Viruses Chapter 19

What you must know: The components of a virus. The differences between lytic and lysogenic cycles. How viruses can introduce genetic variation into host organisms. Mechanisms that introduce genetic variation into viral populations.

Bacteria vs. Viruses Bacteria Virus _________________ cell Most are free-living (some parasitic) Relatively ________ size __________________ used to kill bacteria Not a living cell (_________ packaged in __________ shell) Intracellular parasite 1/1000 size of bacteria ______________ used to prevent viral infection Antiviral treatment

Viruses Very small (<ribosomes) Components = ____________+ ________ Nucleic acid: DNA or RNA (__________ or __________ -stranded) _____________: protein shell Some viruses also have viral _______________ that surround capsid

Viruses Limited ________ range Entry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal) Eg. human cold virus (rhinovirus)  upper respiratory tract (mouth & nose) _______________ quickly within host cells Can ___________ easily RNA viruses: no error-checking mechanisms

Simplified viral replicative cycle

Viral Reproduction Lytic Cycle: Use host machinery to replicate, assemble, and ___________________________of virus Virulent phages: Cells die through lysis or apoptosis _________________ (Latent) Cycle: DNA incorporated into host DNA and replicated along with it Bacteriophage DNA = prophage Animal virus DNA = provirus UV radiation, chemicals can stimulate: lysogenic  lytic cycle Temperate Phage: uses both methods of replication

Bacteriophage Virus that infects _____________ cells

Lytic Cycle vs. Lysogenic Cycle

Animal viruses have a membranous ___________ Host membrane forms around exiting virus Difficult for host immune system to detect virus

Retrovirus RNA virus that uses ___________________ (RNA  DNA) Newly made viral DNA inserted into chromosome of host (provirus) Host transcribes provirus to make new virus parts Example: ___ (Human Immunodeficiency Virus)

HIV = Retrovirus

HIV Origin: Chimpanzee virus Infects white blood cells (_________________) _______: provirus (DNA inserted), latent _______: <200 WBC count, opportunistic infections

Other Human Viruses __________ virus ______________ Herpes Simplex Virus 1 (HSV-1) Herpes Simplex Virus 2 (HSV-2) Eradicated in 1979 due to worldwide vaccination campaigns

Emerging Viruses = mutation of existing viruses Pandemic: ____________ epidemic

Current Outbreaks ___________ Virus Dengue Fever Chikungunya Spread by Aedes mosquitoes (Aedes aegypti) Major outbreak in Brazil and Latin America Linked to birth defects (microcephaly) Dengue Fever Chikungunya

Drugs for Prevention/Treatment ______________: weakened virus or part of pathogen that triggers immune system response to prevent infection Ex. HPV, MMR, HepA, Flu shot ________________ Drugs: block viral replication after infection Ex. Tamiflu (influenza), AZT (HIV)

Viroids Small, circular _________ molecules that infect __________ Cause errors in regulatory systems that control plant growth Eg. coconut palms in Philippines

Prions Misfolded, infectious ______________ that cause misfolding of normal proteins Eg. scrapie (sheep), mad cow disease (BSE), Creutzfeldt-Jakob disease (humans), kuru (humans – New Guinea)

Diseases caused by prions Prions act slowly – incubation period of at least 10 years before symptoms develop Prions are virtually indestructible (cannot be denatured by heating) No known cure for prion diseases Kuru in New Guinea

Prion Neurodegenerative Diseases Alzheimer’s Disease Parkinson’s Disease