Introduction to viruses

Question 1

Explain why viruses are ribosomal parasites

Answer 1

Viruses are ribosomal parasites bc they have their own RNA however, in order to generate mRNA/translate that into viral proteins, it requires the host reproductive machinery. Alone viruses are unable to replicate

Question 2

Illustrate or describe the basic step in the life cycle of a gneric virus

Answer 2

Infecting virus

attachment

penetration

uncoating

replication => sythnesis of viral mRNA (direct or via host machinery), synthesis of viral protein for new capsids, synthesis of viral nucleic acid

assembly => capsids form around nucleic acid

release

Question 3

Define the *key* terms with respect to virsuses and infections

Answer 3

Susceptible: Has receptor which virus can bind to

Resistant: Does not have receptor for virus to bind to

Permissive: Enables viral replication/reproduction

Susceptible and permissive: allows the entire viral infectious cycle to take place

Question 4

Explain the importance of the cellular receptor used by a virus and the relationship between virus receptors and virus diseases

Answer 4

The host cell receptor viruses target in order to enter the cell dictate the species/tissue/cell tropism (infectivity) of the virus and therefore the pathology of the virus

adenovirus

picornavirus

Alterations in the affinity of the virus for a particular host cell receptor or co-receptor can alter the virus tropism

Influenza

HIV-1

Question 5

List all of the mechanisms of virus entry and penetration

Answer 5

Penetration

• phagocytosis
• endocytosis

–> pinocytosis & receptor mediated endocytosis

Question 6

What are the 3 types of mechanisms used for penetration and uncoating?

Answer 6

Uncoating at the plasma membrane

Uncoating within endosomes

Uncoating at the nuclear membrane

Question 7

Adenovirus entry and uncoating

Answer 7

receptor mediated endocytosis

uncoating within the endosome