12 - Classification of viruses

Question 1

How can viruses be classified?

Answer 1

By their geometry
by their host organism,
by wether they have envelopes,
by the place the viruses were discovered
by their cytopathology during infection

Question 2

How does the Baltimore Classification System classify viruses?

Answer 2

The basis of their unique pathway from genome to mRNA

Question 3

What is the difference between +ssRNA and -ssRNA

Answer 3

+ssRNA is ready to be translated, where as -ssRNA is complimentary to +ssRNA and needs to be converted to +ssRNA to be be used in translation

Question 4

What are the four ways in which a virus can infect a cell?

Answer 4

• transform cells to tumour cells
• cell lysis (and viral release)
• persistent infection (slow release of virus without cell death)
• latest infection (virus present and causing no harm until it becomes a lytic infection later)

Question 5

What are the six steps in the viral life cycle?

Answer 5

1. Attachment
2. Uncoating
3. Replication
4. Biosynthesis
5. Assembly
6. Budding

Question 6

What are the three possible entry mechanisms that allow viruses to enter cells?

Answer 6

• injection of nucleic acid
• fusion of envelope with host membrane
• endocytosis

Question 7

What two things need to be generated in the replication stage?

Answer 7

Viral proteins (mRNA synthesis)
Viral genome (generation of viral genetic material)

Question 8

Describe the structure of the rhabdoviruses

Answer 8

• bullet shaped virion
• enveloped
• -ssRNA

Question 9

How is rabies transmitted?

Answer 9

through saliva

Question 10

What part of the body does the rabies virus effect?

Answer 10

The peripheral and central nervous system (including the brain)

Question 11

What are the two types of rabies?

Answer 11

furious and dumb

Question 12

Furious rabies

Answer 12

• 80-90% of cases (Mortality rate -100%)
• Change in behaviour and voice voice
• Paralytic stage
• Death

Question 13

Dumb rabies

Answer 13

• 10-20% of cases
• Predominantly paralytic
• Lapse into stage of sleepiness
• Death within 3 days

Question 14

What are viriods?

Answer 14

Small, circular, infectious, single stranded RNA molecules that infect plants

Question 15

What are prions?

Answer 15

infectious misfolded proteins that cause spongiform encephalopathy
• Cellular prion (PrPc 253 aa long) localize on the neurons synapses between neurons or facilitate the uptake of copper into the cell
• Caused by the accumulation of the misfolded protein scrapie prion protein (PrPsc)

Question 16

How do prions cause disease?

Answer 16

They cause changes in the shape of normal protein molecules that lead to accumulation of prion protein that then blocks synapses which causes protein degeneration

Question 17

What are some diseases caused by prions?

Answer 17

Mad Cow disease (BSE), Creutzfeldt-Jakob disease, Scrapie, and Kuru