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BIOL 240 > Module 5 > Flashcards

Module 5 Flashcards

Viruses

1
Q

what was the first virus discovered?

A

tobacco mosaic virus

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2
Q

who discovered viruses

A

Dimitri Ivanovsky

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3
Q

who discovered bacteriophages

A

Felix d’Herelle

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4
Q

who discovered yellow fever virus

A

Walter Reed in the US Army

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5
Q

why was the discovery of the yellow fever virus unethical

A

Reed researched on military participants
put mosquitoes on healthy individuals to test if they caused it

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6
Q

compare the size of viruses to bacteria

A

~1/100th the length of a bacterial cell
the genome is much smaller

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7
Q

how does the DNA of viruses differ

A

some are encoded by RNA, others DNA
can be single-stranded or double-stranded
closed and circular or linear

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8
Q

definition: capsid

A

protein shell that encircles the virus’ genome

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9
Q

definition: nucleocapsid

A

capsid + genome

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10
Q

definition: envelope

A

additional layer of the outside of the nucleocapsid (not always present)

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11
Q

where does the material for viral envelopes come from

A

any membrane, e.g. plasma membrane, nuclear membrane, ER

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12
Q

what are the capsid structures

A

helical (exact length required to enclose the genome)
icosahedral (20 triangles, each triangle is 3 linear polypeptides)
complex (e.g. syringe-like shape)

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13
Q

what is the shape of the smallpox virus

A

shaped like dumbbells
enclosed within a circular membrane

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14
Q

what are examples of enveloped viruses

A

viruses for:
smallpox
influenza
HIV
Ebola

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15
Q

what are examples of non-enveloped viruses

A

poliovirus
tobacco mosaic virus

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16
Q

what are the steps for virus replication

A

attach to host cell
enter the cell
uncoat
replicate genome
expression
assembly
exit

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17
Q

what is needed for a virus to attach to the host cell

A

must recognize specific:
cell-surface proteins
proteins modified w/ specific sugars
polysaccharides

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18
Q

what are ways viruses get into animal cells

A

enveloped virus: endocytosis or membrane fusion
non-enveloped virus: endocytosis

19
Q

describe endocytosis of viruses

A
  1. virus attaches to specific cell receptor
  2. endocytosis is initiated
  3. virus is enclosed in an endosome

if virus is non-enveloped:
virus is released and uncoats to release the genome

if virus is enveloped:
low pH of the endosome initiates fusion of the viral envelope w/ the endosome membrane

20
Q

why is it harder to infect plant cells

A

viruses can’t get through cell wall
can only access the cell if the wall is damaged or broken externally

21
Q

how do viruses infect bacterial cells

A
  1. tail fibers attach to receptors
  2. conformational change in the tail fibers bring base of the tail in contact with the host cell surface
  3. rearrangement of tail proteins allows inner core tube proteins to extend down into cell wall
  4. contact with plasma membrane initiates transfer of DNA through a pore formed in the lipid bilayer
22
Q

definition: lytic/virulent phages

A

only undergo the lytic cycle

23
Q

definition: temperate phages

A

undergo both lytic and lysogenic cycles

24
Q

why is the lysogenic cycle advantageous

A

it allows the virus to be stable for many generation
doesn’t immediately lyse the cell

25
Q

definition: prophage

A

stably maintained viral genome within a cell

26
Q

what causes the cell to return back to the lytic cycles

A
  • some form of stress, e.g. exposure to UV light, DNA damage
  • influx of nutrients, cells begin dividing
27
Q

what are the theories for the origin of viruses

A

coevolution hypothesis: viruses have been around for a long time, may have been encoded before cellular life
regressive hypothesis: were originally cellular organisms, lost genes they no longer needed
progressive hypothesis: the right combinations of genetic material were put together (plausible b/c plasmids exist)

28
Q

how do you cultivate bacteriophages

A
  1. small of volume of susceptible bacterial host cells are added to the phage sample
  2. mixture is added to the molten nutrient agar and quickly mixed
  3. agar mixture is poured onto a nutrient agar base and allowed to solidify
  4. plaques appear after sufficient incubation
29
Q

what are ways to cultivate animal viruses

A
  • prepare the virus in fertilized eggs of chicken or ducks
  • grown in tissue culture
  • many animal virus cultivation methods are dependent on the first human cell line, HeLa cells
30
Q

what are ways to purify viruses

A

filtration
differential centrifugation
gradient centrifugation

31
Q

what are ways to quantify viruses

A

direct count
hemagglutination assay
plaque assay
endpoint assay: TCID50 and LD50

32
Q

where are virus particles in a gradient centrifugation

A

beneath cell debris

33
Q

how is a gradient centrifugation made

A

successively filling layers of decreasing concentration of sucrose

34
Q

which ways of quantifying viruses differentiates between infectious and noninfectious ones

A

plaque assay
endpoint assay

35
Q

how are viruses historically named

A

simple letter/number combinations
organisms they infect
place they were discovered
appearance
disease caused

36
Q

what are standardized ways of naming

A

International Committee on Taxonomy of Viruses (ICTV)
Baltimore Classification System

37
Q

what are some characteristics involved with ICTV naming

A

virion morphology
genome structure
biological features

38
Q

what is the Baltimore Classification System based on

A

based on the viruses genome
there are 7 classes that encompass all possible genome characteristics

39
Q

what are ways to identify viruses

A

observe under an electron microscope
nucleic acid analysis

40
Q

what are some virus-like particles

A

viroids - RNA with some spectacular secondary structure
prions - proteinaceous infectious particles

41
Q

how is virology used in medicine

A

cancer-causing oncoviruses
cancer-destroying oncolytic viruses
gene therapy

42
Q

where are viroids found

A

only in plants

43
Q

what causes mad cow disease & Creutzfeldt-Jacob disease

A

prions

44
Q

what is CRISPR

A

a mechanism that bacteria use to prevent infection by viruses

BIOL 240 (12 decks)

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