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. vs. Viruses

Bacteria Virus  Prokaryotic  Not a living cell (genes  Most are free-living (some packaged in protein shell) parasitic)  Intracellular parasite  Relatively large size  1/1000 size of bacteria  Antibiotics used to kill  Vaccines used to prevent bacteria viral infection  Antiviral treatment Viruses

 Very small (

 Limited host 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)  Reproduce quickly within host cells  Can mutate easily ◦ RNA viruses: no error-checking mechanisms

Simplified viral replicative cycle Entry: Injection endocytosis, fusion VIDEO: T4 PHAGE INFECTION

 Virus that infects bacterial cells Viral Reproduction - phages

 Lytic Cycle: ◦ Use host machinery to replicate, assemble, and release copies of virus ◦ Virulent phages: Cells die through lysis or apoptosis  Lysogenic (Latent) Cycle: ◦ DNA incorporated into host DNA and replicated along with it ◦ Bacteriophage DNA = prophage ◦ Animal virus DNA = ◦ UV radiation, chemicals: lysogenic  lytic cycle ◦ Temperate Phage: uses both methods of replication Lytic Cycle of T4 Phage Lytic Cycle vs. Lysogenic Cycle Animal viruses have a membranous envelope

 Host membrane forms around exiting virus  Difficult for host immune system to Viral RNA polymerase detect virus VIDEO: HOW DENGUE VIRUS ENTERS A CELL VIDEO: HIV LIFE CYCLE

 RNA virus that uses (RNA  DNA)  Newly made viral DNA inserted into chromosome of host (provirus) ◦ *provirus never leaves the host genome  Host transcribes provirus to make new virus parts  Example: HIV (Human Immunodeficiency Virus) HIV = Retrovirus HIV ◦ Origin: Chimpanzee virus ◦ Infects white blood cells (helper T) ◦ HIV+: provirus (DNA inserted), latent ◦ AIDS: <200 WBC count, opportunistic infections Other Human Viruses

 Herpes virus  Smallpox

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: global epidemic Current Outbreaks

 Zika Virus ◦ Spread by Aedes mosquitoes (Aedes aegypti) ◦ Major outbreak in Brazil and Latin America ◦ Linked to birth defects (microcephaly)  Dengue Fever  Chikungunya ZikaVirus (as of Dec. 2015) Drugs for Prevention/Treatment

 Vaccine: weakened virus or part of pathogen that triggers immune system response to prevent infection ◦ Ex. HPV, MMR, HepA, Flu shot  Antiviral Drugs: block viral replication after infection ◦ Ex. Tamiflu (influenza), AZT (HIV) Viroids

 Small, circular RNA molecules that infect plants  Cause errors in regulatory systems that control plant growth  Eg. coconut palms in Philippines Prions

 Misfolded, infectious proteins 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 Prions

 Video AMOEBA SISTERS: VIRUSES: VIRUS REPLICATION AND THE MYSTERIOUS COMMON COLD TED-ED: HOW WE CONQUERED THE DEADLY SMALLPOX VIRUS