BACK NEXT

VIRUS

BACK NEXT

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

BACK NEXT

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,

BACK NEXT

WHAT IS A VIRUS?

BACK NEXT

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

DNA CAPSID

VIRUS

BACK NEXT

Virus Structure

BACK NEXT

• 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

BACK NEXT

• 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

BACK NEXT

•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

BACK NEXT

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

BACK NEXT

DISEASE VIRUSES

AIDS HIV

WartHerpes Simplex Virus

Flu Influenza

Measles Morbillivirus .

Cancer Hepatitis B

Examples of some viral diseases:

BACK NEXT

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:

BACK NEXT

What is the size of the virus?

BACK NEXT

•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.

BACK NEXT

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!

BACK NEXT

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

BACK NEXT

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

BACK NEXT

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

BACK NEXT

BACK NEXT

INFLUENZA VIRUS …. SURROUNDED BY AN ENVELOPE WITH SPIKES

BACK NEXT

Flu virus

BACK NEXT

AdenovirusAdenoviruses cause diseases like pink-eye or the common cold

BACK NEXT

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

BACK NEXT

Complex VirusesComplex Viruses

BACK NEXT

BacteriophageBacteriophage is infect bacteria

BACK NEXT

Herpes VirusHerpes Virus

BACK NEXT

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.

BACK NEXT

How do viruses replicate?

BACK NEXT

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

BACK NEXT

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

BACK NEXT

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

BACK NEXT

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

BACK NEXT