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Chapter 18, Section 2 Viruses Virus • Non-living strand of genetic material with a protein coat • No organelles • Do not move • Cannot replicate on their own • Size: 5 – 300 nm (nanometers – about 1 billionth of a meter) Viral Diseases • • • • • • • • AIDS Herpes Measles, Mumps, Chicken Pox Cold, Influenza Warts, Shingles Gastroenteritis Polio, viral meningitis, rabies Small Pox, Hepatitis Where did viruses come from? • Possibly parts of cells – Genetic material of viruses is similar to that of cells Virus Structure • Covered by an outer layer of proteins called a capsid • Inside the capsid – genetic material – could be DNA or RNA Viral Infections • To replicate, viruses must infect host cells – Two types of infections • Lysogenic • Lytic Lysogenic Cycle • Viral DNA enters nucleus of host cell • DNA stays dormant • Under the right conditions, the viral DNA is activated and the Lytic Cycle begins Lytic Cycle • Host cell makes copies of viral DNA or RNA • Invading genetic material instructs the host cell to make more viral protein capsids and enzymes needed for viral replication • New viruses start to form • Host cell explodes and releases the new viruses http://www.geocities.com/madokagm/BIOL1551/lecture_notes_Nov_22_files/image002.jpg Virus Rejects • Retrovirus – Has RNA instead of DNA – Ex HIV Virus • Prions – Proteins that can cause infectious diseases – Prions exist in cells, but mutations cause the prions to be incorrectly folded – can cause normal proteins to mutate – Mad Cow Disease, Creutzfeldt-Jakob Disease How much do you know? • Which cycle causes the host cell to burst? • What is the difference between a virus and a retrovirus? • What type of virus is HIV? • Do prions have genetic material? • Are viruses living? Give one reason why or why not? • Are viruses bigger or smaller than normal cells?
