the amazing world of viruses
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The Amazing World of Viruses
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Viral Viral HistoryHistory
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Discovery of Discovery of VirusesViruses
•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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Tobacco Mosaic Tobacco Mosaic VirusVirus
•Wendell Stanley (1935) crystallized sap from sick tobacco plants•He discovered viruses were made of nucleic acid and protein
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SmallpoxSmallpox•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
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Viewing VirusesViewing Viruses•Viruses are smaller Viruses are smaller than the smallest cellthan the smallest cell•Measured in Measured in nanometersnanometers•Viruses couldn’t be Viruses couldn’t be seen until the seen until the electron microscope electron microscope was invented in the was invented in the 2020thth century century
Interdependence
Viruses and organisms relyon their environmentand other species for survival.
VirusesBut, Viruses are NOT cells.
A virus is an infectious agent made up of:
•a core of nucleic acid (RNA or DNA)
•a protein coat
Alive or not?Even scientists disagree as to whether or not viruses are alive. What do you think? Look at the chart on the next page to help you decide.
CELLCELL VIRUSVIRUS
Made of cells YES NO
Obtain & use energy
YES NO
Grow & develop
YESOnly inside a living cell
Reproduce YESOnly inside a living cell
Respond & adapt
YES YES
Contain RNA or DNA
YES YES
Characteristic
of life
Alive or not?Most scientists do not
consider viruses to be living because don’t have the
necessary parts to reproduce on their own.
They MUST infect a cell and use its parts to reproduce.
Structureof a virus
Because viruses don’t carry around the necessary parts to reproduce themselves they are very simple structures.
ENVELOPE
NUCLEIC
ACIDCAPSID
Structureof a virus
Consists of 2 parts:
1. A Nucleic acid -either DNA or RNA
2. Capsid – A protein Coat that surrounds and protects the DNA/RNA
ENVELOPE
NUCLEIC
ACIDCAPSID
Types of Viruses1. Standard DNA based Virus2. Retro Virus3. Bacteriophage
Basic VirusA strand of nucleic acid
surrounded by a protein coat.
DNA RNA Protein
RetrovirusA virus that
contains RNA instead of DNA
Human Immunodeficiency Virus (HIV) is a retrovirus
HIV causes AIDS
ENVELOPE
RNA
CAPSID
BacteriophageA virus that
infects only bacteria.
CAPSID
DNA
TAIL FIBER
HEAD
CAPSID
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Helical VirusesHelical Viruses
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Polyhedral Polyhedral VirusesViruses
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Complex Complex VirusesViruses
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Ticking time bombs . . .
Viruses CANNOT reproduce, EXCEPT inside a living cell. They
invade a living cell and let the cell work for them.
Virus CycleA Viral Infection has 2 possible stages:
1.Lytic Cycle
2.Lysogenic Cycle
*Some viruses go straight to the lytic phase and never enter the lysogenic phase
Virus Cycle
1. Lytic Cycle - stage where virus is actively reproducing and killing host cells
2. Lysogenic Cycle - stage where virus is inactive and host cells remain unharmed
Lytic Cycle1. The virus injects its DNA into the
host cell
2. The DNA uses the host cell’s resources and organelles to make new viruses.
3. The viruses cause the cell to burst
4. The cell dies and the newly made copies of the virus are released to go infect new cells.
5. The cycle continues.
1 2 3
4 5
Cycle Illustration
Lysogenic Cycle1. The Virus injects its DNA into the host
cell.
2. The DNA inserts itself into the host cell’s DNA and stays there inactive.
3. There are NO symptoms of the infection at this stage.
4. Eventually the viral DNA will remove itself from the host cell’s DNA and the lytic cycle will begin.
LyticCycl
e
Lyso-Genic
Cycle
Role of virusesAll viruses are parasites: they benefit while
harming the host cell/organism.
Viruses cause disease in every kind of organism—animals, plants, fungi, protists, and bacteria.
Are hard to cure, but many can be prevented by
•Good hygiene•Immunization
Viral diseases
• HIV• Measles• Smallpox• Influenza• Chicken pox
• Common cold• Herpes• Warts• Mononucleosi
s• Mumps
Some viral diseases
MEASLES
Mumps
SMALLPOX
HERPES
1918 Flu
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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 Chickenpox VirusVirus
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Papillomavirus – Papillomavirus – Warts!Warts!
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Helical VirusesHelical Viruses
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Polyhedral Polyhedral VirusesViruses
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Complex Complex VirusesViruses
Linkshttp://www.virology.net/Big_Virology/BVFamilyIndex.html
http://www.virology.net/Big_Virology/BVFamilyIndex.html
Biology, Kenneth R. Miller & Joseph Levine, 1991, Prentice-Hall, Inc., Englewood Cliffs NJ.
Biology: The Web of Life, Eric Strauss & Marylin Lisowski, 1998, Scott Foresman Addison Wesley, Menlo Park CA
TAKS Power Tools, Glencoe Science, Glencoe McGraw-Hill, 2001, New York, NY.
Microsoft Office Clipart
Sources
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