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Microbio Midterm II > Lecture 12: Taxonomy of Viruses > Flashcards

Lecture 12: Taxonomy of Viruses Flashcards

1
Q

How are viruses classified?

A

Based on characteristics

Ie Nature of host, type of disease caused, life cycle, type of nucleic acid and strandedness

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2
Q

What is the baltimore classification scheme?

A

Classification based on type of genome

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3
Q

What are class I viruses?

A

dsDNA (lambda, T4, herpes, pox)

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4
Q

What are class II viruses?

A

ssDNA (phiX174)

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5
Q

What are class III viruses?

A

dsRNA

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6
Q

What are class IV viruses?

A

ssRNA (+)

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7
Q

What are class V viruses?

A

ssRNA (-)

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8
Q

What are class VI viruses?

A

ssRNA (Replicates with DNA intermediate)

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9
Q

What are class VII viruses?

A

dsDNA (replicated with RNA intermediate)

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10
Q

What does + configuration mean? (RNA)

A

Same strand as mRNA, translated directly

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11
Q

What does - configuration mean? (RNA)

A

Complementary to mRNA, needs to be transcribed into + strand before translation

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12
Q

What are the 5 steps of the viral life cycle?

A
  1. Attachment
  2. Penetration
  3. Replication of nucleic acid, transcription and protein synthesis
  4. Maturation
  5. Release
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13
Q

What occurs in the penetration stage of the viral life cycle?

A

Virus genome enters cell
Naked viruses: complete virion may enter cell
Enveloped viruses: may leave envelope @ cell surface, only nucleocapsid enters cell, or whole virus enters cell

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14
Q

What occurs in the maturation stage of the viral life cycle?

A

Assembly of virus components.

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15
Q

What is the latent period in the viral life cycle?

A

Replicating, making new proteins (eclipse)

Maturation-time needed for component assembly

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16
Q

What is the rise period of the viral life cycle?

A

Virions detected outside of cell, lysis

can also bud out if virus is enveloped

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17
Q

What is viropexis?

A

process whereby certain viruses become attached to a cell wall and are incorporated into the cell by endocytosis

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18
Q

What is burst size?

A

of virions released through lysis

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19
Q

What are the 2 types of bacteriophages?

A

Virulent and temperate

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20
Q

How does T4 infect bacteria?

A
  1. T4 attaches to core region of LPS by tail fibres
  2. Tail sheath contracts, forces central core through outer membrane
  3. Tail lysozymes digest peptidoglycan
  4. DNA enters cytoplasm
21
Q

How does T4 replicate?

A

Nucleases and DNA pol and new sigma factors=new phage DNA

Self assembly=mature phage

22
Q

What kind of phage is lambda?

A

Temperate phage

23
Q

What kind of phage is lambda?

A

Temperate phage, phage carried on chromosome. Contains linear dsDNA with cohesive ends.

24
Q

What is a prophage?

A

Phage genome within host cell membrane

25
Q

What is a lysogen?

A

Bacterium that contains prophage

26
Q

What are cohesive ends?

A

Single stranded dsDNA, allows it to form into circular DNA (complementary bps)

27
Q

Where is the lamdba genome integrated on the bacterial chromosome?

A

attlambda site. Lambda integrase catalyzes integration of phage genome at this site.

28
Q

What kind of phage is phix174?

A

+ strand phage , ssDNA

29
Q

How does phix174 replicate?

A
  1. replicative form (- strand formed to make dsDNA) made, replication via rolling cycle
  2. replicative form of DNA nicked by Gene A protein
  3. New + strand begins synthesis
30
Q

What kind of phage is MS2?

A

ssRNA, + strand

31
Q

How does MS2 infect bacteria?

A

Genome is first used as mRNA, directs synthesis of RNA replicase (RNA dependant RNA polymerase:host doesn’t have)
RNA replicase synthesizes - strand RNA->used to provide additional mRNA and genome

32
Q

Where are the genome of DNA viruses replicated?

A

Nucleus

33
Q

Where are the genome of RNA viruses replicated?

A

Cytoplasm

34
Q

What kind of viruses are Herpes and HPV?

A

DNA viruses

35
Q

How do herpes and HPV infect cells?

A

Viropexis, nucleocapsid transported to nucleus=viral DNA uncoated
Assembly occurs in nucleus, envelope added via budding through inner membrane of nucleus

36
Q

What kind of viruses are polio and hep A?

A

+ strand ssRNA

37
Q

What kind of viruses are measles, rabies and influenza?

A
  • strand ssRNA
38
Q

What kind of viruses use dsRNA?

A

Rotavirous (Reovirus)

39
Q

What is a retrovirus?

A

Virion carries 2 identical copies of genome, reverse transcriptase, integrase, and proteases
DNA Genome travels to nucleus and is integrated into host DNA

40
Q

What are LTR’s?

A

Long terminal repeats: Contain promoters for transcription & participate in integration.

41
Q

What is a provirus?

A

Integrated Viral DNA. cannot be excised from host

42
Q

What does reverse transcriptase do?

A

Transcribes RNA to DNA

43
Q

Which viruses use RNA dependent RNA polymerase?

A

dsRNA and -ssRNA

44
Q

What is a heterokaryon?

A

multinucleate cell that contains genetically different nuclei

45
Q

What is cell fusion?

A

Two cells are brought together by a virus and fuse.

46
Q

What are the 4 ways a viral infection can turn normal cells into tumor cells?

A
  1. Transduction
  2. Insertion of strong promoter
  3. Inactivation of tumor supressor gene
  4. Expression of a viral protein that induces transformation
47
Q

What is transduction? (RNA virus)

A
  1. Virus take oncogene from host and places oncogene into its own genome
  2. Virus places this oncogene into healthy cell=tumor
48
Q

Describe the mechanism of inserting a promotor. (Retrovirus)

A

(No oncogenes encoded)

  1. Insertion of a strong promoter of provirus next to protooncogene
  2. oncogene is expressed at high levels

Microbio Midterm II (7 decks)

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