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MIMM 211 > Lecture 30: Virology V > Flashcards

Lecture 30: Virology V Flashcards

1
Q

Name the 6 steps of the infectious cycle.

A
  1. Attachment/absorption
  2. Penetration
  3. Uncoating
  4. Biosynthesis
  5. Assembly/maturation
  6. Release
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2
Q

What are the two broad phases of the viral infection cycle?

A

The early phase and the late phase.

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3
Q

What steps are considered part of the early phase of the viral infection cycle?

A

Attachment, penetration, uncoating, delivery of the genome to the nucleus (if needed), replication of the genome. It also includes expression of early proteins, which are needed to take control of host cells and for viral genome replication.

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4
Q

What steps are considered part of the late phase of the viral infection cycle?

A

It includes the virus assembly and release and well as the production of late proteins, which are structural, such as those forming the capsid.

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5
Q

What do viruses require for the attachment step to be successful and why?

A

Viruses require specific receptors on the surface of the host cell for its surface proteins to bind to. This is because viruses cannot diffuse passively through cell membranes.

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6
Q

What type of viral proteins can allow for attachment to a host cell?

A

Either the capsid proteins in the case of naked viruses or the glycoprotein spikes in the case of envelope viruses.

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7
Q

How can host cells resist attachment of a virus?

A

If they don’t have receptors for the viral proteins to bind to, they are resistant to infection.

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8
Q

What are the 2 possible modes of penetration for enveloped viruses?

A

They can either enter by fusion of the viral envelope with the host cell membrane or by endocytosis.

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9
Q

What are the 2 possible modes of penetration for naked viruses?

A

They can inject their genome into host cells (direct penetration) or enter by endocytosis.

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10
Q

For what types of penetration is uncoating necessary?

A

For entry via membrane fusion or endocytosis.

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11
Q

What is uncoating?

A

It is the disassembly of the viral capsid.

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12
Q

Explain how uncoating works when the virus enters via endocytosis.

A

Once the virus enters and reaches the endosome, the content of the endosome is acidified via a proton pump in the membrane. The low pH causes a disassembly of the capid components, allowing for extrusion of the viral genome into the cytosol.

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13
Q

What is the pH of the early and late endosome during uncoating?

A

< 6.2, < 5.3

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14
Q

What steps are included in the notion of viral entry?

A

Viral entry includes the earliest stages of infection, including attachment, penetration, and uncoating.

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15
Q

Describe the biosynthesis step for DNA viruses (incl. different groups).

A

Once the genome is in the nucleus, the viral proteins will be expressed and the viral genome will be replicated. For group 1 viruses, this means that the DNA will be replicated by cellular DNA polymerases, and late proteins will be made to encapsidate the genome. For group 2, it is similar (see Baltimore classification)

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16
Q

Describe the biosynthesis step for RNA viruses.

A

Once the genome is in the cytoplasm, the RNA genome is replicated and late proteins are made for encapsidation. See Baltimore classification for group specificities.

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17
Q

Describe the biosynthesis step for retroviruses.

A

Depending on the group, its RNA or DNA genome gets most replicated and is used to generate capsid proteins.

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18
Q

Name 2 different modes of assembly and release for viruses. Which types of viruses use each?

A

By cell lysis and by budding. Cell lysis is used by nonenveloped viruses, while budding is used by enveloped viruses.

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19
Q

What is assembly and release by cell lysis?

A

Nonenveloped viruses assemble in the cytoplasm or nucleus and are released by cellular lysis.

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20
Q

What is assembly and release by budding?

A

For enveloped viruses, the viral glycoproteins are inserted into the cell membrane of the host. The virus nucleocapsids bind to the part of the host cell membrane where these proteins are and bud into the extracellular space, attaching the glycoproteins in the process.

21
Q

Explain how the study of small DNA viruses led to a discovery about the host.

A

It led to the discovery of promoters for eukaryotic RNA polymerases.

22
Q

Explain how the study of cancer-producing viruses led to a discovery about the host.

A

It led to the discovery of many cellular oncogenes.

23
Q

Explain how the study of mRNA and DNA viruses led to a discovery about the host.

A

It led to the discovery of RNA splicing.

24
Q

Explain how the study of viral DNA replication led to a discovery about the host.

A

It led to a better understanding of cellular DNA replication.

25
Q

What are the 3 requirements for a successful infection.

A
  1. Enough virus
  2. Cells accessible, susceptible, and permissive
  3. Local antiviral defense absent or overcome
26
Q

Explain what the difference is between a cell that is susceptible and a cell that is permissive.

A

A cell that is susceptible needs to express the right kind of cell surface receptor that allows the virus into the cell. A cell that is permissive must express all the other host factors that the virus requires for its replication, such as specific cellular proteins. A host cell can thus be susceptible but not permissive.

27
Q

Name the 5 major patterns of virus infection.

A
  1. Abortive
  2. Acute
  3. Chronic
  4. Persistent
  5. Latent
28
Q

What is an abortive infection?

A

It is when the cells are susceptible but not permissive, leading to an unsuccessful infection.

29
Q

What is an acute infection?

A

When there’s the maximum amount of virus in the blood/lung/other location.

30
Q

What is a chronic infection?

A

It is an infection that persists over time and makes you sick.

31
Q

What is a persistent infection?

A

Similar to a chronic infection, it is an infection that persists over time and makes you sick.

32
Q

What is a latent infection?

A

It is like a chronic infection in that it lasts a long time, but it does not actively make you sick.

33
Q

What is viral tropism?

A

The specificity of a virus for a particular cell type, tissue, and/or host.

34
Q

What are the 3 possible types of viral tropism?

A

Cellular, tissue, or host

35
Q

Describe the cellular tropism of HIV.

A

It normally infects macrophages.

36
Q

Describe the tissue tropism of influenza.

A

It normally infects lung tissue.

37
Q

Describe the host tropism of myxoma.

A

It normally infects rabbits, not humans.

38
Q

After replication at the site of entry, where do viruses go?

A

They can either remain localized in a given tissue or system or can spread beyond the primary site of infection and become disseminated.

39
Q

What is required for an infection to be considered systemic?

A

If it spreads beyond the primary site of infection and enough organs become infected, it becomes a systemic infection. But it still must breach the physical and immune barriers if it wants to spread.

40
Q

What is pathogenesis?

A

The process of producing a disease.

41
Q

Name 3 possible modes of virus transmission.

A

Person to person, animal to animal with humans as accidental hosts, or transmission by an arthropod vector.

42
Q

Give 5 examples of how person to person virus transmission can occur.

A
  1. Droplet or aerosol infection
  2. Fecal-oral route
  3. Sexual contact
  4. Transfusion of contaminated blood
  5. Hand-mouth, hand-eye, or mouth-mouth contact
43
Q

Give 2 examples of how animal to animal virus transmission with humans as accidental hosts can occur.

A
  1. By bite
  2. By droplet or aerosol infection from contaminated areas.
44
Q

Give an example of how transmission by an arthropod vector can occur.

A

Via moquito bite.

45
Q

What is the difference between horizontal and vertical transmission?

A

Horizontal transmission involves transmission between members of the same species, while vertical transmission involves transmission between parent and offspring.

46
Q

What is germ line transmission?

A

It is when the agent is transmitted as part of the genome.

47
Q

What is nosocomial transmission?

A

When an individual is infected while in hospital or health care facility.

48
Q

What is zoonosis?

A

Any disease or infection that is naturally transmissible from vertebrate animals to humans. It can be bacterial, viral, or parasitic.

MIMM 211 (38 decks)

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