cohesive ends join forming a circular molecule of dsDNA

28
Q

Where is Lambda’s genome integrated?

A

At a specific site in the bacterial chromosome : the attλ.

29
Q

What happens in replication of single-stranded DNA phage? For example replication of Phi X 174

A

the minus strand must be synthesised first to produce a dsDNA genome (the replicative form)

30
Q
  • What happens in replication of single-stranded RNA phage?

- What is the genome first used as?

A
  • Minus strand must be synthesised first.

- first used as an mRNA, it directs the synthesis of an RNA replicase and other viral proteins

31
Q

In eukaryotic cells where does DNA replication occur?

A

In the nucleus

32
Q

The genomes of :
- DNA viruses
- RNA viruses
will usually be replicated in the __ of the cell.

A
  • nucleus

- cytoplasm

33
Q
  • Examples of viral DNA.

- Where does assembly occur?

A
  • Herpesvirus; Papovirus

- in the nucleus, envelope is added via a budding process through the inner membrane of the nucleus

34
Q
  • Examples of viral + strand RNA

- How is the genome translated

A
  • Poliovirus ; Hepatitus A virus

- translated directly

35
Q

Example of a disease with no cure but a safe and effective vaccine that leads to skeletal deformities

A

Poliomyelitis

36
Q
  • Examples of viral - strand RNA

- How is the genome translated

A
  • measles, rabies (Rhabdovirus), Influenza (orthomyxovirus)
  • not translated directly, the RNA genome is first transcribed into a + strand RNA by an RNA dependent RNA polymerase carried inside virions
37
Q

Is there a safe and effective vaccine for measles?

A

Yes

38
Q
  • Examples of viral dsRNA

- How is the genome translated

A
  • Rotavirus (reovirus)

- The dsRNA genome can’t be translated as it, + strand must be synthesised and then translated to synthesise a - strand.

39
Q
  • Examples of viral retrovirus RNA

- where does the DNA genome travel to

A
  • HIV

- to the nucleus and is integrated in the host DNA

40
Q

Compare provirus and lambda prophage

A

provirus is integrated into the host

lambda prophage can’t excise from the host genome

41
Q
  • Examples of class I & VII (dsDNA +/- virus)

- Transcription

A
  • phage T4 (I), hepatitis B (VII)

- transcription of the minus strand leads to mRNA

42
Q
  • Examples of class II (ssDNA + virus)

- Transcription

A
  • phi X174, parvovirus

- synthesis of the minus strand leads to dsDNA intermediate (replicative form) leads to mRNA

43
Q
  • Examples of class III (dsRNA + virus)

- Transcription

A
  • phage phi 6, rotavirus

- transcription of the minus strand leads to mRNA

44
Q
  • Examples of class IV (ssRNA + virus)

- Transcription

A
  • phage MS2, poliovirus

- used directly as mRNA

45
Q
  • Examples of class V (ssRNA - virus)

- Transcription

A
  • rabies virus, influenza virus

- transcription of the minus strand, leads to mRNA

46
Q
  • Examples of class VI (ssRNA + retrovirus)

- Transcription

A
  • HIV, mouse leukemia virus

- reverse transcription leads to dsDNA intermediate, leads to transcription of minus strand, leads to mRNA

47
Q

__ viruses

  • Class I : classical __
  • Class II : classical __, discard __ strand
  • Class VII : transcription followed by __ transcription
A
  • DNA
  • semiconservative
  • semiconservative, (-)
  • reverse
48
Q

__ viruses

  • Class III : make ssRNA __ and transcribe from this to give ssRNA __ complementary strand
  • Class IV : make ssRNA __ and transcribe from this to five ssRNA __ genome
  • Class V : make ssRNA __ and transcribe from this to give ssRNA __ genome
  • Class VI : make ssRNA __ genome by transcription of __ strand of __
A
  • RNA
  • (+) ; (-)
  • (-) ; (+)
  • (+) ; (-)
  • (+) ; (-) ; dsDNA
49
Q

Enveloped viruses that fuse with the host cell cytoplasmic membrane carries __ that fuse biological membranes

A

viral proteins

50
Q

What does cell fusion result in?

A

In hybrid cells that have chromosomal aberrations and are usually short-lived

51
Q

What is a tumor cell?

A

A cell that has acquired immortality, characterised by uncontrolled replication (=transformation

52
Q

Which viruses are known to cause tumours in animals and humans?

A
  • both DNA & RNA viruses
53
Q

4 different mechanisms of oncogenic/tumor-producing viruses

A
  1. transduction of an oncogene (v-oncogene)
  2. insertion of a strong promoter upstream of a proto-oncogene
  3. inactivation of a tumor suppressor gene by insertion of the provirus
  4. expression of a viral protein that induces transformaton (DNA virus)
54
Q

__ % of all human cancers are associated with 1 of 5 viruses :

  • Epstein-Barr virus (DNA)
  • Hepatitis C virus (RNA)
  • Human T-lymphotropic virus type 1 (retrovirus)
  • Hepatitis B virus (RNA)
  • Human papilloma virus (DNA)
A

15-20%

55
Q

In the case of HPV, viral genome integrates in __ genome which leads to over expression of __, cell __ and formation of a __.

A
  • host
  • E6 and E7
  • proliferation
  • tumor

Microbiology (6 decks)

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