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CONTENTS

1. Introduction

2. Virus Structure

3. Virus Replication

4. Virology

5. Virus and Medicine

6. Review

Introduction – Structure – Replication – Virology – Medicine - Review

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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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A Brief History of Virology

Introduction – Structure – Replication – Virology – Medicine - Review

~1400BCFirst written record of virus infections in heiroglyphics found in Memphis, Eygpt

100BC – ChinaProtection from smallpox using variolation practice

1796 - Vaccination

Edward Jenner vaccinated a boy with cowpox-infected material

1880 – Germ TheoryRobert Koch & Louis Pasteur

Pasteur identified rabies to be cause by an agent he termed “virus” from the Latin for ‘poison’.

1892 beginning of

virologyDmitri Iwanowski showed that ceramic filtered extracts from diseased plants could transmit disease to other plants.

1898Martinus Beijerinick work on TMV

Freidrich Loeffler & Paul Frosch work on foot-and-mouth disease in cattle

1909Landsteiner & Popper

Poliomyelitis (Yellow Fever) was the first human disease to be recognized as a viral disease

1950-2003Discoveries of Ebola, West Nile, HIV, SARS

1915-1917Bacteriophages (eaters of bacteria)Frederick Twort & Felix d’Herelle discovered viruses which infect bacteria.

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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 Crytallography – X-rays are directed at a sample. How those rays scatter can be used to determine the structure of that 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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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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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.

Introduction – Structure – Replication – Virology – Medicine - Review

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The End

Introduction – Structure – Replication – Virology – Medicine - Review

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VIRUSA living thing that provides a source of energy for a virus or an organism

Organisms that live on or near a host and cause it harm.

A tiny, nonliving that invades and then multiplies inside of a cell.

A virus that immediately goes into action. It begins to take over cell functions and produce the virus’s proteins and genetic material.These parts then assemble into new viruses. The viruses multiply like a copy machine left on. When it is full it bursts open – releases the new viruses and dies.

Some viruses hide for a while and become part of the cell’s genetic material. It may stay inactive and “hidden” for years. Then under certain conditions it becomes active and acts like an active virus. Ex – cold sores

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How Viruses Multiply•Active viruses enter cells and immediately begin to multiply, leading to the quick death of the invaded cells.

- Viruses

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How Viruses Multiply

•Hidden viruses “hide” for a while inside host cells before becoming active.

- Viruses

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Active and Hidden Viruses Activity

•Click the Active Art button to open a browser window and access Active Art

about active and hidden viruses.

- Viruses

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Deadly Virus

•Click the Video button to watch a movieabout deadly viruses.

- Viruses

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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