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Micro/Immuno > Virus Classification, Structure & Replication > Flashcards

Virus Classification, Structure & Replication Flashcards

1
Q

What are the attributes for Virus Classification?

A

1) Virus particle structure
2) Genome
3) Replication Structure
4) Serology
5) Stability

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2
Q

True or false: Every virus has a nucleocapsid

A

True

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3
Q

What is a nucleocapsid?

A

RNA or DNA in a core that is protected by a protein coat (capsid), virus particle structure is defined by nucleocapsid structure

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4
Q

What kinds of nucleocapsid structure are there?

A

Helical, pleomorphic, icosahedral

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5
Q

What are nucleocapsids composed of?

A

repeating protein subunits called capsomeres

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6
Q

What are viral envelopes?

A

virus-modified cellular membranes acquired upon exit from host, exposure to lipid solvents in the lab (alcohol, ether, acetone, Freon etc.) render enveloped viruses noninfectious

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7
Q

True or false: Enveloped viruses may have nucleocapsids with different structures.

A

True

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8
Q

What is the size range of virus particles?

A

Smallest = 18 nm, Largest = 300 nm

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9
Q

What kinds of DNA are in the viral genome?

A

Double stranded & single stranded

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10
Q

What kinds of RNA are in the viral genome?

A

1) Double stranded
2) single stranded
- Plus sense (+) ssRNA - ready to make protein, can sit down on ribosomes and immediately start making viral proteins
- Minus sense (-) ssRNA
- Ambisense

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11
Q

What structures are found in viral genome?

A
  • Linear
  • Circular
  • Segmented
  • Diploid
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12
Q

What is the central dogma?

A

Main flow of things is DNA –> RNA –> Protein

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13
Q

What do most DNA viruses need that RNA viruses don’t?

A

Most DNA viruses need access to nucleus of cell and host replication machinery

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14
Q

What do most RNA viruses need that DNA viruses don’t?

A

Most RNA viruses need RNA dependent RNA polymerase

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15
Q

What are the steps of viral replication?

A

1) Attachment
2) Entry
3) Transcription
4) Translation
5) Replication
6) Assembly
7) Release

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16
Q

How does attachment work?

A

1) Virus receptor binds to cellular receptor - Viruses do not usually mimic cell receptor’s normal ligands (they are a spike like projection on particle surface) They may require a co-receptor
* Genetic engineering can change receptor recognition.

17
Q

What is a major determinant of virus tropism (host range)?

A

attachment

18
Q

True or false: Viruses infect essentially all known life forms

A

True

19
Q

What is a major factor in virus eradication?

A

host range (Small pox = humans only vs. Yellow fever = humans and mosquitoes)

20
Q

How does entry work?

A

1) Receptor mediated endocytosis, or,
2) Direct penetration of plasma membrane

*Non-enveloped viruses not well understood - pores, and membrane disruption

21
Q

How does entry work for enveloped viruses?

A

1) membrane fusion (influenza), HA protein exposed to pH drop = conformational change = allows membrane attachment and fusion
2) Uncoating - Nuclear replication = genome delivered to nucleus, or Cytoplasmic replication = release of genome in cytoplasm then genome is transported to intracellular site of replication (many RNA viruses replicate in membrane associated complexes)

22
Q

True or false: dsRNA viruses always release their genomic material from the entering particle

A

False, they NEVER do

23
Q

How does transcription work?

A

Messenger RNA (mRNA) templates for protein synthesis are produced. DNA viruses rely on cellular RNA polymerases.

The genome of (+) ssRNA viruses can serve as mRNA (production of new transcripts can occur later using a (-) ssRNA template)

(-) ssRNA, dsRNA viruses have to bring their own polymerases into the cell

24
Q

How does translation work?

A

Production of proteins.
All viruses use cellular ribosomes to produce proteins.
Structural proteins are produced in high quantities.

25
Q

True or false: Viral protein production can be regulated at the mRNA (transcript), or translation level.

A

True

26
Q

T or F: Non-structural proteins are seen outside the infected cell.

A

false! only on the inside

27
Q

T or F: Order of events during genome replication depends on virus genome

A

True

28
Q

How does (+) ssRNA genome replication work?

A

1) genome serves as template for translation

2) Polymerase makes (-) ssRNA copy as template for new genomes

29
Q

How does (-) ssRNA genome replication work?

A
  • viral particle must include the viral polymerase
  • polymerase makes mRNA for translation
  • genome replicates through full-length (+) ssRNA intermediate
30
Q

How does dsRNA genome replication work?

A
  • viral particle must include the viral polymerase
  • dsRNA induces innate immune response so genome stays inside particle
  • mRNA synthesized in particle and exported to cytoplasm
  • mRNA serves as (+) strand in virus genome, (-) strand synthesized during assembly
31
Q

How does ssDNA & dsDNA genome replication work?

A
  • Must gain access to the nucleus (except poxviruses, their virons contain the necessary RNA polymerase and the genome encodes the DNA polymerase for replication)
  • Cell is prepared for DNA replication - growth phase, dNTP production, replication machinery
  • Ensure genome ends are copied
32
Q

How does assembly work?

A
  • Packages new genomes into functional particles
  • Localize structural proteins = cellular viral factories
  • Genome contains packaging signals
  • Mechanism
  • Adenovirus - empty protein coat imports genome
  • Reovirus - RNA packaged during capsized assembly
  • Retrovirus - reassembly on membrane
33
Q

How does release work?

A
  • Lysis - viral molecules rupture cellular membrane (bets known for bacteriophage)
  • Weak lysis - depends on membrane breakdown after cell death
  • Budding - (for enveloped only) cell membrane used as outer coat of virus particle
34
Q

How does Viral Kinetics work?

A
  • Infect every cell at the same time (MOI >5)
  • Every cell dies at the end of infection

-Phases on graph:
1) Eclipse = attachment & uptake
2) Exponential growth = replication & assembly
3) Plateau = cell death
The time for one step growth = start of infection to beginning of plateau, for bacteriophage is 30 min, VSV is 6 hours, Vaccina is 24 hours

*Useful to assess mutations, cell entry and process design

35
Q

How are viruses detected and quantified?

A

1) Initial discovery - disease in a host/contaminant in cell culture
2) Confirmation - purification of virus, confirmation of disease

  • Principle Methods:
  • Infectivity
  • Physical
  • Genome
  • Serological

Micro/Immuno (3 decks)

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