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2) Introductory Microbiology COPY > Taxonomy of Viruses > Flashcards

Taxonomy of Viruses Flashcards

1
Q

What do virus families end in?

A

-viridae

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2
Q

What do virus genus names end in?

A

-virus

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3
Q

What are the characteristics that influence the classification of virus taxonomy?

A
  • Nature of the host (animal, plant, bacteria)
  • Type of disease caused
  • Life cycle
  • Naked or enveloped
  • Type of nucleic acid and strandedness
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4
Q

What is the classification based on in the Baltimore Scheme?

A

Based on the type of genome

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5
Q

What are the two types of RNA genomes?

A
  • Plus

- Minus

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6
Q

What is a Plus RNA genome?

A
  • Same strand as mRNA

- Can be translated directly

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7
Q

What is a Minus RNA genome?

A
  • Complementary to mRNA

- Needs to be transcribed into + strand before it is translated

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8
Q

What are the 6 steps to the life cycles of viruses?

A

1) Adsorption
2) Penetration
3) Uncoating
4) Replication
5) Maturation
6) Release

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9
Q

What is adsorption?

A

Attachment of the virus to specific receptors on the surface of the cell

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10
Q

How are plant viruses usually introduced into the host?

A

By insect vectors, or following mechanical damage

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11
Q

What is penetration?

A

Virus genome enters the cell

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12
Q

How do enveloped and naked viruses penetrate the cell?

A

Complete virion may enter the cell

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13
Q

How do enveloped viruses penetrate the cell?

A

Envelope may be left at the cell surface, such that only the nucleocapsid enters the cell

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14
Q

How do naked viruses penetrate the cell?

A

Nucleocapsid may be left at the surface

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15
Q

What is uncoating?

A

Removal of the envelope and/or the nucleocapsid by host enzymes, sometimes within lysosomes (in Eukaryotes)

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16
Q

What is replication?

A

Replication of the nucleic acid, transcription, and protein synthesis

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17
Q

What is maturation?

A

Assembly of virus components, nucleic acid, nucleocapsid, and accessory proteins to form new virions (usually spontaneous)

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18
Q

What is release?

A

Mature virions exit the host cell by means of budding or by causing lysis of the cell

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19
Q

How do plant viruses exit?

A

Exit and are transmitted by means of vectors

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20
Q

What kind of virus undergoes direct penetration?

A

Naked viruses

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21
Q

What kind of virus undergoes membrane fusion?

A

Enveloped viruses

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22
Q

What kind of virus undergoes endocytosis? What is thsi called?

A
  • Most enveloped viruses

- Viropexis

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23
Q

What is viropexis? What does it result in?

A
  • Viruses are delivered to lysosomes, which degrade the nucleocapsid and the nucleic acid is released into the cytoplasm
  • Virion has two membranes: one from the virus, and the other from the cytoplasmic membrane of the cell
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24
Q

What are the two major periods of virus replication?

A
  • Latent Period

- Rise Period

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25
Q

What is the latent period composed of?

A

Eclipse and maturation

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26
Q

What is eclipse?

A

Time necessary for the host cells to replicate the viral genome and to synthesize the viral components

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27
Q

What is maturation?

A

Time needed for the different components to be assembled

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28
Q

What is the release/rise period?

A
  • When virions are detected outside of the cell
  • Lysis
  • Budding
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29
Q

Is lysis or budding faster?

A

Lysis is faster

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30
Q

What causes cell lysis?

A
  • Virus-encoded proteins damage the cytoplasmic membrane

- In bacteria, they destroy the peptidoglycan layer

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31
Q

What kind of viruses use budding?

A

Enveloped viruses

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32
Q

What is release by budding?

A
  • When viruses steal and coat themselves with a piece of the membrane of the host cell (cytoplasmic or organelle membrane)
  • The host is not affected by the process, but they will release virions over a longer period of time
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33
Q

The best-studied bacteriophages infect _______

A

E. coli (Gram-Negative)

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34
Q

Most bacteriophages contain (linear/circular) (ss/ds) (RNA/DNA) genomes.

A

linear dsDNA

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35
Q

Are most bacteriophages naked or enveloped?

A

Most are naked, but some possess lipid envelopes

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36
Q

What are the two types of bacteriophages?

A
  • Virulent phages (lytic pathway)

- Temperate phages (lysogenic pathway)

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37
Q

What are virulent phages? Give an example.

A
  • Replication results in host cell lysis (lytic pathway)

- T4

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38
Q

What are temperate phages?

A
  • The genome becomes incorporated into the bacterial host genome (lysogenic pathway)
  • Lambda
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39
Q

How does bacteriophage T4 undergo adsorption?

A

T4 attaches to the core region of LPS by the tail fibers

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40
Q

What happens after adsorption in bacteriophage T4?

