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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
Q

What happens during the eclipse stage of the viral growth curve?

A

Infectious particles cannot be detected

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26
Q

Describe the attachment of a virus to a host cell.

A
  • External virus protein interacts within host cell “receptor”
  • Receptors must be present for infection to occur
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27
Q

What are 3 receptor proteins involved in virus attachment?

A

– ɸTI—iron uptake protein
– ɸʎ—maltose uptake protein
– HIV—CD4 on helper T cells (recogni7on of MHC
an7gens)

28
Q

• Receptors must be present for infec7on to occur

A

Absence

– Mutation

29
Q

What is penetration?

A

Entry of viral genome into host cell

30
Q

What is uncoating?

A

Virus looses outer coat

31
Q

What protein is involved in penetration?

32
Q

What are some host defenses to viruses?

A
  • Limit attachment
  • RNA mechanisms
    • RNAi-eukaryotes
    • CRISPR-prokaryotes
  • Restriction systems
    • cleavage of dsDNA at specific sites
33
Q

What is the Baltimore classification scheme for viruses?

A

Relationship of viral genome to mRNA

34
Q

mRNA is always ____ orientation

35
Q

Describe T4: Virulent bacteriophage.

A
  • dsDNA with 168, 903 bp, 250 proteins
  • Circurlarly permuted
  • 5 hydroxymethylcytosine instead of cytosine
  • Glucosylated, resistant to restriction enzymes
36
Q

Describe the Lytic pathway.

A
  1. Viral DNA replicates
  2. Coat proteins synthesized; virus particles assembled
  3. Lysis
37
Q

Describe the Lysogenic pathway.

A
  1. Viral DNA is integrated into host DNA.

2. Cell division.

38
Q

How is lambda integrated into the host chromosome?

A
  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
Q

Linear dsDNA except for 5’-overhands…

A

that are complementary to one another (cos)

40
Q

Lambda integrase recognizes attachment…

A

on both viral and host genomes.

41
Q

cI

A

Represses all other lambda-encoded proteins

-lysogenic

42
Q

Cro

A

represses cII and CIII, which induce CI

-lytic

43
Q

For lysogeny:

A
  • production of late proteins prevented

- lambda must be in host genome

44
Q

RNA genome replicated for retroviruses via…

A

a DNA intermediate

45
Q

What enzyme is involved in making retroviruses?

A

Reverse transcriptase

46
Q

What is made by reverse transcriptase?

A

2 identical RNA + molecules

47
Q

Specific tRNA to act as…

A

primer in retroviruses

48
Q

gag

A

codes for structural retroviral proteins

49
Q

pol

A

codes for reverse transcriptase and integrase

50
Q

env-

A

codes for envelope proteins

51
Q

Negative strand RNA animal virus:

A

Orthomyxoviruses

52
Q

Orthomyxoviruses characteristics:

A
  • Influenza virus
  • Genome segmented into 8 pieces
  • Helical nucleocapsid
  • Pleomorphic shape
  • Hemagglutinin
  • Neuraminidase
53
Q

Hemagglutinin

A

the clumping of red blood cells

-antibodies to this prevent infection

54
Q

Neuraminidase

A

breaks down sialic acid of cytoplasmic membrane to promote virus assembly and release

55
Q

Antigenic drift

A

mutation in genes encoding NA and HA

-Yearly influenza vaccine needed

56
Q

Antigenic shift

A

one cel infected with 2 different influenza viruses, reassortment of genes for surface proteins, no immunity
-Pandemics and epidemics

57
Q

Influenza virus reassortments

A

Pandemics-10-40 years apart

Spanish flu-1918-50 to 100 million people infected, 2 million died in U.S.

58
Q

Subviral entities: defective viruses

A
  • Helper viruses and defective viruses
  • Satellite viruses
  • Adeno-associated virus depends on adenovirus
  • Sputnik depends on mamvirus
59
Q

Viroids

A
  • Infectious circular RNA (lacks protein and capsid)

- 246 to 399 nucleotides stabilized by secondary structure

60
Q

Viroid disease

A
  • Opportunistic pathogen

- Mechanism unknown

61
Q

Prions

A
  • Infectious protein (lacks nucleic acid)

- Transmissable spongiform encaphalopathies

62
Q

Transmissable spongiform encaphalopathies

A
  • Scrapie in sheep
  • Bovine spongiform encephalopathy
  • Creutfeld-Jakob disease
  • Consumption of infected nervous tissue
63
Q

Mechanisms of prion disease

A
  • Infectious prion disease
  • Sporadic prion disease
  • Inherited prion disease
64
Q

Zombie apocalypse

A

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
Q

Study slides 6, 12, 19, 20, 21, 23, 27, 28, 30, and 38.

A

Study slides 6, 12, 19, 20, 21, 23, 27, 28, 30, and 38.

Micobiology (19 decks)

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