Virus,Viroids and Prions

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Reported By: Klark Yeysen D. Macarasig

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Wendell Stanley (1935)crystallized sap from sick tobaccoplants. He discovered viruses

were made of nucleic acid andprotein

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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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