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Viruses > Genetic Variation in Viruses > Flashcards

Genetic Variation in Viruses Flashcards

1
Q

What are the 4 types of RNA?

A

double stranded RNA
Single stranded negative sense RNA
Single stranded positive sense RNA
retroviruses

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2
Q

Only this type of viral RNA can be translated to viral protein.

A

single stranded positive sense RNA

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3
Q

What are examples of double stranded DNA viruses?

A

bacteriophage, papovavirus, adenovirus, herpes viruses

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4
Q

DNA-dependent DNA polymerase is used for?

A

replication of DNA

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5
Q

RNA-dependent DNA polymerase is used in what type of viruses?

A

retroviruses

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6
Q

DNA-dependent RNA polymerase is used for?

A

transcription

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7
Q

What is transcription in negative sense RNA viruses and what enzyme is used?

A

negative sense viral RNA is converted to positive sense RNA to be translated to make viral proteins

RNA-dependent RNA polymerase

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8
Q

What are examples of negative sense viral RNA?

A

orthomyxoviruses (influenza), paramyxoviruses, and rhabdoviruses

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9
Q

Picornaviruses, togaviruses, and coronaviruses are what kind of RNA viruses?

A

positive sense RNA

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10
Q

What is the advantage of positive sense RNA viruses over negative sense RNA viruses?

A

they can replicate and produce viral proteins much faster as they are already positive sense AKA mRNA that is ready to be transcribed

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11
Q

Picornaviruses, togaviruses, coronaviruses, and retroviruses are what kind of RNA viruses?

A

positive sense RNA

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12
Q

What is the only type of viruses can make DNA from RNA?

A

retroviruses

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13
Q

What is the only type of viruses can make DNA from RNA? What is this process called? what are examples of viruses that do this?

A

retroviruses

Reverse transcription

HIV-1, HTLV-1

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14
Q

We cannot integrate RNA into our genome. We can only integrate what type of genome into our genome?

A

double stranded DNA

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15
Q

Which viruses, DNA or RNA are more easily mutated and why?

A

RNA viruses are much easier to be mutated than DNA viruses because during replication they use RNA-dependent RNA polymerase which has no proof-reading capabilities. DNA replication uses DNA-dependent DNA polymerase which has proof-reading capabilities.

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16
Q

Humans have 3 types of RNA polymerases which are? What are their respective functions?

A

RNA poly I: rRNA
RNA poly II: mRNA
RNA poly III: tRNA and 5sRNA

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17
Q

For humans, what is the only single stranded viral DNA?

A

Parvovirus: B19

18
Q

In dsDNA only one strand is encoded. In dsRNA both strands can be encoded. This is why RNA viruses are the only ones to engage in this type of recombination.

A

copy-choice recombination where the polymerase switches the template while copying the RNA

19
Q

Retroviruses not only produce DNA but they can also produce RNA. True or false?

A

True

20
Q

Complementation occurs between two or more mutations in __________genes, thus a ____-phenotype occurs. Non-complementation mutations occur in the _______gene.

A

different
WT
same

21
Q

Humans do not have reverse transcriptase. This enzyme is very specific for?

A

retroviruses

22
Q

Retroviruses have what sense of single stranded RNA?

A

positive

23
Q

What causes viral genetic variations?

A

spontaneous genetic variations and mutations that are induced by physical or chemical means

24
Q

Consequences of viral genetic variations can result in phenotypic changes such as?

A

-conditional lethal mutants
 e.g. temperature sensitive (ts) mutants that will grow at low temperature e.g. 31 degrees C but not at e.g. 39 degrees C, wild type grows at 31 and 39 degrees C.

  • Plaque size
 that may be larger or smaller than in the wild type virus
  • Drug resistance
: development of antiviral agents
  • “Hot” mutants
These grow better at elevated temperatures than the wild type virus.
  • Attenuated mutants
Many viral mutants cause much milder symptoms (or no symptoms) compared to the parental virus
  • Enzyme-deficient mutants
Some viral enzymes are not always essential and so we can isolate viable enzyme-deficient mutants; e.g. herpes simplex virus TK
25
Q

Hepatitis B virus can only infect liver cells. What does this say about the specificity of the viral interaction with cells?