A
  • Tail sheath contracts, forcing the central core through the outer membrane
  • Tail lysozymes digest the peptidoglycan layer, forming a small pore
  • Phage DNA is then injected into the cytoplasm of the host cell
  • Genome is copied, the phage is assembled, and the cell will lyse, causing the virions to be liberated outside of the cell
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41
Q

What does infection by temperate phages result in?

A

Results in a prolonged, latent state of infection

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42
Q

Where is the phage carried in temperate phages?

A

On the chromosome

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43
Q

What is a prophage?

A

Phage genome WITHIN the host cell chromosome

44
Q

What is a lysogen?

A

Bacterium that contains the prophage

45
Q

What is excision in temperate bacteriophage?

A

When the prophage exists the chromosome

46
Q

What can happen after excision in temperate bacteriophage? When would this happen?

A
  • It can continue along the lytic pathway through induction, resulting in the production of new virus particles and host cell lysis
  • If conditions are bad
  • Results in 100 billion new virions instead of 10
47
Q

Can the prophage replicate?

A

Yes, and its descendants will also carry the viral genome

48
Q

What are the characteristics of phage lambda’s genome?

A
  • Linear dsDNA with cohesive ends, a region of single-stranded complimentary DNA
  • The cohesive ends join, forming a circular molecule of dsDNA
49
Q

Where is the Lambda genome integrated in the bacterial chromosome?

A

At the att(lambda) site

50
Q

The _____ region in the phage genome is homologous to the _____ site

A 
att
att(lambda)
51
Q

Which enzyme catalyzes the integration of the genome at att(lambda)?

A

Lambda integrase

52
Q

What kind of bacteria can get infected to a bacteriophage?

A

Any bacteria that has a homologous DNA to the bacteriophage can get infected

53
Q

How does ssDNA phage replicate?

A

1) The minus-strand is synthesized to produce a dsDNA genome
2) mRNA can form the minus strand, and ssDNA can be replicated by rolling circle
3) Results in a new plus-strand ssDNA

54
Q

What is the rolling circle mechanism?

A
  • ssDNA replication
  • The + strand is cut, unrolled, which allows a new + strand to be formed
  • Results in a new + ssDNA
55
Q

How does ssRNA phage replicate?

A

1) The virus MUST supply the enzyme RNA replicase
2) RNA replicase uses the minus-strand to make plus-strand copies
3) Assembly

56
Q

Why does ssRNA need the enzyme RNA replicase?

A

Since the host cell does not have the function to replicate

57
Q

Where are the genomes of DNA viruses replicated?

A

In the nucleus

58
Q

Where are the genomes of RNA viruses replicated?

A

In the cytoplasm

59
Q

What is an example of a DNA genome virus?

A

Herpes; replicates in the nucleus

60
Q

How does a DNA genome virus penetrate a cell?

A
  • Fusion of the cell cytoplasmic membrane with the virus envelope
  • Nucleocapsid is transported to the nucleus where viral DNA is uncoated
61
Q

In DNA genome virus, what does the host transcription/translation apparatus synthesize?

A
  • Immediate early proteins (transcription factors and, in some cases, virus-specific RNA polymerase
  • Delayed early proteins (viral-specific DNA polymerase, and other viral proteins necessary for replication)
  • Late proteins: nucleocapsid
62
Q

Where does assembly occur in DNA genome viruses? How?

A
  • In the nucleus
  • Envelope is added via a budding process through the inner membrane of the nucleus
  • The complete virions are then secreted out of the cell by the ER-Golgi pathway
63
Q

Can the ssDNA genome be replicated?

A

No, it is first converted to the dsDNA replicative form

64
Q

What is an example of a plus-strand RNA genome virus? What does it cause?

A
  • Poliovirus (Hepatitis A)
  • Causes poliomyelitis (skeletal deformations, flu-like symptoms)
  • Safe and effective vaccine
65
Q

How do plus-strand RNA genome viruses replicate?

A

The plus-strand RNA serves as a template for the synthesis of a large polyprotein that is cleaved into proteins

66
Q

What are examples of minus-strand RNA genome viruses?

A

Measles (pneumonia, encephalitis, death), rabies, influenza

67
Q

How does the minus-strand RNA genome virus replicate?

A

The minus-strand is first transcribed into a plus-strand RNA by RNA-dependent RNA polymerase carried inside the virions

68
Q

What enzyme is necessary for the replication of minus-stranded RNA genome viruses?

A

RNA-dependent RNA polymerase

69
Q

What is an example of dsRNA genome viruses?

A

Rotavirus

70
Q

How does the dsRNA genome virus replicate?

A
  • The dsRNA genome cannot be transcribed
  • A plus-strand RNA must be synthesized by a viral-encoded RNA-dependent RNA polymerase using the minus-strand as the template
  • The plus-strand is then translated into proteins and is used as a template to synthesize a minus-strand to yield dsRNA genomes
71
Q

What is an example of retrovirus RNA genome viruses?

A

HIV

72
Q

Can you cure HIV?

