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Viruses

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Viruses

Video link

video link - abcnews

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Are Viruses Living or 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 Viruses?A virus is a particle

made up of genetic material and protein that can invade living

cells.parasites – nobenefit

Pathogens disease causing agent

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Viral History

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Discovery of VirusesBeijerinck (1897)

coined the Latin name “virus” meaning

poisonHe studied

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

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Tobacco 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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SmallpoxEdward 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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Viewing Viruses

Viruses are smaller than the smallest cell

Measured in nanometers

Viruses couldn’t be seen until the electron microscope was invented in the 20th

century

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Size of Viruses

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Viral Structure

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Characteristics

Non living structures

Noncellular – no traditional cell parts

Contain a protein coat, capsid, and nucleic acid core containing DNA or

RNA

Capable of reproducing only when inside a HOST cell

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Characteristics

Some viruses are enclosed in an

protective envelopeSome viruses may have spikes to help attach to the host cellMost viruses infect only SPECIFIC host cellsOutside of host cells,

viruses are inactive

CAPSID

ENVELOPE

DNA

SPIKES

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Herpes Virus

SIMPLEX I and II

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Adenovirus

COMMON COLD

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Influenza Virus

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Chickenpox Virus

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Papillomavirus – Warts!

Smallpox

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RNA or DNA Virus

Do or do NOT have an envelope

Capsid shape

HOST they infect

Ways to Identify a Virus

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Retroviruses

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Characteristics of Retroviruses

Contain RNA, not DNA

Contain enzyme called Reverse Transcriptase – synthesizes DNA from viral RNA

When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme

into the cytoplasm of that cell

HIV – human immunodeficiency virus – causes AIDS.

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ENZYME

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Prions

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PrionsPrions are “infectious

proteins”Prions form insoluble

deposits in the brainCauses neurons to

rapidly degeneration.Mad cow disease

(bovine spongiform encephalitis: BSE) is an example

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Viral Replication

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Viral Attack

Viruses are very specific as to which species they attack

Humans rarely share viral diseases with other animals

Virulent or temperate

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virulent viruses

Viruses take over and the destroy the host cell quickly

EX. influenza, ebola, cold

Lytic Cycle

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5 Steps of Lytic Cycle

1. Attachment - Virus attaches to the cell

2. Penetration (injection) of viral DNA or RNA

3. Replication of new viral proteins and nucleic acids

4. Assembly (Maturation) of the new viruses5. Release of the new viruses into the environment (cell lyses)

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Attachment:Phage attaches to host cell.

Penetration:Phage pnetrates host cell and injects its DNA.

Merozoites released into bloodsteam from liver may infect new red blood cells

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2

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Bacterial cell wall

Bacterial chromosome

Capsid DNA

Capsid

Sheath

Tail fiber

Base plate

Pin

Cell wall

Tail

Plasma membrane

Sheath contracted

Tail core

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4 Maturation:Viral components are assembled into virions.

Tail

5 Release:Host cell lyses and new virions are released.

DNA

Capsid

Tail fibers

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One-step Growth Curve

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Lysogenic VirusSome viruses become dormantinside the cell

Called temperate virusesForm a prophage of viral and

cell DNA may remain inactive for years

Later, they activate to produce new viruses in response to some external signal

HIV and Herpes viruses

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Lysogenic CycleOnce a prophage cell is activated, host cell enters

the lytic cycle and the cell lyses

INACTIVE STAGEACTIVESTAGE

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Virulent Viruses

HOST CELL

LYSES & DIES

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The Lysogenic Cycle

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Latency in EukaryotesChickenpox is a childhood

infection but can reappear later in life as shingles

Herpes viruses – latent in nervous system

A herpes infection lasts for a person’s lifetime

Genital herpes (Herpes Simplex 2)

Cold sores or fever blisters (Herpes Simplex1)

SHINGLES

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Virulence

VIRUS DESTROYING HOST CELL

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Lytic and Lysogenic Cycles

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Treatment for Viral Disease

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VaccinesInjection of a weakened, less vigorous virusOnly way to prevent from getting a virusstimulate an immune response, creating immunity, but not causing illnessEX. gardasil, MMR, tetanus, menactra, flu shot

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Other Viral Treatments

Interferon are naturally occurring proteins made by cells to fight viruses

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Viral DiseasesFlu, cold, herpes, hepatitis, AIDS, ebola, chicken pox, conjunctivitis (pink eye), croup, whooping cough, pertussis, epstein-barr, hanta virus, HPV, measles, mumps, rubella, polio, rabies, SARS, smallpox, West Nile

How are they spread?

1. Carrier organisms – mosquitoes, fleas

2. Air

3. Direct contact - transfer of body fluids

Who is equipped to handle diseases?

CDC Atlanta, GA

Tracks all infectious diseases

Centers for

Disease

Control

Who is equipped to handle diseases?

USAMRIID U.S. Army

Fort Detrieck, MDUnited

States

Army

Medical

Research

Institute

Infectious

Disease

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References

Information for this powerpoint was obtained from Cheryl Massengale, biology teacher in Little Rock, AR.

Massengale, C. (2009, April 26). PowerPoints. Retrieved April 26, 2009, from Massengale's Biology Junction: http://www.biologyjunction.com/

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