Viruses, Viroids, and Prions

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Slide 1

Viruses, Viroids, and Prions

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Are Viruses Living or Non-living?

Viruses are both and neither

They have some properties of life but not others

For example, viruses can be killed, even crystallized like table salt

However, they can’t maintain a constant internal state (homeostasis).

Slide 3

What are 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 History

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Discovery 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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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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Smallpox

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 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

Contain a protein coat called the capsid

Have a 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 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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