viruses

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VIRUS

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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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We have all gotten viruses…

from bacteria, plants to animals.Viruses cause colds, flu, warts and

diseases such as measles, AIDS and cancer.

AND not all viruses are harmful to humans.

BUT not all viruses cause diseases,

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WHAT IS A VIRUS?

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A VIRUS is either DNA or RNA, that is protected by a protein coat called a CAPSID.

DNA CAPSID

VIRUS

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Virus Structure

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• Non living structures• No cellular• 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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• 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

DNA

SPIKES

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•Outside 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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Why are some viruses harmful?

Virus invades cell

Virus forces cell to make copies of virus

Eventually so many copies are made, the cell explodes,releasing all of the new viruses

When your cells make viruses instead of operating normally, YOU get sick

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DISEASE VIRUSES

AIDS HIV

WartHerpes Simplex Virus

Flu Influenza

Measles Morbillivirus .

Cancer Hepatitis B

Examples of some viral diseases:

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How the viruses infect ?

• Viruses infect Bacteria– These viruses are called Bacteriophages

• Viruses infect Plants– One example is the Tobacco Mosaic

Virus

• Viruses infect Animals– One example is the common cold

Viruses usually infect a specific host including:

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What is the size of the virus?

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•Viruses are Viruses are smaller than the smaller than the smallest cell.smallest cell.

•Measured in Measured in nanometers.nanometers.

•Viruses couldn’t be seen until Viruses couldn’t be seen until the the electron microscope electron microscope was was invented in the invented in the 2020thth century. century.

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Viruses range in size from 20 nanometers (nm) – 250 nanometers (nm)

10-5 m10-6 m

10-7 m

10-8 m

10-9 m

10-10 m

0 m

virusesanimalcellsbacteriap

rote

ins

ato

m

Go five more feet!

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Viral ShapesViral Shapes•Viruses come in a variety of shapes•Some may be helical shape like the Ebola virus•Some may be polyhedral shapes like the influenza virus•Others have more complex shapes like bacteriophages

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Helical CapsidsHelical capsids are rod-like structures with the RNA in the center of the helix. A Helix is made by stacking repeating units in a spiral.

RNA

protein coat

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Tobacco Mosaic VirusTobacco Mosaic Virus (TMV) is an example of a virus with a helical structure. Protein subunits wrap around the spiraling RNA strand.

This image taken using an Electron Microscope

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INFLUENZA VIRUS …. SURROUNDED BY AN ENVELOPE WITH SPIKES

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Flu virus

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AdenovirusAdenoviruses cause diseases like pink-eye or the common cold

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Adenovirus, a exposed virus, with a polyhedral capsid and a fiber at each corner

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Complex VirusesComplex Viruses

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BacteriophageBacteriophage is infect bacteria

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Herpes VirusHerpes Virus

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Enveloped Viruses

Enveloped viruses are viruses which have a membrane coat surrounding the protein coat or capsid. These viruses are common in animal viruses, but are uncommon in plant viruses.

Herpes Simplex Virus.

A membrane (made of proteins) surrounds the capsid (also made of proteins) which surrounds the viral DNA.

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How do viruses replicate?

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Replication Phases

V - Release- Assembly of virus

DNA and protein coat into whole new viruses

- Leaving the cell

Phase I

Phase II

Phase IV Phase V

Phase III

I, II, III - Viruses enter cell- Attachment to cell

membrane- Penetration inside cell- Losing virus protein coat

IV - Replication- Tricks cell into

making more viral DNA

- Tricks cell into making viral protein coat

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Are Viruses Living?A table where one column represent properties of living organisms and the second column represent properties of a virus.

Properties of Living Organisms

Properties of Viruses

Breathes (respires) Doesn’t breathe

Metabolizes Doesn’t metabolize

Grows Doesn’t grow

Reproduces Reproduces

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Atomic Force Microscope – A tiny tip probes a surface, from which the shape of the surface can be determined

X-ray Crystallography – X-rays are directed at a sample.

Techniques to Study Viruses

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Filters – Very small holes in material filter only viruses through

Sedimentary Centrifugation – A sample is spun so fast, different elements in it are separated by density

Electron Microscope – Electrons are smaller than light wavelengths, so viruses can be “seen” by reflecting electrons off of them

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