Intro to Viruses

Question 1

Bacteria vs Viruses?

Answer 1

• Bacteria: 1000nm. Viruses: 10-300nm
• Bacteria: DNA/RNA. Viruses: DNA/RNA (never both)
• Bacteria: Extracellular reproduction. Viruses: Intracellular
• Bacteria: Light Microscopy. Viruses: Electron Microscopy

Question 2

Components of a virus?

Answer 2

1. Nucleic Acid
2. Capsid
3. May have an envelope

Question 3

Features of the Capsid?

Answer 3

• Made up of capsomeres.
• Variable shape/symmetry
  
  1. Icosahedral.
  2. Helical
  3. Complex

Question 4

Role of the capsid?

Answer 4

1. Introduces viral genome into the host cell- via interaction with host receptors
2. Stimulates an immune response- via viral antigens
3. Resistance to
   - Heat
   - Drying
   - Acid
   - Proteases
   - Detergents

Question 5

Features of the viral envelope?

Answer 5

• Lipid bilayer
• Contains PPL’s and GP’s
• Derived from host cell membranes
• Allows budding (lysogenic cycle)
• Proteins to help attach to host cells
• Sensitive to heat, drying, acid, proteases, and detergents.

Question 6

What determines Cell tropism?

Answer 6

1. Specific host receptors for the virus
2. Physical barriers
3. Local tempertaure, pH, O2 tension, enzymes, etc.
4. Ability of the cell to recognise and transcribe viral promoter and enhancer nucleic acid sequences
5. Ability of cell to support replication

Question 7

Describe Viral Replication?

Answer 7

1. Attachment to host cell
   
   • Enters via endocytosis or memb. fusion
2. Uncoated
3. Taken to nucleus or cytoplasm for transcription
4. Translated in the cytoplasm
   
   • Viral proteins made
5. New viruses released
   - Exocytosis/Lysis
   - or budding