viruses, viroids, and prions -...
TRANSCRIPT
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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
3
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/
50copyright cmassengale