VirusesVirusesLiving or NotLiving or Not

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Characteristics of Characteristics of VirusesViruses

Among the Among the smallest biological smallest biological particles that are particles that are capable of causing capable of causing diseases in living diseases in living organismsorganisms

Constructed of Constructed of compounds compounds associated with associated with cellscells

Not Considered LivingNot Considered Living A virus is not a A virus is not a

bacteria, fungus, bacteria, fungus, protist, plant or protist, plant or animal.animal.

They can not carry They can not carry out cellular out cellular functions.functions.

A virus can not A virus can not replicate without replicate without infecting cells and infecting cells and then using the then using the organelles and organelles and enzymes of the cells enzymes of the cells of the host.of the host.

A Virus Has Two Essential A Virus Has Two Essential FeaturesFeatures

A Nucleic AcidA Nucleic Acid DNA orDNA or RNARNA But not bothBut not both

A Capsid – a A Capsid – a protein coat protein coat surrounding surrounding the nucleic the nucleic acid.acid.

Some may have Some may have a membrane a membrane like structure like structure outside the outside the capsid called capsid called an envelopan envelop Examples:Examples:

InfluenzaInfluenza ChickenpoxChickenpox Herpes-simplexHerpes-simplex HIVHIV

Viral ShapeViral Shape The shape of the virus The shape of the virus

is determined by is determined by either its capsid or its either its capsid or its nucleic acidnucleic acid

Two examples of shapeTwo examples of shape Icosahedron has 20 Icosahedron has 20

trianglular faces -- trianglular faces -- herpes simplex, chicken herpes simplex, chicken pox and poliopox and polio

Helix is a spiral shapeHelix is a spiral shape ( like DNA) -- rabies, ( like DNA) -- rabies,

measles and tobacco measles and tobacco mosaic virusmosaic virus

There are Two Types of There are Two Types of VirusesViruses

DNADNAReplicated in one of two Replicated in one of two wayswaysDirectly produce RNA that Directly produce RNA that make new viral proteinsmake new viral proteins

Join with the host cell’s DNA Join with the host cell’s DNA to produce new viral proteinsto produce new viral proteins

RNARNA Viral RNA is released into the host Viral RNA is released into the host

cell’s cytoplasm and uses the cell’s cytoplasm and uses the ribosomes to produce new viral ribosomes to produce new viral proteinsproteins

Some are known as retroviruses Some are known as retroviruses containing an enzyme called containing an enzyme called reverse transcriptase. These use . These use the RNA as a template to make the RNA as a template to make DNA. This DNA is integrated into DNA. This DNA is integrated into the host cell’s DNAthe host cell’s DNA..

ViroidViroid

Smallest known particles able to Smallest known particles able to replicatereplicate

Short single strand of RNAShort single strand of RNA No capsidNo capsid Disrupts plant metabolism and may Disrupts plant metabolism and may

damage an entire cropdamage an entire crop

PrionsPrions

Abnormal forms of proteins that Abnormal forms of proteins that clump in cellsclump in cells

Linked to diseases of the brainLinked to diseases of the brain Consist of 250 amino acids and Consist of 250 amino acids and

not associated with any nucleic not associated with any nucleic acidacid

Examples:Examples: Scrapies in sheepScrapies in sheep Mad Cow Disease in cattleMad Cow Disease in cattle

                                                 

                       

What is Mad Cow DiseaseWhat is Mad Cow Disease

Mad cow diseaseMad cow disease, or , or bovine spongiform bovine spongiform encephalopathyencephalopathy (BSE), is a fatal brain (BSE), is a fatal brain disorder that occurs in cattle and is caused by disorder that occurs in cattle and is caused by some unknown agent. some unknown agent.

Brain cells die leaving the brain of the cow to Brain cells die leaving the brain of the cow to look like a sponge.look like a sponge.

It is believed to have come from a similar It is believed to have come from a similar disease in sheep called disease in sheep called scrapiescrapie. .

Viral ReplicationViral Replication