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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
What is complementation?
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
why does recombination take place? What are the factors to decide what type of recombination takes place?
Due to physical interaction of viral genomes in mixedly infected cells Factors = type and organization of viral genome
27
Describe breakage-reunion recombination
Breakage and reformation of covalent bonds within the NA
28
What type of viruses undergo breakage-reunion recombination?
All DNA and RNA viruses that replicate via DNA intermediates
29
Explain copy choice recombination. What type of virus is this most common in.
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
How does reassortment recombination happen?
Genome segments are randomly reassorted in the progeny
31
What type of virus undergoes reassortment recombination?
In mixedly infected cells w/ viruses having segmented genomes.
32
T/F | All viral genomes are diploid
False | All except retroviruses (2 copies of their RNA) are haploid
33
What is heterozygosis? In what type of infection may this occur?
haploid genomes arise due to aberrant packaging of > 1 copy of the genome at maturation --> multipoid particles Mixed infections
34
What 3 types of non-genetic interaction occurs between viruses?
1. Heterozygosis 2. Interference 3. Phenotypic mixing
35
What is phenotypic mixing?
Individual progeny of a mixed infection contain structural protein (capsid or envelope) derived from both parents
36
What is pseudotype formation?
A progeny genome belongs to one parent while the capsid or envelope is from the other parent
37
What type of infection is seen with interference?
Homologous viruses or closely related viruses | Common in viruses that have been serially passaged at high m.o.i.
38
What happens with interference?
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
What mutation do you get an increasing proportion of defective interfering (DI) virus
Interference
40
What are four interactions that happen between virus and host cell?
1. Cell lysis 2. Transformation 3. Integration 4. Persistent infection
41
What causes cell lysis?
generation of a large # of virus particles and virus associated proteins of NA
42
What types of viruses tent to transform cells? Why would they do this?
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
What is integration?
genomes of transforming viruses found integrated into genome of the transformed cell
44
How do retroviruses integrate?
Using their reverse transcriptase
45
Describe what happens during persistant infection
virus must change to no longer kill the cell OR the cell must change to support the virus replication w/o being killed
46
What are two ways of mapping viral genomes?
1. Restriction maps | 2. Transcriptional maps
47
What are restriction maps?
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
What do restriction endonucleases do? What process are they used in?
Cleave DNA at specific nucleotide sequence | Restriction maps
49
What are transcriptional maps?
maps localizing the genomic sequences encoding specific mRNA.

Virology (15 decks)

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