A
  • No, if there is a piece of DNA of the virus inside your genome, you will have to kill every infected cell to cure HIV
  • You can inhibit the growth with drugs
73
Q

What does the virion of retrovirus RNA genome carry?

A

Two identical copies of the genome (plus-strand ssRNA), reverse transcriptase, integrase, and proteases

74
Q

What is the reverse transcriptase in retrovirus RNA genome viruses? What is its function?

A

RNA-dependent DNA polymerase that reverse transcribes the RNA genome in to DNA

75
Q

Once DNA polymerase has transcribed RNA into DNA in retroviruses, where does it travel?

A

DNA genome travels to the nucleus and is integrated into the host DNA

76
Q

What happens to the retrovirus once it is integrated into the host DNA? How do the virions escape?

A
  • Transcription into mRNA and ssRNA genome, which are imported into the cytoplasm
  • Production of virions, which exit the cell by budding
77
Q

What are LTR?

A
  • Long-terminal repeats

- Contain promoters for transcription and participate in the integration process

78
Q

What are proviruses?

A

Integrated viral DNA

79
Q

How do proviruses defer from prophages?

A

Contrary to the lambda prophage, the provirus cannot excise from the host genome

80
Q

What does cell fusion between enveloped viruses and the cytoplasmic membrane result in?

A

In hybrid cells that have chromosomal aberrations, and are usually short-lived

81
Q

What is an example of an oncogenic virus?

A

Hepatitis-C virus induces liver cancer

82
Q

What is a tumor cell?

A

A cell that has acquired immortality, characterized by its uncontrolled replication

83
Q

Some viral infections are implicated in the conversion of a normal cell into a tumor cell. What is this process called?

A

Transformation

84
Q

Are DNA or RNA viruses known to cause tumors?

A

Both

85
Q

What are the 4 different mechanisms of oncogenic viruses?

A
  • Transduction
  • Insertion of a strong promoter
  • Inactivation of a tumor suppressor gene
  • Expression of a viral protein that induces transformation (DNA virus)
86
Q

What is an example of an oncogenic virus that acts through transduction?

A

Rous Sarcoma RNA Virus (avian virus)

87
Q

What do oncogenic virus that acts through transduction carry?

A

Carries one or many oncogenes (tumor-causing genes) called v-oncogenes

88
Q

Where are v-oncogenes acquired from? What is this process called?

A
  • The host

- Transduction

89
Q

What is SRC in poultry?

A
  • Contained in all normal cells in poultry

- An adapter protein that orchestrates signal transduction

90
Q

What happens when a cell is infected with the Rous Sarcoma virus?

A

Suddenly it acquires additional copies of the SRC gene, which results in transformations of the cell

91
Q

Oncogenes are like normal genes found in Eukaryotes, known as ________ or ________

A

proto-oncogenes or c-oncogenes

92
Q

What is the proto-oncogene involved in?

A

Involved in the regulation of the cell cycle or in safety mechanisms that prevent transformation

93
Q

What is an example of an oncogenic virus that acts through insertion of a promoter?

A

Retrovirus

94
Q

Does the retrovirus encode an oncogene?

A

No

95
Q

How does the retrovirus work when it inserts a promoter?

A

Insertion of a strong promoter of the provirus next to a proto-oncogene

96
Q

What happens when a promoter is inserted next to a proto-oncogene?

A
  • The proto-oncogene is then expressed at high levels and results in misregulation of the pathway that prevents transformation
  • Uncontrolled expression of c-onc
97
Q

What is an example of an oncogenic virus that acts through inactivation of tumor-suppressor gene?

A

Retrovirus

98
Q

How does the retrovirus work when it inactivates a tumor-suppressor gene?

A
  • Insertion causes the inactivation of the gene and uncontrolled expression of the proto-oncogene, resulting in transformation
  • Disruption of c-onc; abnormal c-onc is produced, and replication control is lost
99
Q

What is an example of an oncogenic virus that acts through expression of viral protein?

A

DNA virus (Human Papilloma Virus)

100
Q

What do DNA viruses NEED to infect?

A

Actively replicating cells because they only replicate DNA

101
Q

What does HPV infect? What does it lead to?

A
  • Basal cells in the epithelium
  • Cells are replicating very quickly, but are never killed because the genome of the virus is defective
  • Leads to cervical cancer
102
Q

Where does the HPV virus attack?

A

Between the cervix and the genital tract epithelium, viruses can easily reach basal cells

103
Q

Does the HPV viral protein have a cell counterpart?

A

No

104
Q

In oncogenic viruses that act through expression of a viral protein, does the integration of the viral genome into the host genome occur?

A
  • May occur
  • Adenovirus (dsDNA)
  • Or, the viral genome may persist in the cell as extrachromosomal episome
105
Q

How do DNA viruses cause tumors by infecting a non-permissive host?

A
  • They cannot complete their infection cycle
  • The cell is infected an undergoes uncontrolled replication
  • Because the virus cannot complete its replication, the cells will die

2) Introductory Microbiology COPY (24 decks)

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