viruses! pre-quiz (true or false) 1. many common illnesses are caused by viruses. 2. viruses are...

Viruses!

Pre-Quiz (True or False)1. Many common illnesses are caused by viruses.2. Viruses are easily killed by drugs such as antibiotics.3. Once you have contracted a specific virus, you will not get sick from this

virus again because of the antibodies produced in your body.4. Many diseases caused by viruses can be avoided through vaccination.5. Viruses are very fragile and cannot live on surfaces outside fo the human

body.6. Viruses have the ability to change themselves, or mutate, over time.7. Viral illnesses cannot be transferred from animals to people.8. The only way to transmit viruses is through close physical contact with an

infected person.9. Viruses can become resistant to drugs used to treat them.10. One of the best ways to prevent the spread of viral diseases is frequent,

thorough hand washing.

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

Most Biologists consider viruses to be non-living because:Are not cellsDo not use energy to grow or respond to their

surroundingsCannot make food, take in food, or produce wastesViruses do not respond to stimuli in the environment such

as light, temperature, chemicals, sound, gravity, heat, water and pressure.

They can only multiply like other organisms but only inside a living cell

What are Viruses?What are Viruses?Definition-Definition-

Viruses are noncellular particles made up of genetic material and protein that can invade living cells.

Small, non-living, invades and reproduces inside a living cell

1 virus- can produce thousands of new viruses

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Discovery of VirusesDiscovery of Viruses

Beijerinck (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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Wendell Stanley (1935) crystallized sap from sick tobacco plants

He discovered viruses were made of nucleic acid and protein

Discovery of VirusesDiscovery of Viruses

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Edward 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!!

Discovery of VirusesDiscovery of Viruses

How Big is a Virus?Viruses are very small – smaller than the smallest cell.

They may vary in size from 20-400 nm. Measured in nanometers (nm = one billionth of a meter)one millionth of an inch1000x smaller than bacteriaBacteria = much smaller than a human cell

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CharacteristicsNon living structures Non-cellularContain a protein coat called the capsidHave a nucleic acid core containing DNA or

RNA (one or the other - not both)Capable of reproducing only when inside a

HOST cell

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Characteristics

Some viruses are enclosed in an protective envelope

Some viruses may have spikes to help attach to the host cell

Most viruses infect only SPECIFIC host cells

CAPSID

ENVELOPE

DNA

SPIKES

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CharacteristicsCharacteristicsOutside 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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CharacteristicsCharacteristicsViruses cause many common illnesses diseases

Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola, the “flu,” chicken pox, measles, polio, and hepatitis

Some viruses may cause some cancers like leukemia

MEASLES

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Viral Attack

Viruses are very specific as to which species they attackHOST specificA vector is a host that transfers viruses to another

organism

Example – West Nile Virus is spread through mosquitoes

Humans rarely share viral diseases with other animals

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5 Steps of Lytic Cycle

1. 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 viruses 5. Release of the new viruses into the

environment (cell lyses)

INFECTION

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Viral LatencyViral Latency

Some viruses have the ability to become dormant inside the cellCalled latent virusesThey may remain inactive for long periods of time (years)Later, they activate to produce new viruses in response to some external signal

HIV and Herpes viruses are examples

What do Viruses look like?Viruses are unusual and different from other things in nature.Viruses come in a variety of shapes

Some are rod-shaped, round-shaped, tadpole-shaped, many-sided, helical, cube-like and so on.

Some may be helical shape like the Ebola virusSome may be polyhedral shapes like the influenza virusOthers have more complex shapes like bacteriophages

THEY JUST DON’T LOOK LIKE OTHER THINGS!

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Types of Viruses: Helical Viruses

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Polyhedral Viruses

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Complex Viruses

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SIMPLEX I and II

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Adenovirus

COMMON COLD

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Influenza VirusInfluenza Virus

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Chickenpox VirusChickenpox Virus

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Papillomavirus – Warts!Papillomavirus – Warts!

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PhagesPhages

Viruses that attack bacteria are called bacteriophage or just phage

They have a head, neck and tail

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Characteristics of Characteristics of RetrovirusesRetroviruses

Contain RNA, not DNAFamily RetroviridaeContain enzyme called Reverse TranscriptaseWhen a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cellExamples: HIV

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Small, circular RNA molecules without a protein coat

Infects plants

Potato famine in Ireland

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Prion DiseasesPrion DiseasesPrions have no DNA or Prions have no DNA or RNARNA

Prions form insoluble Prions form insoluble deposits in the braindeposits in the brain

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

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

Chronic Wasting Disease Chronic Wasting Disease (CWD)(CWD)

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Latency in EukaryotesSome eukaryotic viruses remain dormant for many years in the nervous system tissues

Chickenpox (caused by the virus Varicella zoster) is a childhood infectionIt can reappear later in life as shingles, a painful itching rash limited to small areas of the body

Herpes viruses also become latent in the nervous system

A herpes infection lasts for a person’s lifetimeGenital herpes (Herpes Simplex 2)Cold sores or fever blisters (Herpes Simplex1)

SHINGLES

HOST SPECIFICITYAll kingdoms can be infected by virusesViruses that infect organisms of one kingdom are not able

to infect organisms of another kingdomViruses can infect species of organisms that are closely

related or not closely related (some viral diseases can be passed from different species)

Viruses can even be species specific (only passed within the same species)

Spread is specific to the type of virus -Carrier organisms, the air, direct transfer of body fluids

-Surfaces on which body fluids have dried

PARASITISMViruses are parasites.

A parasite is an organism that depends upon another living organism for its existence in such a way that it harms that organism.

Viruses must infect living cells in order to carry out their functions of growth and reproduction.

Viruses depend upon their hosts for respiration, nutrition and all the other functions that occur in living things.

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Vaccines 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 virus

Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

Viral IllnessTreatment of viral disease include vaccination, vector

control, and drug therapyDrug therapy does NOT work very wellVaccination and vector control are the most successful way

to beat virusesVaccination works because once you are exposed to and

overcome a virus your immune system creates antibodies that will immediately attack the virus if it shows up again

Hand-washing is effective against bacterial diseases and viral diseases

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Other Viral Treatments

Interferon are naturally occurring proteins made by cells to fight virusesGenetic altering of viruses (attenuated viruses)Antiviral drugs (AZT)Protease inhibitors – prevent capsid formation

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Reducing the RiskCover mouth/nose when you sneeze of coughWash hands frequentlyAvoid contact with the body fluids

***Not foolproof but reduces the risks***

Pre-Quiz (True or False)1. Many common illnesses are caused by viruses.2. Viruses are easily killed by drugs such as antibiotics.3. Once you have contracted a specific virus, you will not get sick from this

virus again because of the antibodies produced in your body.4. Many diseases caused by viruses can be avoided through vaccination.5. Viruses are very fragile and cannot live on surfaces outside fo the human

body.6. Viruses have the ability to change themselves, or mutate, over time.7. Viral illnesses cannot be transferred from animals to people.8. The only way to transmit viruses is through close physical contact with an

infected person.9. Viruses can become resistant to drugs used to treat them.10. One of the best ways to prevent the spread of viral diseases is frequent,

thorough hand washing.