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AD1 > JM - viral pathogenesis > Flashcards

JM - viral pathogenesis Flashcards

1
Q

If a virus has a low number of genes, how does this affect the host cell?

A

There is a higher percentage of the genome that codes for proteins. The host cell is more likely to supply more of the raw materials.

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2
Q

What does the viral genome not code for?

A
  • Ribosomes, tRNA or protein synthesis enzymes.
  • Genes for lipid or AA synthesis or energy metabolism.
  • (Less) non-coding DNA, introns and control sequences.
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3
Q

What can +ve ssRNA bind to?

A

Genome can bind to the ribosome and translate to a protein.

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4
Q

What can -ve ssRNA bind to?

A

The genome cannot bind directly to the ribosome

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5
Q

What is a capsid?

A

Protein that encloses the viral nucleic acid

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6
Q

What is a capsomer?

A

Multiple protein subunits within the virus

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7
Q

What is a nucelocapsid?

A

Both the nucleic acid and the capsid

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8
Q

What is the function of proteins within the virus?

A
  • Packaging of the genome and enzymes.
  • Protection of the nucleic acid from UV light.
  • Protection from nucleases.
  • Provides specificity for the attachment of the virus.
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9
Q

Describe the 3 structures that proteins can take within a virus.

A
  1. Can form a hexagonal array, which is flat sheet. This can be rolled to form a cylinder, which has helical symmetry. new molecules can be added like steps in a staircase.
  2. Pentagon can be surrounded by hexagons to form a spherical shape. This requires 12 pentagons, and the size of the sphere can increase, if the number of hexagons are increased.
  3. Icosahedron. Triangles are arranged as overlapping pentamers. 5, 3 and 2 fold symmetry allows for space to be saved within the genome.
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10
Q

Where is the virus’ envelope derived from?

A

The host cell

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11
Q

Which viruses have an envelope?

A

Helical viruses and many icosahedral viruses.

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12
Q

What is a peplomer?

A

Membrane anchored glycoprotein sugar added by host cell enzymes in the golgi apparatus.

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13
Q

What are the 5 ways that a virus can enter the host?

A
  • Respiratory route
  • Oral route
  • Cutaneous localised infection
  • Percutaneous injection
  • Sexually transmitted infection
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14
Q

Why is HIV and FIV restricted to its own species?

A

HIV binds with a high affinity to CD4 receptors on human T-cells. This causes a conformational change to allow a low affinity interaction with chemokine receptor CCRS/CXCR4.
FIV binds with a high affinity to CD134 receptors on cat T-cells. This causes a conformational change to allow a low affinity interaction with chemokine receptor CXCR4.

Human CD134 cannot replace cat CD134.
Human CXCR4 can replace cst CD134.

The fact that HIV must bind to CD4 to causes a conformational change initially, means that it is restricted to its species.

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15
Q

Why can influenza cross species?

A

Influenza hemagglutinin binds to sialic acid, which is a widespread ligand, and so increases the chance for a cross species infection.

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16
Q

How does a lytic infection affect the cells?

A

Releases viral particles into the environment.
This causes an extensive loss of function because many more cells can be infected.
Many acute viral infections end in cell death.

17
Q

How does a latent infection affect the cells?

A

Persists within a cell and does not cause cell death.
New viral particles are released without killing the cell.
Can persist for the lifetime of the host.
Acts as a source of infection for others.

18
Q

How does a persistent infection affect the host?

A

Associated with the failure of the immune system to clear the virus.

19
Q

How does enhanced cell growth affect the host?

A

Viruses can manipulate cell replication to increase the number of cell divisions and expand the number of infected cells.

20
Q

During a viral infection, what causes an inflammatory response?

A

Poly U tails initiate an inflammatory response, as these are found on -ve ssRNA.
Interferons allows for neighbouring cells to prepare for the viral infection.
Increased MHC expression
Activated macrophages and dendrites.
Recruited and activated NK cells.

21
Q

What is a plaque assay used for? (In terms of viruses)

A

To show the replication competence.

Holes are where the cells have died

22
Q

How does a virus replicate within a host cell?

A
  • Attachment to plasma membrane
  • Entry into the cytoplasm/nucleus
  • Uncoating of the viral particle
  • Synthesis of mRNA and proteins
  • Replication of nucleic acid
  • Virus assembly
  • Exit of virus from the cell
23
Q

Describe the reading frame of a virus.

A

Start codon - AUG
Ribosome reads the genome until it reaches AUG, and then the polypeptide is assembled.
Until the ribosome reaches a stop codon.

24
Q

Why must all viruses produce mRNA?

A

So that the genome can bind to a ribosome and be encoded to make proteins.

25
Q

What reaction does virus RNA polymerase catalyse?

A

-ve sense RNA into +ve sense RNA. This is so that the genome can bind to the ribosome.
The virus must carry this with them when they infect a host cell.

26
Q

How do retroviruses make proteins?

A

They have a diploid +ve ssRNA, the only virus to have this.
Reverse transcriptase - this forms dsDNA.
Integrase - integrates dsDNA into the host genome.
mRNA+ - formed from using the host cell RNA polymerase.

27
Q

What does the FMD virus bind to?

A

It binds to the RGD motif on molecules that are found in the basement membrane.
This is found in high density on basal epithelial cells.

28
Q

How does FMD enter cells?

A

Receptor mediated endocytosis via clarthyrin coated pits.

29
Q

What happens during the uncoating of the FMD virus?

A

H+ ions are pumped into the endosome, which causes the pH in the vesicles to drop.
The drop in pH causes a pore to form in the endosome membrane. The virus exits the cell before it is digested.

30
Q

How is mRNA and protein synthesised with FMD virus?

A
  • In the cytoplasm, the VPG is dissociated from the 5’ end.
  • +ve sense RNA already has a polyA tail, without a cap.
  • 5’ end has an internal ribosome entry site. This allows ribosomes to bind and initiate translation.
  • This makes 1 large polyprotein.
31
Q

What is the function of the polyprotein produced by the FMD virus?

A

To acts as a proteolytic enzyme. So it can cut itself into pieces.

32
Q

How does the FMD replicate within the cell?

A
  • RNA polymerase uses VPG as a primer.

- This copies the +ve sense RNA to a -ve sense RNA.

33
Q

How is the FMD virus assembled?

A

The genome binds to a VPG protein and are packaged within self-assembling capsids.

34
Q

How does FMD destroy host cell enzymes?

A

1 virus required 60 polypeptide chains. This means that large amounts of RNA polymerase and RNA virus proteases to destroy host capping enzymes.

35
Q

How is the FMD virus released from it’s cell?

A
  • There is a loss of host cell protein synthesis. So all cell vital functions are compromised.
  • Cell swells and bursts due to a lack of ion pumps. This releases the newly synthesised viral particles.

AD1 (19 decks)

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