2. Intro to Viruses

Question 1

What is a virus?

Answer 1

Infectious agent that is not cellular and cannot reproduce by itself

Question 2

What are some examples of the giant virus?

Answer 2

• Isolated from amoeba

- Mimivirus, megavirus, pandoravirus

Question 3

What is the tobacco mosaic virus?

Answer 3

• First virus observed under electron microscope

- RNA is the infectious component

Question 4

What is the size properties of viruses?

Answer 4

• small, usually range in size from 20 - 300 nm

Question 5

What is a virion?

Answer 5

Viruses are infectious particles of nucleus acid and protein

• The complete infectious particle is known as a virion
• Contains nuclei acid genome
• Nucleotides
• Protein coat : capsid
• Sometimes a lipid envelope and enzymes

Question 6

How is the genome replicated in the host cell?

Answer 6

• RNA/DNA acts as the genome or template encoding for at least 4 proteins (1 for the coat, 2 for replication and 1 for intercellular movement)

Question 7

How do retroviruses replicate their genome?

Answer 7

Retroviruses package a reverse transcriptase enzyme

• RNA is reverse transcribed into DNA
• DNA then inserts into host genome

Error prone process with a high mutation rate

Question 8

What is the protein capsid constructed from?

Answer 8

Protein subunits

Question 9

What are the different types of self assembly of the protein capsid?

Answer 9

• Helical array (tobacco mosaic virus)
• Icosahedral
• Complex (bacteriophage)
• Other brick like, worm like, bullet shaped

Question 10

What is the replication process of the virus?

Answer 10

• Absorption of phage host cell
• entry of phage nucleic acid
• Phage proteins are synthesised and genetic material is replicated, the host chromosome then degraded
• Assembly of phage within host cell
• Lysis of host cell
• Release of free phage

Question 11

What are the 2 particles of the influenza virus?

Answer 11

H and N particles

• Hemagglutinin enables the virus to enter the cell
• Neuraminidase enables the virus to leave the cell

Question 12

How do new flu strains emerge?

Answer 12

• Different versions of H and N in different virus strains
• Each flu virus carries one gene for H and another for N
• Genes are on separate pieces of RNA (8 genes in flu virus)
• 2 different strains of flu infecting one host cell can exchange versions of H and N to make new combos which the immune system cannot recognise new combinations

Question 13

What are the chemical treatments?

Answer 13

• Relenza
• Tamiful
• Both are neuraminidase inhibitors that prevent flu virus from exiting used host cells

Question 14

How is SARS spread?

Answer 14

Spread throughout the world through air travel

• Spread in sputum, faeces
• Virus remains viable for several days on dry surfaces

Question 15

What is a viriod?

Answer 15

• Single circular strand of naked RNA
• Particles are 1/1000 the size of a virion
• 246-380 nucleotides of ssRNA which is not enough to encode a protein

Question 16

What are prions and some examples of the disease they cause?

Answer 16

Infectious proteins

- Cause BSE or mad cow disease, sheep scrapie, C-Jakob disease and kuru in humans

Question 17

What is the mechanism of action for prion infection?

Answer 17

• PrP is the normal brain prion protein
• Converted to PrP^Sc
• PrP^Sc when mixed with PrP will cause the PrP to convert to PrP^Sc (chain reaction)

Question 18

What happens if we eat PrPSc?

Answer 18

• It spontaneously converts our PrP to PrPSc

- PrPSc forms insoluble plaques in brain disease

Question 19

What causes Mad Cow disease?

Answer 19

• Cattle were fed ground up bodies of sheep and other cows
• Bodies contained some PrPSc
• Caused conversion of PrP to PrPSc which caused disease (spongiform encephalitis)
• People ate the brains/CNS of cows, which induced CJD