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DO NOW 1. Label the following as Totipotent, Multipotent, or Pluripotent A. B. C. D. Embryonic Stem Cells Bone Marrow Cells Umbilical Cord Stem Cells Zygote 2. During what embryonic phase do cells differentiate? 3. What is the role of morphogens in embryo development? Viruses Chapter 19.4 What to Know about Viruses? Characteristics Structure How they reproduce: 1. 2. 3. ◦ 4. The differences between lytic and lysogenic cycles. How we think they evolved Bacteria vs. Viruses Bacteria Virus Prokaryotic cell Most are free-living (some parasitic) Not a living cell (genes packaged in protein shell) Intracellular parasite Relatively large size 1/1000 size of bacteria Antibiotics used to kill bacteria Vaccines used to prevent viral infection Antiviral treatment Root Words “phage” – Virus Host – what the virus infects Virus Characteristics 1. 2. 3. 4. 5. 6. Not made of cells Depend on other hosts (other living things) for life functions, such as reproduction & metabolism Transmit DNA to other organisms Infect all life forms (prokaryotes & eukaryotes) Evolve independently of other organisms Cause most diseases Structure of Virus 1. Nucleic acid: DNA or RNA (double or singlestranded) 2. Capsid: protein shell bacteriophage Some viruses also have viral envelopes that surround capsid Simplified viral replicative cycle VIRAL REPRODUCTION Virulent: active Lysogenic: inactive Bacteriophage Reproduction 1. Lytic Cycle: ◦ Virulent Phage reproduction ◦ Uses host cell to make more of itself ◦ Kills host cell by lysing (rupturing) & releasing new viruses 2. Lysogenic Cycle: ◦ Lysogenic Phage reproduction ◦ Prophage (Viral DNA) is incorporated into host’s DNA and replicated along with it Temperate Phage: uses both methods of replication VIDEO: T4 PHAGE INFECTION Lytic Cycle vs. Lysogenic Cycle Animal viruses have a membranous envelope Host membrane forms around exiting virus Difficult for host immune system to detect virus VIRAL INFECTIONS Bacteriophage Virus that infects bacterial cells Retrovirus RNA virus that uses reverse transcriptase (RNA DNA) Newly made viral DNA inserted into chromosome of host Host transcribes viral DNA (“provirus”) to make new virus parts Example: HIV (Human Immunodeficiency Virus) HIV ◦ Infects white blood cells ◦ HIV+: provirus (DNA inserted) ◦ AIDS: active viral reproduction VIDEO: HIV LIFE CYCLE HIV = Retrovirus Herpes virus Smallpox Herpes Simplex Virus 1 (HSV-1) Herpes Simplex Virus 2 (HSV-2) Eradicated in 1979 due to worldwide vaccination campaigns VACCINES Vaccines Consists of a weakened virus or part of pathogen that triggers immune system response Emerging viruses = mutation of existing viruses Prions Misfolded, infectious proteins that cause misfolding of normal proteins Eg. mad cow disease (BSE),CreutzfeldtJakob disease (humans), scrapie (sheep) VIRUS EVOLUTION Where did they come from? Viral Evolution Viruses evolved many times from many different cell (host) groups 1) Some are probably derived from escaped genetic materials 2) Some probably evolved from highly reduced parasites EXIT QUIZ 1. 2. 3. 4. What are the 2 common parts that all viruses have? What is the overall outcome of a Lysogenic Cycle? What is the overall outcome of a Lytic Cycle? Why do people have to get a flu shot every year? Viroids Small, circular RNA molecules that infect plants Cause errors in regulatory systems that control plant growth Eg. coconut palms in Philippines 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