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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,

Introduction – Structure – Replication – Virology – Medicine - Review

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WHAT IS A VIRUS?

Introduction – Structure – Replication – Virology – Medicine – Review

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Introduction – Structure – Replication – Virology – Medicine - Review

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

DNA CAPSID

VIRUS

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Why are some viruses harmful?

Introduction – Structure – Replication – Virology – Medicine - Review

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

Introduction – Structure – Replication – Virology – Medicine - Review

Examples of some viral diseases:

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Who do 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:

Introduction – Structure – Replication – Virology – Medicine - Review

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Let’s look at the Defining Properties of Viruses

• Viruses are parasites that invade cells• Viruses have either DNA (Deoxyribose

Nucleic Acid) or RNA (Ribonucleic Acid)• Viruses direct the synthesis of new virus

within a host cell.• Newly made viruses infect other cells.

Introduction – Structure – Replication – Virology – Medicine - Review

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Cell BiologyLet's review a little cell biology since viruses cannot multiply without the help of cells. The viruses enter the cell and forces the cell to make more viruses.

The cell has three main zones:

Introduction – Structure – Replication – Virology – Medicine - Review

nucleus

membranecytoplasm

Cytoplasm – this is the “factory” where biochemical reactions occur.

Membrane – this double layer protects the cell and allows the cell to communicate with the outside environment.

Nucleus – this holds the DNA or genetic information about the cell.

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DNA/RNA

DNA, deoxyribonucleic acid, is the double-stranded molecule that encodes genetic information (e.g. your hair color, height, etc.) in the nucleus of cells. The complete set of DNA in a cell is called the genome.

RNA, ribonucleic acid, is typically single stranded so that it can be read to make proteins.

Introduction – Structure – Replication – Virology – Medicine - Review

DNA or RNA code for genes that defines who we are.

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How small is a virus?

Introduction – Structure – Replication – Virology – Medicine - Review

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If a cell was the size of your classroom, then an average virus would be the size of a softball.

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

1 nm = 0.00000004 inches

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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Helical Capsids

Helical 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

Introduction – Structure – Replication – Virology – Medicine - Review

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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.

Introduction – Structure – Replication – Virology – Medicine - Review

This image taken using an Electron Microscope

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Adenovirus

Introduction – Structure – Replication – Virology – Medicine - Review

Adenoviruses cause diseases like pink-eye or the common cold

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Bacteriophage

Introduction – Structure – Replication – Virology – Medicine - Review

Bacteriophage is a virus that infects bacteria.

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Enveloped Viruses

Introduction – Structure – Replication – Virology – Medicine - Review

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?

Introduction – Structure – Replication – Virology – Medicine - Review

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Replication Phases

V - Release- Assembly of virus

DNA and protein coat into whole new viruses

- Leaving the cell

http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/adlyt.html

Phase I

Phase II

Phase IV Phase V

Phase III

Introduction – Structure – Replication – Virology – Medicine - Review

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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The concept of a virus as an organism challenges the way we define life:

* Viruses do not breathe.* Viruses do not metabolize.* Viruses do not grow.* However, they do reproduce.

Introduction – Structure – Replication – Virology – Medicine - Review

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Are Viruses Living?

Introduction – Structure – Replication – Virology – Medicine - Review

Create 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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Viruses Can Help Cells, Too

Introduction – Structure – Replication – Virology – Medicine - Review

- Since viruses can transport DNA and RNA into cells, scientists are exploring Gene Therapy

- In Gene Therapy, viral genetic material is replaced with new DNA

- In time, this could be used to cure genetic diseases. Currently we have no cure for these types of illnesses

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Common Viral Diseases

•Unlike with bacterial diseases, there are currently no medications that can cure viral infections.

- Viruses, Bacteria, and Your Health

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The End! And Review• Viruses are very simple: a shell containing

either DNA or RNA.They infect by hijacking cells’ machinery to

force them to make more viruses.• Viruses are tiny, even compared to a cell.• Some viruses may prove useful in gene

therapy as natural carriers of DNA that was specially designed to be good for a particular reason.

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The End

Introduction – Structure – Replication – Virology – Medicine - Review