Viruses
• What are viruses?• Structure• Infection &Replication• Examples• Viroids• Prions
The envelope contains rigid "spikes" of haemagglutininand neuraminidase which form a characteristic halo of projections around negatively stained virus particles.
What are viruses?• Living or non-living• Intracellular
parasites?• No membranes,
ribosomes, energy production
• Can only reproduce inside a host cell
• Size of Virus• Host specific
Structure
• Many different sizes and shapes
• 0.05-0.2 microns in diameter
• Has hereditary material
Structure• Hereditary material: • DNA or RNA• Single stranded/
double stranded• Linear or circular• Protein coat:• Simple or complex• Envelope:• Lipid membrane
Examples
Influenza single stranded RNA
Herpes Double stranded DNA
Infection &Replication
• Host specific• Can be tissue or cell
specific
Sequence of Viral infection
• Penetration- inject hereditary material or engulfed by the cell & then release of genetic material into the cell
• Replication- copy the genetic material• Protein synthesis- viral proteins are made• Assembly- viral genetic material and
enzymes surrounded by protein coat• Release- lysis (cell bursting) or “budding”
of viral particles
HIV retrovirus
Herpes Virus
ExamplesRabies Polio
Ebola
Small pox
Treatment of Viruses
• Intracellular: antibiotics ineffective• Anti-virals: can kill host cells• Block replication or assembly
Viroids & Prions• Viroids- lack a protein
coat• Prions- Protein infectious
agent• 1982- Stanley Prusiner
found evidence of proteins
• Protein causes folding of normal proteins
• Kuru, Creutzfeldt-Jakob and bovine spongiform encephalopathy
• Mad Cow disease