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Virology > Lecture 6 2/6/24 > Flashcards

Lecture 6 2/6/24 Flashcards

1
Q

What is virus evolution?

A

-genomic changes in hereditary genomes that may result in phenotypic changes
-occurs within a viral population

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2
Q

Why is it important for mutation rate to be balanced?

A

-too high of a rate results in defective progeny
-too low of a rate does not allow progeny to adapt to changing environment

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3
Q

Why do RNA viruses tend to have more mutations than DNA viruses?

A

-higher error rates and lower stability
-viral polymerases lack proof-reading mechanisms

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4
Q

What are “hot spots”?

A

certain positions in viral genomes that have higher mutation rates

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5
Q

What are the characteristics of selection pressure?

A

-does not cause mutations
-selects for already existing mutants

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6
Q

What is a mutation?

A

change in the base sequence of a nucleic acid resulting in the alteration of the resulting protein

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7
Q

What happens when mutations occur in less tolerant proteins?

A

results in a non-infectious virus

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8
Q

What are the three types of drift/point mutations?

A

-silent
-substitution
-nonsense

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9
Q

What is a silent mutation?

A

mutation within a codon that produces the same viral protein sequence

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10
Q

What is a substitution mutation?

A

mutation within a codon that produces a different viral protein sequence

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11
Q

What is a nonsense mutation?

A

mutation within a codon that leads to the cessation of the viral protein sequence

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12
Q

What is a conservative substitution?

A

when a different amino acid is substituted, but it has similar properties to the original amino acid

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13
Q

What is a non-conservative substitution?

A

when a different amino acid is substituted that does not have similar properties to the original amino acid

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14
Q

What is a deletion mutation?

A

-deletion of nucleotides
-causes a frameshift mutation
-changes amino acid sequence downstream of mutation

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15
Q

What is an insertion mutation?

A

insertion of multiples of 3nt bases to a viral gene, resulting in the addition of amino acids

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16
Q

Which type of mutation is easy to revert back to wildtype?

A

point mutations

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17
Q

What is reassortment?

A

gene segments are mixed and matched when two different viruses strains end up in same host cell

18
Q

What is recombination?

A

portions of gene segments are interchanged when two different virus strains are in the same host cell

19
Q

What is antigenic drift?

A

-accumulation of small point mutations
-leads to minor antigenic changes with epidemic/seasonal potential

20
Q

What is antigenic shift?

A

-viral reassortment of gene segments
-leads to major antigenic changes with pandemic potential

21
Q

What are the characteristics of canine-parvovirus-2 evolving from feline panleukopenia virus?

A

-only 5 amino acid differences between the structural proteins
-these mutations provided CPV-2 with the ability to bind to the canine transferring receptor and infect dogs

22
Q

What are the characteristics of feline enteric coronavirus and FIP?

A

-FECV is ubiquitous and causes mild enteric disease
-FIPV, a mutation of FECV, occurs in 10% of FECV cases and causes fatal systemic disease
-FIPV cannot be transmitted to other cats, but FIPV-infected cats can shed FECV
-FIPV is likely a mutant that undergoes autonomous infection

23
Q

During which period of gestation can BVDV lead to a persistently infected fetus?

A

50-125 days of gestation

24
Q

How does recombination play a role in BVDV?

A

-PI calves typically have non-cytopathic BVDV strains
-exposure of the PI calf to a cytopathic BVDV strain can lead to recombination between the two strains
-viral genome recombines with host mRNA, leading to expression of proteins that can be toxic

25
Q

What is cancer?

A

when a cell becomes biologically abnormal due to a disruption in cellular transformation and growth

26
Q

How do viruses subvert the cell cycle to their advantage?

A

-target specific steps in cycle to improve viral replication
-induce a G1-S phase transition to replicate their genome during cellular DNA synthesis
-induce a G2/M arrest to provide optimized environment for maximum viral replication levels

27
Q

Which types of mutations from oncogenic viruses can cause cancer?

A

-gain of function mutations in proto-oncogenes
-loss of function mutations in tumor-suppressor genes

28
Q

Which RNA tumor viruses are most important in vet med?

A

retroviruses

29
Q

Which DNA tumor viruses are most important in vet med?

A

herpes and papilloma viruses

30
Q

What are the three standard genes in a model retrovirus?

A

-Gag: structural proteins
-Pol: reverse transcriptase
-Env: envelope protein

31
Q

What are the three main classes of transforming retroviruses?

A

-acute transducing viruses
-non-transducing viruses - chronic
-non-transducing viruses - long latency

32
Q

What is an example of acutely transducing retroviruses?

A

feline sarcoma virus

33
Q

What are the characteristics of acutely transducing retroviruses?

A

-highly oncogenic
-genome contains viral oncogene in place of one of the core genes
-oncogene is replication deficient and requires a helper retrovirus to provide missing core gene
-oncogene expression is controlled by the virus
-oncogenes originate via transduction of cellular proto-oncogenes when they insert proviral DNA during replication

34
Q

What is an example of chronic non-transducing retroviruses?

A

feline leukemia virus

35
Q

What are the characteristics of chronic non-transducing retroviruses?

A

-RNA genome of virus is reverse transcribed into DNA and integrated into host genome (provirus)
-when provirus integrates near a host cell’s oncogene, it can inappropriately activate the gene and cause transformation into cancer
-integration occurs at random spots

36
Q

What is an example of long-latent non-transducing retroviruses?

A

bovine leukemia virus

37
Q

What are the characteristics of long-latent non-transducing retroviruses?

A

-retroviral protein is responsible for cell transformation
-proteins do not appear to affect retroviral replication life cycle
-retroviral protein likely causes uncontrolled transcription of a host cell’s genes

38
Q

What are the characteristics of DNA virus transformation?

A

-genes from DNA virus responsible for transformation are viral in origin
-transforming proteins interact with proto-oncogenes or inactivate tumor suppressors to induce transformation

39
Q

What are the characteristics of Marek’s disease virus?

A

-transforms T cells into other cell types when undergoing latency, leading to uncontrolled proliferation
-disease is contagious
-preventable by vaccination

40
Q

What are the characteristics of papillomaviridae and cancer?

A

-viruses cause benign, superficial tumors
-warts generally regress with age
-in some cases, warts can progress to malignancy
-UV light thought to act as a co-carcinogen
-autologous vaccines possible

Virology (22 decks)

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