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Viruses, Viroids, and Prions

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Are Viruses Living or Are Viruses Living or Non-living?Non-living?

Viruses are both and neitherThey have some properties

of life but not othersFor example, viruses can be

killed, even crystallized like table saltHowever, they can’t

maintain a constant internal state (homeostasis).

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What are What are Viruses?Viruses?

A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.

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Viral Viral HistoryHistory

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Discovery of VirusesDiscovery of VirusesBeijerinck (1897)

coined the Latin name “virus” meaning poison

He studied filtered plant juices & found they caused healthy plants to become sick

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Tobacco Mosaic VirusTobacco Mosaic Virus

Wendell Stanley (1935) crystallized sap from sick tobacco plants

He discovered viruses were made of nucleic acid and protein

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SmallpoxSmallpoxEdward Jenner

(1796) developed a smallpox vaccine using milder cowpox viruses

Deadly viruses are said to be virulent

Smallpox has been eradicated in the world today

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Size of VirusesSize of Viruses

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Viral Viral StructureStructure

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CharacteristicsCharacteristics

Non living structuresNoncellularContain a protein coat called

the capsidHave a nucleic acid core

containing DNA or RNACapable of reproducing only

when inside a HOST cell

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CharacteristicsCharacteristics

Some viruses are enclosed in an protective envelopeSome viruses may

have spikes to help attach to the host cellMost viruses infect

only SPECIFIC host cells

CAPSID

ENVELOPE

DNA

SPIKES

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CharacteristicsCharacteristics

Outside of host cells, viruses are inactive

Lack ribosomes and enzymes needed for metabolism

Use the raw materials and enzymes of the host cell to be able to reproduce

EBOLA VIRUS

HIV VIRUS

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CharacteristicsCharacteristics

Some viruses cause disease

Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola

Some viruses may cause some cancers like leukemia

Virus-free cells are rare

MEASLES

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Helical VirusesHelical Viruses

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Polyhedral VirusesPolyhedral Viruses

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Complex VirusesComplex Viruses

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Herpes VirusHerpes Virus

SIMPLEX I and II

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AdenovirusAdenovirus

COMMON COLD

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Influenza VirusInfluenza Virus

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Chickenpox VirusChickenpox Virus

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Papillomavirus – Papillomavirus – Warts!Warts!

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RNA or DNA VirusDo or do NOT have an

envelopeCapsid shapeHOST they infect

Used for Virus Used for Virus IdentificationIdentification

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Bacteriophages

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PhagesPhages

Viruses that attack bacteria are called bacteriophage or just phage

T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

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T-phagesT-phages

The most commonly studied T-phages are T4 and T7

They infect E. coli , an intestinal bacteria

Six small spikes at the base of a contractile tail are used to attach to the host cell

Inject viral DNA into cell

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T-Even Bacteriophages

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RetrovirusesRetroviruses

HIV, the AIDS virus, is a retrovirus

Feline Leukemia Virus is also a retrovirus

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Viroids & PrionsViroids & Prions

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ViroidsViroidsSmall, circular

RNA molecules without a protein coat

Infect plantsPotato famine

in IrelandResemble

introns cut out of eukaryotic

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Prion Prion DiseasesDiseases

Prions form Prions form insoluble deposits in insoluble deposits in the brainthe brain

Causes neurons to Causes neurons to rapidly degeneration.rapidly degeneration.

Mad cow diseaseMad cow disease (bovine spongiform (bovine spongiform encephalitis: BSE) is encephalitis: BSE) is an examplean example

People in New People in New Guinea used to suffer Guinea used to suffer from from kurukuru, which they , which they got from eating the got from eating the brains of their enemiesbrains of their enemies

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Viral Viral ReplicationReplication

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The Lysogenic CycleThe Lysogenic Cycle

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Latency in Latency in EukaryotesEukaryotesSome eukaryotic

viruses remain dormant for many years in the nervous system tissues

Chickenpox (caused by the virus Varicella zoster) is a childhood infection

It can reappear later in life as shingles, a painful itching rash limited to small areas of the body

SHINGLES

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Latency in EukaryotesLatency in EukaryotesHerpes viruses also

become latent in the nervous system

A herpes infection lasts for a person’s lifetime

Genital herpes (Herpes Simplex 2)

Cold sores or fever blisters (Herpes Simplex1)

SKIN TO SKIN CONTACT

PASSED AT BIRTH TO BABY

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VirulenceVirulence

VIRUS DESTROYING HOST CELL

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Treatment for Treatment for Viral DiseaseViral Disease

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VaccinesVaccines

An attenuated virus is a weakened, less vigorous virus“Attenuate" refers to procedures that

weaken an agent of disease (heating)A vaccine against a viral disease can

be made from an attenuated, less virulent strain of the virusAttenuated virus is capable of

stimulating an immune response and creating immunity, but not causing illness

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