Viruses General Characteristics
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Viruses General Characteristics Ebola Influenza West Nile Virus Rabies HIV General Characteristics 2. Various 1.Very small - 10 -1000 nanometers - 10 – 1000 x 10 -9 m - Cannot be seen without an electron microscope General Characteristics Shapes Protein Coat 3. Structure = Two Parts: Nucleic Acid Nucleic acid + Protein Coat (Capsid) 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 11-6 RNA 1 General Characteristics General Characteristics Nucleic Acids 1. DNA = deoxyribonucleic acid - Double strand - Contains genes for making viral proteins (requires 2 steps) Nucleic Acids 2. RNA – ribonucleic acid - Single strand - Retro virus - contains code for directly producing viral proteins General Characteristics General Characteristics 6. Mutates very easily - no cell - no protection from mutagens E.g. chemicals, radiation, uv light exposure 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’ cell’s reproduction & metabolic mechanisms General Characteristics 9. Some have an envelope Membrane surrounding protein coat Made of glycoproteins 2 Examples of Viruses Common Cold Polio Rabies HIV Hepatitis A,B* A,B*,& C Herpes ( E.g. Chicken pox) Measles Smallpox ?s 88-11 Ebola Hanta HPV (Human papilloma virus)* virus)* Mumps Rubella EpsteinEpstein-Barr* Barr* SARS Two Types of Viral Cycles 1. Lytic 2. Lysogenic * can cause cancer Lytic Cycle 1. 2. 3. 4. 5. Viral Cycles Lysogenic Cycle Immediate viral replication Viral DNA injected into host cell Viral DNA put into host genome Synthesis & Assembly of virus Cell lysis (rupture) = tissue damage New viruses emerge to infect new cells Lytic vs Lysogenic Cycle New viruses emerge Viral DNA Bacterial genome STRESS Injection Lysis Assembly Many divisions 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) lysis) etc. How do Viruses do Harm? Possible effects: 1. Lyse cells (Tissue damage) 2. Release viral toxins 3. Prevent host’ host’s cell division 4. Disrupt formation of host chromosomes Synthesis 3 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) Prevention Vaccines Live or killed virus injected Host immune system makes antibodies When infected, host immune system ready to kill virus Viroids 1. Nucleic acid (RNA) only 2. No protein coat 3. Common in plants Duration of Viral Infections Acute – rapid onset, death or recovery (most viruses) Chronic – recurs again & again - latent period = virus dormant between flareflare-ups E.g. Herpes simplex (cold sores) Treatment 1. Antiviral drugs ¾ Interfere with viral replication ¾ E.g. AZT ( for AIDS) ¾ E.g. Interferon (for Hepatitis C) 2. Supportive Therapy ¾ Reduce fever (E.g. aspirin, Tamiflu) Tamiflu) ¾ Make host comfortable ¾ Wait until virus runs its course ?s 1313-16 Prions 1. Protein only 2. No nucleic acid 3. Replicate by bumping proteins, causing refolding in shape of prion 4. Cause diseases of nervous system 4 Prions E.g. KreutzfeldKreutzfeld-Jakob’ Jakob’s disease Bovine Spongiform Encephalopathy (BSE – a.k.a. Mad cow disease) Prions 3. Scrapie – usually fatal sheep disease Prions 2. Chronic wasting disease Deer and elk 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’ can’t we kill them? ?s 1717-25 5
