If RNA genomes are: - on the same strand than mRNA, it is __ - complementary to mRNA, it is __

- plus configuration - minus configuration

Taxonomy - viruses Flashcards by Olivia Pouret

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

families ; genus ; species

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Viruses are classified based on … (5)

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

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What is the Baltimore classification scheme based on?

Based on the type of genome

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

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If RNA genomes are:

on the same strand than mRNA, it is __
complementary to mRNA, it is __

plus configuration

- minus configuration

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

plus strand

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

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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What is uncoating?

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

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

virion

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

Envelope ; surface

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

Envelope

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What do most enveloped viruses of eukaryotes use?

Endocytosis/ viropexis

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

viropexis ; lysosomes ; capsid ; nucleic acid

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What is budding?

The release through membrane, acquisition of the envelope

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What are the stages of virus replication?

latent period

- release/ rise period

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

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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What is the “release period”?

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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What is the burst size?

The number of virions released.

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

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What do the best bacteriophages studied infect?

E. coli (gram - bacteria)

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What do most phages contain?

Linear dsDNA genome

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What are the 2 types of bacteriophages?

virulent phages

- temporate phages

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What is a virulent phage?

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

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What options does a temperate phage have?

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

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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

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

prolonged

A phage genome within the host cell chromosome is a __. | A bacterium that contains a prophage is a __.

prophage; lysogen

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

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

How is Lambda's genome?

- is linear dsDNA with cohesive ends | - cohesive ends join forming a circular molecule of dsDNA

Where is Lambda's genome integrated?

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

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

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

- What happens in replication of single-stranded RNA phage? | - What is the genome first used as?

- Minus strand must be synthesised first. | - first used as an mRNA, it directs the synthesis of an RNA replicase and other viral proteins

In eukaryotic cells where does DNA replication occur?

In the nucleus

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

- nucleus | - cytoplasm

- Examples of viral DNA. | - Where does assembly occur?

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

- Examples of viral + strand RNA | - How is the genome translated

- Poliovirus ; Hepatitus A virus | - translated directly

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

Poliomyelitis

- Examples of viral - strand RNA | - How is the genome translated

- 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

Is there a safe and effective vaccine for measles?

Yes

- Examples of viral dsRNA | - How is the genome translated

- Rotavirus (reovirus) | - The dsRNA genome can't be translated as it, + strand must be synthesised and then translated to synthesise a - strand.

- Examples of viral retrovirus RNA | - where does the DNA genome travel to

- HIV | - to the nucleus and is integrated in the host DNA

Compare provirus and lambda prophage

provirus is integrated into the host | lambda prophage can't excise from the host genome

- Examples of class I & VII (dsDNA +/- virus) | - Transcription

- phage T4 (I), hepatitis B (VII) | - transcription of the minus strand leads to mRNA

- Examples of class II (ssDNA + virus) | - Transcription

- phi X174, parvovirus | - synthesis of the minus strand leads to dsDNA intermediate (replicative form) leads to mRNA

- Examples of class III (dsRNA + virus) | - Transcription

- phage phi 6, rotavirus | - transcription of the minus strand leads to mRNA

- Examples of class IV (ssRNA + virus) | - Transcription

- phage MS2, poliovirus | - used directly as mRNA

- Examples of class V (ssRNA - virus) | - Transcription

- rabies virus, influenza virus | - transcription of the minus strand, leads to mRNA

- Examples of class VI (ssRNA + retrovirus) | - Transcription

- HIV, mouse leukemia virus | - reverse transcription leads to dsDNA intermediate, leads to transcription of minus strand, leads to mRNA

__ viruses - Class I : classical __ - Class II : classical __, discard __ strand - Class VII : transcription followed by __ transcription

- DNA - semiconservative - semiconservative, (-) - reverse

__ 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 __

- RNA - (+) ; (-) - (-) ; (+) - (+) ; (-) - (+) ; (-) ; dsDNA

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

viral proteins

What does cell fusion result in?

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

What is a tumor cell?

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

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

- both DNA & RNA viruses

4 different mechanisms of oncogenic/tumor-producing viruses

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)

__ % 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)

15-20%

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

- host - E6 and E7 - proliferation - tumor