Pathogens . . . They’ve Gone Viral !!!

Pathogens . . . They’ve Gone Viral !!! Part One Applied Ag Biology

Whatis a Virus? • Segments of nucleic acids contained in a protein coat • Smaller than bacteria • Only seen w/ electron microscope • Replicate by infecting cell & using that cell to make more viruses

Is a Virus a Living Organism? • NO!!! Biologists don’t consider them to be alive. • They do not have all properties of life – no metabolism, no homeostasis, no growth • They DO cause diseases in living organisms

Discovery of Viruses • In late 1800’s, scientists were trying to determine cause of Tobacco Mosaic Disease • Disease was caused by something smaller than a bacteria • Called the agent a VIRUS, the Latin word for poison • Assumed to be tiny cells

Discovery of Viruses • In 1935, tobaccomosaic virus (TMV) waspurified • Had a crystal structure, whichis a property of chemicals • Its structure allowedit to infect healthytobacco plants • Conclusion = TMV was a chemical, not an organism

Virus’s Shape Determined by Its Parts • Capsid = the virus protein coat; contains DNA or RNA (not both) • Examples of DNA viruses: warts, chickenpox, mononucleosis • Examples of RNA viruses: HIV, influenza, rabies

Most Viruses Have an Envelope • Envelope = membrane which surrounds capsid in many viruses; helps virus enter cells

Common Shape of Viruses 1. Helical – rod-like in appearance, with capsid proteins winding around the core in a spiral Ebola Virus

Common Shape of Viruses 2. Polyhedral – many sides and is roughly spherical

How Do VirusesReplicate? • Lack enzymes needed for metabolism • No structures to make proteins • Rely on living hosts to replicate • Step 1 – Virus infects host cell. • Step 2 – Virus either go into the LYTIC CYCLE or LYSOGENIC CYCLE

Lytic Cycle • Lytic Cycle: the cycle of viral infection, replication, and cell destruction • Viruses cause damage when they replicate inside cells • Virus replicats 100’s of times and breaks out – destroying cell

Lysogenic Cycle • During infection, some viruses stay inside cells but don’t make new viruses • Lysogenic Cycle: cycle in which the viral genes replicate without destroying host cell

Lysogenic Cycle • In animal cells, virusesreplicateslowlyso host cellis not destroyed • Example: virus that causes cold sores hidesdeep in the nerves of the face; when body becomesstressed, the virus begins to cause tissue damage (cold sore/fever blister)

Pathogens . . . They’ve Gone Viral !!!