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Medicine 1.1 > Viruses > Flashcards

Viruses Flashcards

1
Q

What is the virion?

A

-Complete fully assembled virus particle

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2
Q

What are some general things in a virus?

A
  • Will have either DNA or RNA nucleic acid genome, but not both.
  • Can be linear or cicular
  • Can be single stranded or double stranded
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3
Q

What are the components of the basic virion?

A

-Capsid; protein containing structure designed to protect the genome and facilitate entry to the host
Capsid made from capsomeres.
-Nucleocapsid; is complete unit of nucleic acid + capsid
-May also contain essential or accessory enzymes to facilitate initial replication.
Distinctive symmetry will be helical or icosahedral

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4
Q

What is an enveloped virus derived from?

A

The host cell membrane

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5
Q

What are enveloped viruses made of?

A

-Composed of lipids, with virus proteins and glycoproteins inserted

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6
Q

What is the function of the matrix protein?

A

Viral assembly by binding the nucleocapisd core to the viral envelope during the budding process.

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7
Q

How do viruses live?

A
  • Viruses depend on living organisms to produce a host, not capable of growth or reproduction outside a living cell. Depend on biochemical machinery of host for replication.
  • Viruses can infect a range of hosts; humans, animals, plants and bacteria.
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8
Q

What is viral tropism?

A

Is ability of a given virus to productively infect a:
-particular cell (cellular tropism)
-tissue (tissue tropism)
-host species (host tropism)
-Most viruses infect only specific types of cells and tissues in one host.
-

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9
Q

What determines the host range of a virus?

A

Is determined by specific host attatchment sites and cellular factors.

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10
Q

How can viruses be transmitted?

A
  • Orally
  • Direct skin contact
  • Droplet transmission
  • Sexual
  • Direct implication
  • Trans-placental
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11
Q

What are some examples of diseases caused by viruses?

A
  • SARS; SARS CoV
  • COVID-19; SARS CoV-2
  • Influenza virus
  • MMR
  • HIV/AIDS
  • Zika
  • Ebola
  • Viral pneumonia; resp. synctial virus
  • Common cold; rhinoviruses
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12
Q

How do viruses generally enter the cell and give some examples?

A

Generally by a form of endocytosis

eg. macrophagocytosis; once virus attatches to host cell it can be engulfed by host hell membrane
eg. membrane fusion; where virus inserts itself into the host cell

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13
Q

What are the 6 steps of viral infection and replication?

A
  1. Attatchment
  2. Penetration
  3. Uncoating
  4. Replication
  5. Assembly
  6. Virion Release
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14
Q

What happens during the attatchment phase of viral infection?

A

Viral proteins on capsid or phospholipid envelope interact with specific receptors on the host cellular surface.

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15
Q

What happens during the penetration phase of viral infection?

A

Process of attatchment can induce conformational change in viral capsid proteins or lipid envelope, that results in the fusion of viral and cellular membranes. Some DNA viruses can also enter through receptor mediated endocytosis.

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16
Q

What happens during the uncoating phase of viral infection?

A

Viral capsid is removed and degraded by viral enzymes or host enzymes, releasing the viral genomic nucleic acid.

17
Q

What happens during the replication phase of viral infection?

A

Transcription or translation of viral genome initiated. Differes between RNA and DNA viruses and viruses with opposite polarities.
This stage culminates in de novo synthesis of viral proteins and genome.

18
Q

What happens during the assembly phase of viral infection?

A

After de novo synthesis, PTM’s can occur, viral proteins are then packaged with newly replicated viral genome into new virions that are ready for release from host cell.

19
Q

What are the 2 methods by which virion release can occur?

A
  • Lysis

- Budding

20
Q

Describe the lysis method of virion release?

A
  • Results in the death of an infected host cell (cytolytic),

eg. variola major (smallpox)

21
Q

Describe the budding method of virion release?

A

-Results in the acquisition of viral phospholipid envelope. Don’t usually kill infected cell (cytopathic)

22
Q

What happens after virion release?

A

After virion release, some viral proteins remain with host cell’s membrane, acting a spotential target for antibodies.
They could also be processed and presented at the cell surface on MHC-Class 1 molecules, where T cells recognize them.

23
Q

How are RNA virsuses replicated?

A
  • In dsRNA viruses, one strand is 1st transcribed by viral polymerase into mRNA.
  • In ssRNA viruses, there are 3 distinct routes to RNA formation.
24
Q

What are the 3 routes to RNA formation for ssRNA virsues?

A
  1. SS has + sense configuration; can be used directly as mRNA.
  2. SS has - sense configuration; must be transcribed using viral polymerase into a + sense strand, which can then act as mRNA.
  3. Retroviruses follow different route.
25
Q

What route do retroviruses take for RNA formation?

A

Their + sense ssRNA is first made into - sense ssDNA, using the viral reverse transcriptase enzyme in the nucleus and becomes integrated into the host genome. The integrated viral DNA is then transcribed by host polymerase into mRNA.

26
Q

What are the possible outcomes of viral infection?

A
  1. Virus release and host cell can be destroyed by cell lysis eg.poliovirus
  2. Virus can exit by budding eg.influennza virus
  3. Virus may be mutated in the host cell cytoplasm eg. herpesvirus
  4. It can become incorporated into the genome eg.retroviruses, HepB
  5. They can become oncogenic viruses, that cause cancer.
27
Q

How is genetic variation of viruses caused?

A
  • Viruses mutate rapidly
  • Some mutations are more common in RNA viruses
  • Viruses can use gene recombination to cause extensive and sudden variations
28
Q

What is antigenic drift?

A

Small antigenic changes eg. influenza virus, HIV

29
Q

What is antigenic shift?

A

Exchange of genetic material between 2 pathogens eg. influenza A virus

30
Q

Why may viruses mutate?

A

To escape immune surveillance.

Medicine 1.1 (28 decks)

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