Viruses Section 2.2 Nelson 11 Biology Pages 54-59

Viruses  Small, non-living particles  Genetic material surrounded by a protein capsule, called a capsid.

Viruses

Reproductive material DNA or RNA Virus inserts its genetic material into a host cell, the DNA or RNA takes control of the host cell causing the cell to make copies of the viral DNA or RNA

Why viruses are important Cause human disease Easily spread from person to person Epidemic-in one geographic area Pandemic-global scale Can lead to some types of cancers Crop destruction

Classification 4000 viruses have been classified Potentially, millions of viruses exist

Characteristics

Infectious Cycles

Lysogenic Cycle Viral DNA can stay dormant for many years Bacterium continues to grow and divide normally, making copies of DNA that the virus inserted in it Changes in the cell environment cause viral DNA to become active

Lytic cycle Lysis occurs as the cell ruptures releasing new viruses into the host cell’s surroundings. Host cell is destroyed One hour

Vaccinations Mixtures contain weakened forms or parts of a dangerous virus Trigger immune response without infection Immune system remembers virus and quickly responds to future encounters with virus

HPV Human papillomavirus 2006 Causes 70% of cervical cancer cases

Hard Cases AIDS virus very complex Influenza changes to frequently

Gene therapy Using virus to deliver repairs (drugs or genes) to cells. Examples: Target cancer cells with drugs Repair genetic disorders Genetically modified organisms

Viroids and Prions Viroids: small infectious pieces of RNA Highly destructive plant pathogens Prions: proteinaceous infectious particles Cause rare diseases in mammals (mad cow disease)