1 - Place and significance of viruses in the biosphere, evolution of viruses.

Question 1

History

Answer 1

• Correlation between diseases and bacteria
  
  • Tobacco Mosaic Disease agent:
    
    • Transmission through bacteria-proof filters
  • Foot and mouth disease:
    
    • No bacteria under the microscop e→ Toxins (i.e. Viruses)
• Electron microscopes – Virus independent of bacteria

Question 2

Morphology

Answer 2

• 2 forms of existence:
  
  1. Viron:
     
     • ​Infectous particle outside the body
     • Show no live activity outside cell – just transfers genetic info from cell-to-cell
     • Contain:
       
       • Nucleic acid (DNA or RNA)
       • Proteins
       • Lipids - forms membranes on surface “envelope”
  2. Vegetiative virus​
     
     • ​​The infected cell

Question 3

Reproduction

Answer 3

• Multiplication is very effective
• Few organelles (no mitochondria etc.)
• No energy production, protein synthesis enzymes and no NA enzymes

Question 4

Occurence

Answer 4

• Widespread
• Infect bacteria, fungi, plants, animals and humans

Question 5

Significance

Answer 5

• Pathogens of animals/humans
• Human pathogens
• Emerging new viruses
  
  • Influenza
  • Ebola
  • HIV
• Simple living creatures, but a threat to the human race
• Protection: immunization
• Orphan viruses: no-pathogenic, do not cause disease
• Viruses are parts of the biosphere

Question 6

When can viruses be useful?

Answer 6

• Placenta development
• Biotechnology: gene therapy (vectors)
• Viral proteins: potential medicines

Question 7

Origin

Answer 7

• Simplest but not the most ancient of life forms
• Most viruses of eukaryotes probably have been evolved from prokaryotic viruses (bacteriophages)
• Very diverse origin
• Do not fit into phylogenetic tree of living creatures

Question 8

Theories

Answer 8

1. Gell degeneation: parasite cell lost its independence
2. Runaway cell compnents (with gentic information):
   
   • mRNA → +ssRNA virus
   • Chormosome fragment - dsDNA virus
   • ssDNA, dsRNA, ssRNA

ss: single stranded
ds: double stranded