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Micobiology > Chapter 9: Viruses and Virology > Flashcards

Chapter 9: Viruses and Virology Flashcards

1
Q

What are viruses?

A

Obligate intracellular parasites

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2
Q

In what four activities are viruses involved?

A
  1. Energy
  2. Biosynthesis
  3. Replication of genetic material
  4. Reproduction
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3
Q

What kind of DNA and RNA do DNA viruses have?

A

ssDNA and dsDNA

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4
Q

What kind of DNA and RNA do RNA viruses have?

A

ssRNA and dsRNA

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5
Q

What kind of DNA and RNA do RNA DNA viruses have?

A

ssRNA (Retroviruses)

dsDNA (Hepadnaviruses)

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6
Q

Name 5 different types of viruses.

A
  1. Bacterial viruses
  2. Archaeal viruses
  3. Animal viruses
  4. Plant viruses
  5. Viruses of eukaryotic cells
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7
Q

What is a virion?

A

A complete extracellular virus particle, with nucleic acid surrounded by protein coat and other materials

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8
Q

What is a capsid?

A

Protein coat, surrounds nucleic acid, determines, virus structure

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9
Q

What is a capsomere?

A

Smallest unit seen with an electron microscope, self assembly

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10
Q

What is a nucleocapsid?

A

Nucleic acid + protein

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11
Q

What is the envelope?

A

Lipids layers around nucleocapsid

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12
Q

Describe what a virion looks like?

A

Using the Tobacco mosaic virus, it is helical and naked

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13
Q

Icosahedrel viruses

A
  • 20 triangular faces

- 12 vertices

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14
Q

Naked vs. enveloped

A
  • Most infect animal cells

- Attachment to host cells

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15
Q

Complex viruses

A

Influenza and T4

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16
Q

Describe the Influenza virus.

A

Polymorphic, helical nucleocapsid, buds off cell envelope

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17
Q

Describe the PhiT4 virus.

A

Icosahdrel head, helical tail

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18
Q

Are enzymes in virions metabolically active or inactive?

A

Inactive

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19
Q

Name four examples of enzymes in virions.

A
  1. Lysozymes
  2. Polymerases for replication
  3. Enzymes for transcription of RNA (reverse transcriptase)
  4. Enzymes for release form host (neuraminidase)
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20
Q

What is a method used to quantify viruses?

A

Plaque assay

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21
Q

Describe a plaque assay.

A
  1. Pour mixture onto solidified nutrient agar plate. This mixture contains molten top agar, bacterial cells, and diluted phage suspension.
  2. Let solidify.
  3. Sandwich on top agar and nutrient agar
  4. Incubate
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22
Q

Animal models

A

Virus that has no effect on cell culture, but causes death

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23
Q

LD50

A

Lethal dose for 50% of the population-titer (concentration) of virus that causes half of the animals to die

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24
Q

Describe the viral replication cycle.

A
  1. The virion with the DNA inside attaches (adsorption) to the cell (host)
  2. Penetration (injection) (protein coat remains outside)
  3. Viral DNA enters
  4. Synthesis of nucleic acid and protein
  5. Assembly and packaging
  6. Release of virions (lysis)
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25
What happens during the eclipse stage of the viral growth curve?
Infectious particles cannot be detected
26
Describe the attachment of a virus to a host cell.
- External virus protein interacts within host cell "receptor" - Receptors must be present for infection to occur
27
What are 3 receptor proteins involved in virus attachment?
– ɸTI—iron uptake protein – ɸʎ—maltose uptake protein – HIV—CD4 on helper T cells (recogni7on of MHC an7gens)
28
• Receptors must be present for infec7on to occur
Absence | – Mutation
29
What is penetration?
Entry of viral genome into host cell
30
What is uncoating?
Virus looses outer coat
31
What protein is involved in penetration?
PhiT4
32
What are some host defenses to viruses?
- Limit attachment - RNA mechanisms - RNAi-eukaryotes - CRISPR-prokaryotes - Restriction systems - cleavage of dsDNA at specific sites
33
What is the Baltimore classification scheme for viruses?
Relationship of viral genome to mRNA
34
mRNA is always ____ orientation
+
35
Describe T4: Virulent bacteriophage.
- dsDNA with 168, 903 bp, 250 proteins - Circurlarly permuted - 5 hydroxymethylcytosine instead of cytosine - Glucosylated, resistant to restriction enzymes
36
Describe the Lytic pathway.
1. Viral DNA replicates 2. Coat proteins synthesized; virus particles assembled 3. Lysis
37
Describe the Lysogenic pathway.
1. Viral DNA is integrated into host DNA. | 2. Cell division.
38
How is lambda integrated into the host chromosome?
1. Cyclizes at cohesive ends 2. Site-specific nuclease creates staggered ends of phage and host DNA 3. Integration of lambda DNA and closing of gaps by DNA ligase
39
Linear dsDNA except for 5'-overhands...
that are complementary to one another (cos)
40
Lambda integrase recognizes attachment...
on both viral and host genomes.
41
cI
Represses all other lambda-encoded proteins | -lysogenic
42
Cro
represses cII and CIII, which induce CI | -lytic
43
For lysogeny:
- production of late proteins prevented | - lambda must be in host genome
44
RNA genome replicated for retroviruses via...
a DNA intermediate
45
What enzyme is involved in making retroviruses?
Reverse transcriptase
46
What is made by reverse transcriptase?
2 identical RNA + molecules
47
Specific tRNA to act as...
primer in retroviruses
48
gag
codes for structural retroviral proteins
49
pol
codes for reverse transcriptase and integrase
50
env-
codes for envelope proteins
51
Negative strand RNA animal virus:
Orthomyxoviruses
52
Orthomyxoviruses characteristics:
- Influenza virus - Genome segmented into 8 pieces - Helical nucleocapsid - Pleomorphic shape - Hemagglutinin - Neuraminidase
53
Hemagglutinin
the clumping of red blood cells | -antibodies to this prevent infection
54
Neuraminidase
breaks down sialic acid of cytoplasmic membrane to promote virus assembly and release
55
Antigenic drift
mutation in genes encoding NA and HA | -Yearly influenza vaccine needed
56
Antigenic shift
one cel infected with 2 different influenza viruses, reassortment of genes for surface proteins, no immunity -Pandemics and epidemics
57
Influenza virus reassortments
Pandemics-10-40 years apart | Spanish flu-1918-50 to 100 million people infected, 2 million died in U.S.
58
Subviral entities: defective viruses
- Helper viruses and defective viruses - Satellite viruses - Adeno-associated virus depends on adenovirus - Sputnik depends on mamvirus
59
Viroids
- Infectious circular RNA (lacks protein and capsid) | - 246 to 399 nucleotides stabilized by secondary structure
60
Viroid disease
- Opportunistic pathogen | - Mechanism unknown
61
Prions
- Infectious protein (lacks nucleic acid) | - Transmissable spongiform encaphalopathies
62
Transmissable spongiform encaphalopathies
- Scrapie in sheep - Bovine spongiform encephalopathy - Creutfeld-Jakob disease - Consumption of infected nervous tissue
63
Mechanisms of prion disease
- Infectious prion disease - Sporadic prion disease - Inherited prion disease
64
Zombie apocalypse
Baculovirus and caterpillars • Changes how host responds to light • Uninfected – climb up and down, rest at bo[om as pupae • Infected – climb to top of plant, die, shed virus below, eaten by birds
65
Study slides 6, 12, 19, 20, 21, 23, 27, 28, 30, and 38.
Study slides 6, 12, 19, 20, 21, 23, 27, 28, 30, and 38.

Micobiology (19 decks)

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