A

viral interaction with cells are very specific!!

You can never use HMCV to infect mouse and you cannot use mouse MCV to infect humans.
Zika virus on the other hand can infect humans, monkey, and mosquitoes (this is how viruses can circulate from animals and humans).

26
Q

What is a viral plaque?

A

A viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium. The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques. Counting the number of plaques can be used as a method of virus quantification.

27
Q

HIV patients have to take drug for LIFE because of what resultant phenotype due to viral mutations?

A

drug resistance

HIV patients have to take medications for LIFE or they will have AIDS because of drug resistance of the virus.

28
Q

What is a mutation in virus?

A

if it occurs in the coding sequence, the mu

29
Q

What is a mutation in virus?

A

if it occurs in the coding sequence (the open reading frame), the mutation consequence can be silent, missense or nonsense

30
Q

What is a selection in virus?

A

if you put the virus into very specific conditions, only part of the virus can grow and that virus is selected

a condition-driven variation, causing a conditional grow of the mutant

31
Q

What is complementation in viruses?

A

it occurs when two different viruses infect one cell; if they both have different mutations they can complement each other

occurs between two or more different mutations

32
Q

What is recombination in viruses?

A

mostly happen when exists homologous DNA or RNA sequences between two unrelated DNAs or RNAs

33
Q

What is reassortment in viruses?

A

very important for the influenza virus; if the viral genome has more than one segment this occurs very often

rearrangement of segments genome between two or more viruses

34
Q

If you add or delete 3, 6, or 9 base pairs you will not have an ORF shift. If you add or delete 1 or 2 you have an ORF shift. True or false?

A

True

each amino acids is encoded by 3 bases called a codon

35
Q

What is the difference between silent, missense, and nonsense mutation?

A
  • silent: the mutation has no effect on the gene products
  • missense: usually point mutation, the amino acid will be changed
  • -nonsense: causing big truncation or premature stop codon or OFR (open reading frame) shift
36
Q

When you reculture viruses in some certain condition, for example under temperature changes. Some viruses will not survive but others will. The ones that survive will be selected and recultured to produce new generation which will again be selected upon for viable progeny. This is?

A

selection

37
Q

CRISPR-Cas9 was adapted from a naturally occurring genome editing system in bacteria. Break and rejoin system AKA what only occurs in DNA or RNAs that produce DNA such as retroviruses?

A

recombination

Exchange of genetic information between 2 genomes, classic recombination involves breaking of covalent bonds within nucleic acid, exchange of genetic information, and reforming of covalent bonds

  1. This kind of break/join recombination is common in DNA viruses or the RNA
    viruses which have a DNA phase (retroviruses). The host has recombination
    system for DNA.
  2. Recombination of this kind is rare in RNA viruses.
  3. “Copy choice” kind of mechanism: polymerase switches the templates while
    copying the RNA
  4. So far, there is no evidence for recombination in the negative stranded RNA
    viruses to cause viable viruses
38
Q

Reassortment occurs in viruses that have more than one segment. What are examples of such viruses?

A

Orthomyxovirus: Influenza virus
Retrovirus: HIV, HTLV
Arenavirus: lymphocytic choriomeningitis virus
Bunyavirus: California encephalitis virus, hantavirus
Reovirus: rotavirus

39
Q

Influenza virus and HIV have how many segments respectively?

A

Influenza virus: 8 segments

HIV: 2 segments

40
Q

What is the difference between genotype and phenotype?

A

Genotype: refers to actual genetic change from wild-type in a particular DNA or RNA sequence;

Phenotype: refers to the manifestation of the genotype (phenotype = the observed properties of an organism)

One genotype can have more than one phenotype.

41
Q

What is the differences between viruses and other organisms?

A

Genetic materials: RNA, ssDNA, or dsDNA

Dependent on host

Viruses grow rapidly –> large number of progeny virions per cell –> more chances of mutations over a short time.

42
Q

Reassortment can only occur between influenza viruses of the same type. So influenza A cannot exchange genetic material with influenza B or C.

A

This is not fully understood.

Viruses (8 decks)

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