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Virology > Viral genetics > Flashcards

Viral genetics Flashcards

1
Q

What does it mean by groups, types, and isolates of viruses?

A

A viral group will share one of the same specific antigens but they will also have certain types that have their own specific antigen (sero-types).

Each group has their own isolates

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2
Q

What are the 5 steps a virus takes to infect a cell? In order

A
  1. Attachment
  2. Entry
  3. Release of NA into cell (uncoating)
  4. Replication of virus in cell
  5. Releasing virus to infect other cells
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3
Q

Where do DNA viruses replicate in the host cell? RNA?

A

DNA – nucleus

RNA – cytoplasm

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4
Q

What are the two ways a virus is released from the host cell to infect others?

A

Lysis – cytopathic

Budding – non cytopathic

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5
Q

What does an error in replication lead to?

A

quasispecies

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6
Q

What are quasispecies?

A

Mixture of variant viruses caused by mutation/error in replication

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7
Q

Do DNA or RNA viruses have high spontaneous mutation rates? Why?

A

RNA

RNA-dependent RNA polymerase lacks proofreading capability

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8
Q

What is a mutation?

A

Change in nucleic acid

change in heritable characteristics

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9
Q

What are the 2 major mutations? Explain them

A

Spontaneous - absence of any known mutagen.

Induced - derived from mutagen-treated population of wild type.

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10
Q

What are some mutagens that can cause induced mutations?

A
  1. Nitrous acid
  2. Hydroxylamine
  3. Nitrosoguanidine
  4. 5-bromodeoxyuridine
  5. UV light
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11
Q

T/F

The larger genome size, the higher mutation rate

A

False
The smaller the genome size, the higher mutation rate
virus &laquo_space;bacteria – virus has higher mutation rate

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12
Q

What mutagen causes deamination of adenine to form hypoxanthine which then pairs with cytosine?

A

Nitrous acid (daminates bases)

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13
Q

What are 5 different types of mutations that can happen?

A
  1. Plaque morphology
  2. Host range
  3. Temperature sensitive
  4. Deletion
  5. Point
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14
Q

What change would cause a plaque morphology mutation?

A

cytolytic change
metabolic difference
May cause cells to fuse together (i.e. Herpesvirus)

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15
Q

What are host range mutations?

A

Limited host range changes/expands (one that could only affect horses, now affects dog)

Mutants fail to grow in certain animal or cell line in which the wild-type virus does grow

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16
Q

How can host range mutations be beneficial?

A

We can use some of them for vaccines

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17
Q

what type of mutation is a syncytial mutation synonymous with?

A

Plaque morphology mutation

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18
Q

What are temperature sensitive mutations?

A

Alteration in nucleotide sequence of a gene –> resulting protein product unable to assume its functional configuration at the nonpermissive temperature (39)
Able to assume fnx configuration at permissive temperature (32)

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19
Q

What benefit can come from temperature sensitive mutations?

A

vaccine production

can’t grow in the body

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20
Q

Explain a deletion mutation.

A

Gene is deleted from genome

21
Q

Describe a point mutation

A

Alteration of a single nucleotide in the viral genome.

22
Q

What mutations can be induced in a laboratory setting?

A

Deletion mutations

Point mutations –>Achieved by an in vitro mutagenesis technique

23
Q

What are 2 major genetic interaction b/w viruses?

A

Complementation

Recombination

24
Q

What are the 3 forms of recombination?

A
  1. Breakage-reunion mechanism
  2. Copy-choice mechanism
  3. Reassortment
25
Q

What is complementation?

A

With mixed infected cells – interaction of viral gene products –> increase in yield of one or both parental mutants –> genotypes remain unchanged!!

When two viruses can complement each other. If both have defective gene –> no complementation!

26
Q

why does recombination take place? What are the factors to decide what type of recombination takes place?

A

Due to physical interaction of viral genomes in mixedly infected cells

Factors = type and organization of viral genome

27
Q

Describe breakage-reunion recombination

A

Breakage and reformation of covalent bonds within the NA

28
Q

What type of viruses undergo breakage-reunion recombination?

A

All DNA and RNA viruses that replicate via DNA intermediates

29
Q

Explain copy choice recombination. What type of virus is this most common in.

A

In mixed infection, polymerase switches template strand during RNA sythesis
Ex: two viruses –> shift in template strand and produces two new genomes –> two new viruses

Most likely with ssRNA

30
Q

How does reassortment recombination happen?

A

Genome segments are randomly reassorted in the progeny

31
Q

What type of virus undergoes reassortment recombination?

A

In mixedly infected cells w/ viruses having segmented genomes.

32
Q

T/F

All viral genomes are diploid

A

False

All except retroviruses (2 copies of their RNA) are haploid

33
Q

What is heterozygosis? In what type of infection may this occur?

A

haploid genomes arise due to aberrant packaging of > 1 copy of the genome at maturation –> multipoid particles

Mixed infections

34
Q

What 3 types of non-genetic interaction occurs between viruses?

A
  1. Heterozygosis
  2. Interference
  3. Phenotypic mixing
35
Q

What is phenotypic mixing?

A

Individual progeny of a mixed infection contain structural protein (capsid or envelope) derived from both parents

36
Q

What is pseudotype formation?

A

A progeny genome belongs to one parent while the capsid or envelope is from the other parent

37
Q

What type of infection is seen with interference?

A

Homologous viruses or closely related viruses

Common in viruses that have been serially passaged at high m.o.i.

38
Q

What happens with interference?

A

total yield of virus particles stay the same –> yield of infectious virus drops with increasing passage

large proportion of viral genome contain deletions
–> interference with growth of infectious portion of virus population –> gives rise to increase proportion of defective interfering (DI) virus.

39
Q

What mutation do you get an increasing proportion of defective interfering (DI) virus

A

Interference

40
Q

What are four interactions that happen between virus and host cell?

A
  1. Cell lysis
  2. Transformation
  3. Integration
  4. Persistent infection
41
Q

What causes cell lysis?

A

generation of a large # of virus particles and virus associated proteins of NA

42
Q

What types of viruses tent to transform cells? Why would they do this?

A

DNA viruses
When the cell is not competent to support a full replicative cycle of the virus.

ability to generate tumors when injected into suitable animal host

43
Q

What is integration?

A

genomes of transforming viruses found integrated into genome of the transformed cell

44
Q

How do retroviruses integrate?

A

Using their reverse transcriptase

45
Q

Describe what happens during persistant infection

A

virus must change to no longer kill the cell OR the cell must change to support the virus replication w/o being killed

46
Q

What are two ways of mapping viral genomes?

A
  1. Restriction maps

2. Transcriptional maps

47
Q

What are restriction maps?

A

Physical map of genome of DNA viruses
Started with introduction of restriction endonucleases –> cleaves DNA –> cleavage site provides reference points on genome whose distance from each other are known

48
Q

What do restriction endonucleases do? What process are they used in?

A

Cleave DNA at specific nucleotide sequence

Restriction maps

49
Q

What are transcriptional maps?

A

maps localizing the genomic sequences encoding specific mRNA.

Virology (15 decks)

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