Lecture 7

Question 1

polio, meningitis, hepatitis, and the common cold are all members of which virus family?

Answer 1

Picornaviruses

Question 2

Describe the picornavirus (physical properties)

Answer 2

• small
• (+) stranded RNA
• naked (non-enveloped)
• icosahedral capsid

Question 3

Where do picornaviruses replicate?

Answer 3

The cytoplasm

Question 4

What viruses causes the majority of common colds?

Answer 4

Human rhinovirus

Question 5

What does it mean that “Rhinoviruses are thermo- and acid-labile”

Answer 5

They replicate in the upper respiratory tract where the temperature is lower than body temp (37) and they also don’t survive in the stomach

Question 6

Why do you get repeated infection of the cold?

Answer 6

Bc its caused usually by Rhinovirus which has 150 different stereotypes

Question 7

How many different capsid proteins does rhino virus have?

Answer 7

4

Question 8

What at the end of rhinovirus ss + RNA serves as a primer?

Answer 8

There is a tyrosine molecule that serves as a primer = VGP

Question 9

What type of genome is picornavirus

Answer 9

ss + RNA

Question 10

What allows for direct translation of the picornavirus genome?

Answer 10

The internal ribosomal entry site (IRES) in the 5’ end of the genome allows direct translation of the genome into a polyprotein

Question 11

How does the Picornavirus shut down translation of host proteins?

Answer 11

○ 2A protease cleaves EIF-4G
- EIF-4G = cap binding protein, it binds to methyl-7 guanosine caps on cellular messenger RNA. Recruits those RNA’s to the small 40s ribosomal subunit. Then the ribosome looks for start codon and then recruits the large ribosomal subunit
- But 2A cleaves EIF-4G so now the part that binds the ribosome is disconnected from the part that binds the cap so now cellular mRNAs are no longer recruited so host translation of mRNA stops
- The IRES comes in and enables the poliovirus RNA to undergo ‘cap-independent translation’ so now can bind the small ribosomal subunit directly, it has no requirement for the EIF-4G subunit

Question 12

Influenza A viruses are divided into subtypes based in 2 proteins on the surface of the virus - What are they

Answer 12

Hemagglutinin (H) - 18 subtypes
Neuraminate (N) - 11 subtypes

Question 13

What is the genome of influenza

Answer 13

enveloped virus containing segmented (-) sense RNA genome

Question 14

What is a complication of influenza infection

Answer 14

• Complications = bacterial superinfections, pneumonia, myocarditis and “cytokine storms”
  ○ Uncontrolled immune response, lots of cytokines produced at once leading to shock

Question 15

How do you get many proteins from the same RNA?

Answer 15

Have multiple reading frames - many start codons

Question 16

How does influenza shut down host synthesis?

Answer 16

§ Cap snatching = viral rna pol binds caps of cellular mRNA in nucleus and cleaves off the caps and then the cap serves as the template for the production of + strand RNA

§ Results in degradation of cellular mRNA

§ Viruses also interferes with the mitochondria to interfere with apoptosis

Question 17

How does poliovirus shut down translation of host proteins?

Answer 17

Normally:
- eIF-4G binds caps of cellular mRNA, recruiting small ribosomal subunit, and ribosome scans to look for start codon and recruits the large subunit (starts protein translation)

Poliovirus:
- 2a protease cleaves eIF-4G so cellular mRNAs are no longer brought to small ribosomal subunit for translation (HOST TRANSLATION OF CELLULAR mRNA STOPS!)
- IRES enables poliovirus RNA to undergo cap independent translation, binds to small subunit directly without requiring eIF4g
- this enables poliovirus RNA to be translated but not cellular mRNA