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Microorganisms, Infection, Immunity > Diversity and Biology of Viruses > Flashcards

Diversity and Biology of Viruses Flashcards

1
Q

What is the most important criteria for virus classification?

  • Nature and sequence of nucleic acid genome
  • Symmetry of capsid
  • Presence of a lipid envelope
  • Type of cell/organism that the virus infects

quiz

A
  • Nature and sequence of nucleic acid genome

Viral genomes can be either DNA or RNA, double stranded or single stranded, linear, circular or segmented. Together with the nucleic acid sequence, this is the most accurate way of classifying viruses. The capsid symmetry (icosahedral, helical, or complex) and presence/absence of a lipid envelope are also used for classification.

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2
Q

What is the common phenomenon in all viral infections?

  • DNA replication
  • mRNA synthesis
  • Glycoprotein synthesis
  • RNA dependent-DNA synthesis

quiz

A
  • mRNA synthesis

Viruses are dependent on the host cell for synthesis of viral proteins through ribosomal translation of mRNA. All viruses regardless of whether they have an RNA or DNA genome need to produce mRNA. This is the basis for the Baltimore classification, which classifies viruses based on how they produce mRNA from their genomes.

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3
Q

Differentiation of enveloped and non enveloped viruses are related to the presence or absence of…?

  • Nucleic acid
  • Lipids
  • Proteins
  • Enzymes

quiz

A

-Lipids

An enveloped virus has a lipid membrane surrounding its capsid. This is derived from the host cell plasma membrane when the virus exits the cell by budding. Non enveloped viruses exit the cell by lysis of the host cell, or by using the host cell secretory machinery.

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4
Q

Which of these viruses has helical symmetry?

-Adenovirus
-Influenza virus
-Herpesvirus
-Parvovirus

quiz

A
  • Influenza

Influenza viruses have 8 segments of genomic RNA associated with the virus encoded nucleoprotein arranged in a helical formation.

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5
Q

Which of these viruses has icosahedral symmetry?

-Herpesvirus
-Poxvirus
-Ebola virus
-Picornavirus

quiz

A
  • Herpes
  • Picornavirus

Herpesviruses have large icosahedral capsids surrounded by a lipid envelope. The capsid contains a double stranded DNA genome of 100-200kbp encoding 80+ genes. The picornaviruses have a small non-enveloped icosahedral capsid protecting a small single stranded RNA genome (~8kbp) encoding 4 structural (capsid) proteins and 7 non-structural (replication) proteins.

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6
Q

Which of the following is a TRUE statement about viruses?

-Contain both DNA and RNA
-May have an envelope
-Have their own metabolism
-May contains enzymes for replication
-Have a cell wall

qiuz

A

-May have an envelope
-May contains enzymes for replication

Viruses are metabolically inert particles that require entry into a host cell for replication. Their genomes can be made up from DNA or RNA, and some viruses carry specific enzymes essential for their replication such as RNA-dependent RNA polymerases or RNA-dependent DNA polymerases (reverse transcriptase) that are not found in host cells.

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7
Q

In a one-step growth assay, the “Eclipse period” is…?

-The time taken between infection of cell and the appearance of extracellular virus particles

-The time taken between infection of cell and the appearance of intracellular virus particles

-The time taken between infection of cell and the maximum production of virus particles

-The time taken for a virus to infect a cell

quiz

A

-The time taken between infection of cell and the appearance of intracellular virus particles

The period of time between attachment of a virus to its target cell, entry, replication of its genome, production of virus proteins and assembly of virus particles is known as the Eclipse period. The time taken for virus particles to appear extracellularly is known as the Latent period.

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8
Q

What are the characteristics and properties of viruses?

A
  • smallest known infective agent
  • No metabolic activity outside of host cell (eg replication)
  • Mostly highly species specific

The ones that cross between species are the biggest threat

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9
Q

Whats the benefit of a virus having a capsid?

capsid= protein coat and envelope= lipid memebrane

A
  1. Aids in transfer (how naked viruses can bind to cell)
  2. Protects nucleic acids

some viruses have an envelope and some dont-> called naked viruses

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10
Q

What is the genetic content of virsues?

Eg. DNA or RNA? SS or DS? Plasmid? Chromosome?

A
  • DNA or RNA
  • single stranded or double stranded
  • linear or circular
  • or can be one or segmented
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11
Q

What are the different structures of capsids? Give examples of viruses

A
  • Polyhedral/cubodial : Mastadenovirus
  • Helical : Ebola
  • Complex/ Binal : Bacteriophage

binal = have both polyhedral and helical components, head and tail

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12
Q

Where does a virus get its envelope from? Whats it composed of?

A
  • Which ever host cell structure it exited from (eg golgi body, ER, plasma membrane)
  • Phospholipid, protein, glycoprotein spikes
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13
Q

What virus has an envelope?

A
  • Influenza
  • Rabies
  • HIV
  • Herpes
  • All viruses with helical capsids

Polyhedral capsids can be either enveloped or non enveloped

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14
Q

Is it +ve sense or -ve sense thats the coding strand in SS DNA viruses?

A

+ve sense. It acts like mRNA
-ve sense needs to be copied into coding strand first

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15
Q

Give the structure/composition of the following viruses:
1. Adenovirus
2. Herpes
3. Influenza
4. Smallpox

A
  1. Icosohedral, linear DS DNA, non-enveloped
  2. Icosohedral, linear DS DNA, enveloped
  3. Helical (8 segements), -ve RNA, enveloped
  4. Complex, linear DS DNA, enveloped
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16
Q

How are viruses classified?

A

1st by their nucleic acid (DNA or RNA)
2nd by the presence of an envelope
3rd by their symmetry

17
Q

How are viruses classified with Baltimore classification?

A

1-3 like normal, and 4th by their genome architecture (aka how they manipulate their genome to get to mRNA)

I ds DNA
II ss DNA-> ds DNA
III ds RNA
IV +RNA -> -RNA
V -RNA
VI +RNA RT -> -DNA -> ds DNA

RT= reverse transcription, retroviruses use reverse transcription

18
Q

Where are viruses grown? How are they quantified?

A

Grown:
- tissue culture
- chicken egg

Quantified:
- plaque assay: count amount of virus in a sample
- cytopathic method : TCID50= amt of virus to show infection in 50% of cultures
- one step growth curve: for looking at production of virus from cell culture

Plaque assay: usually ten-fold dilution
One step growth curve: tells rate and type of infection
- latent period= period gearing up for infection (making proteins)
- eclipse period= time between infection and appearence of a virus

Microorganisms, Infection, Immunity (26 decks)

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