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MCIM 224 > 9 Viruses (1) > Flashcards

9 Viruses (1) Flashcards

1
Q

Define “virus”

A

A subcellular agent that must use the metabolic machinery of a living host to produce NEW virus particles

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2
Q

Are viruses cellular or non-cellular?

A

non-cellular

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3
Q

Two basic components of a virus particle?

A
  1. Nucleic acid (genetic info)

2. Protein coat

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4
Q

What does it mean for a virus to be an “obligate intracellular parasite”?

A

Viruses must enter a cell before they can infect and reproduce

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5
Q

Viruses are much ______ than bacterial cells

A

smaller

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6
Q

Avg size of a virus?

A

20-300 nm

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7
Q

T or F: Viruses are easily seen using a light microscope.

A

F

Viruses can only be seen w/ electron microscopes

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8
Q

Would a filter of 0.2 microns be useful in filtering out viruses?

A

No. Viruses are usually smaller than 0.2 microns (200 nm).

[Viruses are usually 20-300 nm]

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9
Q

T or F: Viruses are very diverse in appearance, size, and shape.

A

T

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10
Q

Name the three structural features of a virus:

A
  1. Nucleic acid core
  2. Protein coat (aka “capsid”)
  3. +/- Envelope (surrounds the capsid)
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11
Q

Two types of viruses in terms of nucleic acid core.

A
  1. DNA viruses
  2. RNA viruses
    [Note: A virus will NEVER have both DNA and RNA]

Can be either single OR double stranded.

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12
Q

The protein coat (capsid) of a virus is composed of _____ subunits

A

capsomere

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13
Q

Two types of viruses in terms of envelope.

A
  1. Naked virus

2. Enveloped virus

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14
Q

If a virus is enveloped, what is the envelope made up of?

A

Lipids

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15
Q

A(n) ____ virus is composed of a nucleic acid core and a capsid coat.

A

naked

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16
Q

A(n) ____ virus is composed of a nucleic acid core, a capsid coat, and a lipid envelope around the capsid.

A

enveloped

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17
Q

Glycoprotein spikes are attached to the _____ in naked viruses.

A

capsid

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18
Q

Glycoprotein spikes are attached to the _____ in enveloped viruses.

A

envelope

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19
Q

T or F: A virus can infect any type of living cell.

A

F

Viruses have a defined HOST RANGE (i.e. they can only infect one type of cell or host)

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20
Q

What is host range (i.e. range of hosts a virus can infect) determined by? (2)

A
  1. Presence of receptors on host cell

2. Presence of suitable metabolic machinery in host cell

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21
Q

T or F: Viruses are restricted to the types of cells they can infect.

A

T

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22
Q

T or F: Viruses are inert when outside of host cell.

A

T

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23
Q

5 basic steps of a virus’ life cycle?

A
  1. Adsorption
  2. Penetration/uncoating
  3. Gene expression
  4. Assembly
  5. Release
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24
Q

What facilitates a virus’ ability to adsorb onto a host cell?

A

Virus “spike” glycoproteins

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25
Q

The interaction b/w what two structures is an important determinant of the virus’ host range and tissue specificity?

A

The glycoprotein spike’s interaction w/ the host cell’s receptor

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26
Q

What is the pharmacological significance of the adsorption step of the life cycle of viruses?

A

This step could potentially be blocked by drugs/vaccinations

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27
Q

T or F: Human viruses use the SAME receptor type in the human body

A

F

Diff viruses use diff receptors

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28
Q

5 basic steps of a virus’ life cycle?

A
  1. Adsorption
  2. Penetration/uncoating
  3. Gene expression
  4. Assembly
  5. Release
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29
Q

After adsorbing, what process do naked viruses use to penetrate into cells?

A

receptor-mediated ENDOCYTOSIS

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30
Q

After adsorbing, what process do enveloped viruses use to penetrate into cells?

A

receptor-mediated FUSION

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31
Q

This virus type is surrounded by a vesicle once it gains entry into the host’s cell.

a. Naked virus
b. Enveloped virus

A

Naked virus

32
Q

Membrane fusion occurs w/ this virus type as it gains entry into the host cell.

a. Naked virus
b. Enveloped virus

A

Enveloped virus

33
Q

Which step in a virus’ life cycle corresponds to the event of viral nucleic acids being transcribed, translated, and replicated via the host cell’s enzymes?

A

Gene expression

34
Q

What occurs during “assembly” - the fourth step in a virus’ life cycle?

A

New virus particles are produced and assembled (e.g. capsids, nucleic acids, etc.)

35
Q

What occurs during the “release” phase of a virus’ life cycle?

A

Mature, infectious viruses are released from the host cell

36
Q

T or F: The release of naked viruses does not kill the host cell.

A

F

The host cell is lysed due to the accumulation of naked viruses inside of it.

37
Q

T or F: The release of enveloped viruses does not necessarily kill the host cell right away.

A

T

38
Q

Where does the envelope of enveloped viruses come from?

A

The host cell’s membrane (as the capsid buds out)

39
Q

5 basic steps of a virus’ life cycle?

A
  1. Adsorption
  2. Penetration/uncoating
  3. Gene expression
  4. Assembly
  5. Release
40
Q

Naked viruses are released via…

A

host cell LYSIS

41
Q

Enveloped viruses are released via…

A

BUDDING

42
Q

Why don’t antibiotics work on viruses?

A

Viruses do not contain - at any point in its life cycle -

the same biological targets as bacteria

43
Q

List the 4 types of viral infections:

A
  1. Lytic (acute) infection
  2. Persistent (chronic) infection
  3. Latent infection
  4. Oncogenic infection (“Host Cell Transformation”)
44
Q

This type of viral infection is associated w/ viral nucleic acids being inserted into the host cell’s chromosome.

