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8/10/2019 Virus,Viroids and Prions
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Reported By: Klark Yeysen D. Macarasig
8/10/2019 Virus,Viroids and Prions
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Wendell Stanley (1935)crystallized sap from sick tobaccoplants. He discovered viruses
were made of nucleic acid andprotein
8/10/2019 Virus,Viroids and Prions
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Some viruses are enclosed in anprotective envelopeSome viruses may have spikes to helpattach to the host cell
Most viruses infect only specific hostcells
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Viral capsids (coats) are made ofindividual protein subunits
Individual subunits are calledcapsomeres
Use the raw materials and enzymes ofthe host cell to be able to reproduce
Outside of host cells, viruses areinactive
Virus-free cells are rare
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Viruses come in a variety of shapes:
Some may be helical shape like theEbola virus
Some may be polyhedral shapeslike the influenza virus
Others have more complex shapes like bacteriophages
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Helical Viruses
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Polyhedral Viruses
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LYTIC CYCLE1. Attachment to the cell2. Penetration (injection) of viral
DNA or RNA3. Replication (Biosynthesis) of new
viral proteins and nucleic acids4. Assembly (Maturation) of the new
viruses5. Release of the new viruses into
the environment (cell lyses)
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LYSOGENIC CYLEPhage DNA injected into host cellViral DNA joins host DNA forming a
prophageWhen an activation signal occurs, thephage DNA starts replicatingViral DNA (part of prophage) maystay inactive in host cell for longperiods of timeReplicated during each binary fissionOver time, many cells formcontaining the prophages
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Some viruses have the ability tobecome dormant inside the cell calledlatent viruses
They may remain inactive for longperiods of time (years)
Later, they activate to produce new
viruses in response to some externalsignal
HIV and Herpes viruses are examples
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When a virus enters a host cell, thehost antibodies are produced
An interaction between antibodies andvirus’ should inactivate the virus
Some viruses escape antibodies andare able to change their surfaceproteins
Surface proteins are called spikes
This is why you can get the flumany different times
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•
Viroids are Small, circular RNAmolecules without a protein coat• They cause plant diseases•
They can interfere with the metabolismof plant and stunt the growth of plants,sometimes killing the plants in theprocess.
• Occur mainly in warm climates andcause loss of profit as the causativeagents of the potato disease or the
Cadang-Cadang disease of palms.
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•
Was the first viroid to be identified• Infected potato plants appear erect ,
spindly , and dwarfed
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•
A lethal viroid of Coconut .• Cadang-cadang literally means 'dying
dying' in Bicol.
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•
Is a disease of citrus plants• It can causes stunted growth and
reduced yields in affected plants.• The disease is also sometimes called
"scalybutt "
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•
Prions are “ infectious proteins ” • A small proteinaceous infectious
disease-causing agent that is
believed to be the smallestinfectious particle.• All known prion diseases affect
the structure of the brain orother neural tissue , and all arecurrently untreatable and arealways fatal .
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• Also known as prion diseases .• Group of progressive
conditions that affectthe brain and nervoussystem of animals and humans
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Mad Cow Disease
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