Viruses Ebola Influenza West Nile Virus Rabies HIV
Viruses Ebola Influenza West Nile Virus Rabies HIV
General Characteristics 1. Very small - 10 -1000 nanometers - 10 – 1000 x 10 -9 m - Cannot be seen without an electron microscope
General Characteristics 2. Various Shapes
General Characteristics Protein Coat 3. Structure = Two Parts: Nucleic acid + Protein Coat (Capsid) Nucleic Acid
General Characteristics 4. Acellular - no cell - no organelles - no metabolism - cannot be killed with antibiotics
General Characteristics 5. Nucleic acid - Has DNA - or RNA (retro viruses) DNA - (never both) ? s 1 -6 RNA
General Characteristics § Nucleic Acids § 1. DNA = deoxyribonucleic acid - Double strand - Contains genes for making viral proteins (requires 2 steps)
General Characteristics § Nucleic Acids 2. RNA – ribonucleic acid - Single strand - Retro virus - contains code for directly producing viral proteins
General Characteristics 6. Mutates very easily - no cell - no protection from mutagens E. g. chemicals, radiation, uv light exposure
General Characteristics 7. Virus = Latin for poison
General Characteristics 8. Obligate intercellular Parasite - Cannot reproduce EXCEPT inside a host cell - No metabolism outside host cell - Inside host, uses cell’s reproduction & metabolic mechanisms
General Characteristics 9. Some have an envelope v. Membrane surrounding protein coat v. Made of glycoproteins
Examples of Viruses § § § Common Cold Polio Rabies HIV Hepatitis A, B*, & C Herpes ( E. g. Chicken pox) § Measles § Smallpox § Ebola § Hanta § HPV (Human papilloma virus)* § Mumps § Rubella § Epstein-Barr* § SARS * can cause cancer
Viral Cycles Two Types of Viral Cycles 1. Lytic 2. Lysogenic
Lytic Cycle v 1. 2. 3. 4. Immediate viral replication Viral DNA injected into host cell Viral DNA put into host genome Synthesis & Assembly of virus Cell lysis (rupture) = tissue damage 5. New viruses emerge to infect new cells
Lysogenic Cycle v Viral replication is delayed 1. Viral DNA put into host genome 2. Host cells divide, including viral genes 3. When organism is stressed → → lytic cycle begins → viral replication (cell lysis) etc. ? s 13 -14
Lytic vs Lysogenic Cycle New viruses emerge Viral DNA Bacterial genome STRESS Injection Lysis Assembly Many divisions Synthesis
How do Viruses do Harm? Possible effects: 1. Lyse cells (Tissue damage) 2. Release viral toxins 3. Prevent host’s cell division 4. Disrupt formation of host chromosomes
How do Viruses do Harm? 5. Disrupt lysosomal function 6. Can cause uncontrolled cell division (cancer) 7. Can cause changes in cell membrane (immune system destroys host cells)
Duration of Viral Infections § Acute – rapid onset, death or recovery (most viruses) § Chronic – recurs again & again - latent period = virus dormant between flare-ups E. g. Herpes simplex (cold sores)
Prevention Vaccines v Live or killed virus injected v Host immune system makes antibodies v When infected, host immune system ready to kill virus
Treatment 1. Antiviral drugs Ø Interfere with viral replication Ø E. g. AZT ( for AIDS) Ø E. g. Interferon (for Hepatitis C) 2. Supportive Therapy Ø Reduce fever (E. g. aspirin, Tamiflu) Ø Make host comfortable Ø Wait until virus runs its course ? s 14 -19
Viroids 1. 2. 3. Nucleic acid (RNA) only No protein coat Common in plants
Prions 1. 2. 3. Protein only No nucleic acid Replicate by bumping proteins, causing refolding in shape of prion 4. Cause diseases of nervous system
Prions E. g. v Kreutzfeld-Jakob’s disease Bovine Spongiform Encephalopathy (BSE – a. k. a. Mad cow disease)
Prions 2. Chronic wasting disease Deer and elk
Prions 3. Scrapie – usually fatal sheep disease
Prions 4. Kuru Papua New Guinea Headhunters (cannibalistic tribes) Word to your mama!
Viruses § Are they living or nonliving ? § Are they smart nucleic acids? § Why can’t we kill them? ? s 20 -25
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