Viruses Ebola Influenza Rabies HIV West Nile Virus

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) - (never both) DNA 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 Membrane surrounding protein coat Made of glycoproteins

Examples of Viruses Ebola Hanta HPV (Human papilloma virus)* Mumps 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 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

Lysogenic Cycle Viral replication is delayed Viral DNA put into host genome Host cells divide, including viral genes 3. When organism is stressed → → lytic cycle begins → viral replication (cell lysis) etc.

Lytic vs Lysogenic Cycle New viruses emerge Injection Viral DNA STRESS Bacterial genome Lysis Assembly Many divisions Synthesis

How do Viruses do Harm? Possible effects: Lyse cells (Tissue damage) Release viral toxins Prevent host’s cell division 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 Live or killed virus injected Host immune system makes antibodies When infected, host immune system ready to kill virus

Treatment Antiviral drugs Interfere with viral replication E.g. AZT ( for AIDS) E.g. Interferon (for Hepatitis C) 2. Supportive Therapy Reduce fever (E.g. aspirin, Tamiflu) Make host comfortable Wait until virus runs its course

Viroids Nucleic acid (RNA) only No protein coat Common in plants

Prions Protein only No nucleic acid Replicate by bumping proteins, causing refolding in shape of prion Cause diseases of nervous system

Prions E.g. Kreutzfeld-Jakob’s disease Bovine Spongiform Encephalopathy (BSE) aka 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?