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MIMM 324 > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What information is encoded in a viral genome?

A

Replication of viral genome
Assembly and packaging of the genome
Regulation and timing of the replication cycle
Modulation of host défenses
Spread to other cells

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2
Q

All viral genomes must make ____ that can be read by host ribosomes.

A

mRNA

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3
Q

Is mRNA + or - polarity

A

+

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4
Q

What is the + strand?

A

DNA or RNA that is the coding strand (starts with AUG)

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5
Q

What is the - strand?

A

DNA or RNA that is the template strand. Does not contain open reading frame

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6
Q

True or false: All +RNAs are mRNAs

A

False. Ex: Genomic RNA vs sub-genomic mRNAs

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7
Q

What are the seven Baltimore classes?

A
  1. ds DNA
    • ssDNA
  3. ds RNA
    • ssRNA
    • ssRNA
    • ss RNA reverse transcriptase
  7. ds DNA reverse transcriptase
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8
Q

Describe Baltimore Class I viruses

A

Transcribe dsDNA to +mRNA

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9
Q

What are two Baltimore class I viruses whose genomes are copied by host DNA polymerases?

A

Polyomaviridae, Papillomaviridae

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10
Q

What are two Baltimore Class I viruses that encode their own DNA polymerase?

A

Adenoviridae
Poxviridae (replicates in cytoplasm, therefore needs to create its own DNA pol)

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11
Q

Describe Baltimore Class II viruses

A

Convert - or + ssDNA to dsDNA and then transcribes to mRNA

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12
Q

True or false: Baltimore class II viruses can be circular or linear

A

True

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13
Q

Which Baltimore class viruses use an RdRp?

A

dsRNA, + RNA and - RNA

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14
Q

What is RdRp?

A

RNA-dependent RNA polymerase
To make mRNAs and RNA genomes from RNA templates

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15
Q

Which Baltimore class viruses use reverse transcriptase

A

ssRNA-RT and dsDNA-RT

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16
Q

Describe Baltimore Class III viruses

A

dsRNA converted to mRNA by RdRp

17
Q

Describe Baltimore Class IV viruses

A

mRNA can be directly translated

18
Q

Describe Baltimore Class V viruses

A

-RNA gets converted to +RNA through RdRP
Can be segmented or non-segmented

19
Q

Describe Baltimore Class VI viruses

A

+RNA gets converted - ssDNA by reverse transcriptase and then to dsDNA

20
Q

Describe Baltimore Class VII viruses

A

Gapped dsDNA converted to full dsDNA and then transcribed to mRNA

Uses reverse transcriptase when turning +RNA to dsDNA (replicating genome)

21
Q

What is reassortment?

A

Multiple viruses co-infect the same cell
Leads to rapid evolution

22
Q

How were viral stocks maintained in the 1900s?

A

Continual passage from animal to animal

23
Q

Before cell culture, how were viruses propagated?

A

In embryonated chicken eggs
5-14 days after fertilization, hole drilled in shell, the location of viral injection depends on site appropriate for its replication

24
Q

What are the two types of cell cultures?

A

Primary cell cultures
- prepared from animal tissues
- limited life span

Continuous cell lines
- single cell type that can be propagated indefinitely in culture
- HeLa cells: cancer cells
- Tumor tissue or immortalized primary cells
- May not resemble the cell of origin

25
Q

What is evidence of viral growth in culture cells?

A

Rounding up of cells, detachment, cell lysis, syncytial formation (cell fusion), nuclear shrinking/swelling, accumulation of virions/viral proteins, membrane alteration

26
Q

What is the virus titer?

A

Concentration of a virus in a sample

27
Q

What is the plaque assay?

A

Quantitative measure of infectious virus
Count # of infectious viral particles in a suspension

28
Q

How do you calculate the titer in a plaque assay?

A

PFU/volume plated x dilution factor

29
Q

What is a focus-forming unit assay?

A

Modification of the plaque assay for viruses that do not lyse cells

After viral infection, cells are permeabilized and stained with an antibody against a viral protein

30
Q

What is the particle-to-PFU ratio?

A

of physical particles divided by the # of infectious particles

31
Q

Why are viral particles not always successful at infection?

A

Damaged particles, mutations, empty particles, complexity of viral life cycles, antiviral defenses

32
Q

What is MOI

A

Multiplicity of infection
Average number of cells added per cell (not the same as the # of infectious particles each cell receives)

Depends on random collision of virions and cells

33
Q

How do you calculate the fraction of cells infected by one or more viral particles?

A

P(k) = (e^-m) (m^k)/k!
P(k) = fraction of cells infected by k virus particles
m=MOI
e = Euler’s number (approx 2.72)
k! = factorial of k

Fraction of uninflected cells = P(0) = e^-m
Fraction of cells infected with one particle = P(1) = (e^-m)m
Fraction of cells multiply infected = P(>1) = 1-(e^-m)(1+m)

34
Q

How is MOI used in research?

A

Low MOI: experiment requires multiple cycles of infection
High MIO: when every cell in culture needs to be infected
Optimal MOI: optimize number of cells that will be infected with a single viral particle

MIMM 324 (10 decks)

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