L13- Virus-host cell interactions

Question 1

What are key facts about viruses?

Answer 1

• Size < 300nm
• Cannot be grown on artificial culture media
• Replication only occurs within living cells
• Obligate, intracellular parasites
• Viruses only contain nucleic acid and protein
• Either DNA or RNA genome, single or double

Question 2

What are the different types of viruses?

Answer 2

• Herpes simplex virus type 1 and 2- cold sores and genital herpes
• Papilloma viruses- warts and cervical cancer
• Polioviruses- asymptomatic or paralysis
• Influenza virus
• HIV-1- AIDS

Question 3

What is an icosahedron?

Answer 3

• Regular geometric figure constructed from 20 equilateral triangles
• Shape of most viral nucleocapsids

Question 4

How are viral envelopes constructed?

Answer 4

• Derived from membranes of host cells but modified to contain virus-specific glycoproteins

Question 5

What are the steps in the virus replication cycle?

Answer 5

1. Attachment to surface of the host cell using virus receptors on cell surfaces
2. Virus enters host cell by penetration
3. Uncoating occurs where viral envelope and capsid is shed
4. Replication- synthesis of viral mRNA (direct or via host machinery), synthesis of viral protein for capsid, synthesis of viral nucleic acid
5. Assembly of capsids form around nucleic acid.

Question 6

What type of RNA can act as mRNA for viruses?

Answer 6

Positive sense RNA

Proteins can be translated from this

Question 7

What does an imbalanced ratio of RNA+ to RNA- do?

Answer 7

Causes inhibition of host cell protein synthesis

Question 8

What are the changes in host cell found after virus infection?

Answer 8

• Lytic effect- kills host cell after replication
• Fusion- syncytium (joining of several infectied cells to form large clumps)
• Cell transformation and malignancy- some viruses carry oncogenes