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Delve into the fascinating realm of viruses, exploring their structure, replication mechanisms, and impact on living organisms. Discover the difference between lytic and lysogenic cycles and the varied shapes of viral particles. Unravel the mysteries of these tiny entities that have the power to cause diseases and shape biological ecosystems.
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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)
