5 - Morphology of viruses

Question 1

What is a viron composed of?

Answer 1

• Core
  
  • Nucleic acid and proteins
• Capsid
  
  • Proteins
• Envelope (may/may not be enveloped)
  
  • Lipid membrane and proteins

Question 2

Examination

Answer 2

1. Electron microscopy, ultra thin sections
2. Negative contrast staining, uranyl acetate
3. Shadow casting = 3D structure

Question 3

What is the morphology determined by?

Answer 3

Capsid

Question 4

1. What is the capsid composed of?
2. Types of capsid

Answer 4

• Capsid is composed of protein units named capsomers
• Types:
  1. Helical:
     
     • Capsomer + nucleic acid = nucleocapsid (no animal pathogens)
  2. Quasihelical
     
     • ​Othomyxo
     • Paramyxo
     • Rhabdovirus
     • Always enveloped
  3. Icosahedreal (cubic)
     
     • ​20 equilateral triangles
     • Proteins arranged in capsomers
     • Adenovirus, parvovirus
     • May have envelopes (herpes, flavivirus)
  4. Binal
     
     • ​Icosahedral head + helical tail
     • Tailed bacteriophages
  5. Complex
     
     • ​Poxvirus
     • No capsomers
     • Complicated symmetry
  6. Pleomorphic
     
     • ​Arenavirus, G type phages
     • No capsid
     • Always enveloped

Question 5

Virus classification by genome structure and core

Answer 5