A

Latent infection

45
Q

Viruses can be REACTIVATED in this viral infection type.

A

Latent infection

46
Q

This viral infection is associated w/ low-level, continuous release of viruses over a longer period of time

A

Persistent (chronic) infection

47
Q

This viral infection is associated w/ rapid virus replication and host cell death upon release.

A

Lytic (acute) infection

48
Q

Disease symptoms are usually less severe in this viral infection type, despite virus particles constantly being present in the infected person.

A

Persistent (chronic) infection

49
Q

Why is it so easy for viruses to be spread?

A

Bc the presence of infectious virions are not necessarily associated w/ the presence of disease symptoms.

That is, just because a person is infected doesn’t mean that he/she is experiencing negative effects, and so they may think that they’re healthy and non-infectious, but the contrary is true.

50
Q

This viral infection type is associated w/ viruses that can cause their host cell to grow in an unctrled way.

A

Oncogenic infection

51
Q

What’re two virus-related mechanisms of oncogenesis?

A
  1. Viral nucleic acids inserted into host’s chromosome disrupts the host cell’s ability to ctrl its growth
  2. Viral proteins produced during virus’ life cycle destroy/inhibit host cell factors that’re needed to ctrl host cell growth
52
Q

What is a potential problem with using anti-viral agents?

A

The virus’ life cycle is closely linked to the host cell’s processes > difficult to target the virus without damaging the host cell

53
Q

T or F: There’re relatively few anti-viral agents compared to anti-bacterial agents.

A

T

54
Q

T or F: Due to commonalities in viral life cycles amongst all viruses, there’re more broad-spectrum anti-virals than there are broad-spectrum anti-bacterials.

A

F

There’re only a few agents that’re truly “broad-spectrum” anti-viral

55
Q

How do current anti-virals work?

A

By interrupting some part of the viral life cycle.

56
Q

Do current anti-virals kill pre-existing viruses?

A

No, they only block the production of new viruses in the host cell

57
Q

What are the most ideal steps in the virus life cycle to block via anti-viral agents? (2)

A
  1. Adsorption

2. Penetration

58
Q

Selzentry is an anti-viral agent for HIV treatment. How does it work?

A

It binds on the receptor that HIV usually binds to > prevents HIV from binding

59
Q

Docosanol (Abreva TM) is used in the treatment of herpes. How does it work?

A

It’s a fatty alcohol that becomes incorporated into the host cell’s membrane > prevents herpes virus from fusing w/ the host cell’s membrane

60
Q

What is the purpose of anti-virals that block the uncoating step (step 2 of viral life cycle) of viruses?

A

The purpose is to prevent the breakdown of the capsid by binding to it, and thus viral nucleic acids cannot be released into the host cell

61
Q

Why are anti-virals that block the uncoating of viral nucleic acids highly virus-specific?

A

Because diff viruses have diff capsid structures

62
Q

What type of anti-viral drugs are present in the greatest variety w/ reasonable selective action?

A

Drugs that block viral gene expression and replication (step 3 of the viral life cycle)

63
Q

Name two types of drugs that block viral gene expression and replication:

A
  1. Viral polymerase inhibitors

2. Nucleic acid analogues

64
Q

What is foscarnet, and what does it do?

A

It is a viral polymerase inhibitor, and it binds to the viral DNA polymerase of cytomegalovirus and HSV > no new viral DNA is produced

65
Q

What is acyclovir?

A

It’s a guanine analogue that’s used in HSV treatment

66
Q

What is azidothymidine?

A

It’s a thymine analogue that’s used in HIV treatment

67
Q

Why is acyclovir given in a pro-drug form?

A

So that it doesn’t have activity in non-infected cells > reduces toxicity

68
Q

Name two types of anti-viral drugs that block viral assembly (step 4) or viral release (step 5 of viral life cycle).

A
  1. Protease inhibitors

2. Neuraminidase inhibitors

69
Q

What’re the proteases that’re produced by some viruses needed for?

A

For the synthesis and ASSEMBLY of viral structural proteins

70
Q

What is neuraminidase?

A

It’s an enzyme produced by the influenza virus that’s needed for its RELEASE

71
Q

Oseltamivir and zanamivir are examples of what type of antiviral?

A

Neuraminidase inhibitors (blocks the release of influenza viruses from host cells)

72
Q

What’s interferon? What does interferon do?

A

A NATURALLY-PRODUCED anti-viral chemical. It’s released by virus-infected cells and signals to neighbouring cells to make various anti-viral factors.

73
Q

MOST anti-virals act at this step of the viral life cycle.

A

Genome replication

74
Q

5 types of anti-viral agents?

A
  1. Drugs that block viral adsorption and penetration (steps 1 and 2)
  2. Drugs that block un-coating of viral nucleic acids (step 2)
  3. Drugs that block viral gene expression and replication (step 3)
  4. Drugs that block viral assembly and/or release (steps 4 and 5)
  5. Interferon
75
Q

Name 5 problems w/ anti-viral agents.

A
  1. Many are toxic in varying degrees
  2. Latent viruses (i.e. those that aren’t actively replicating constantly) are not susceptible
  3. Some anti-virals are less effective if given late in the infection
  4. Resistance can develop quickly
  5. New agents are difficult to develop
76
Q

Why are latent viruses a problem when it comes to anti-viral therapies?

A

Most anti-viral therapies specifically target viral replication, so most drugs currently available are useless against latent viruses

77
Q

Why is developing new anti-virals a challenge?

A

Few animal models for human viruses

[Remember: Viruses have a defined host range, so human viruses affect ONLY humans, thus can’t test anti-virals in other organisms]

MCIM 224 (25 decks)

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