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