Virus

Viral Medicines

1. Acyclovir (For the herpes virus - Cold Sores) 2. AZT, and HIV protease inhibitors (for HIV)

Viral Replication

1. Attachment - The virus attaches to the cell membrane of the host cell 2. Penetration- The host cell allows the virus to enter 3. Uncoating - the virus releases its genetic material within the cytoplasm of the cell 4. Take Over and Replication- The viral DNA/RNA takes over and the host cell is then forced to make copies of the virus. 5. Assemble- New viruses are assembled inside of the host cell 6. Release- New viruses leave by budding out of the cell or lysing the cell.

Types of Viruses

1. DNA Viruses 2. RNA Viruses 3. Retroviruses

Virus Structure

1. Enveloped 2. Unenveloped

Virus Survival Techniques - why they come back

1. Mutation - change their appearance so the immune system doesn't recognize it 2. Lots of different Variations - cold and flu 3, Hiding from the Immune System - resting - come out when the body is stressed 4. Dormant - lay dormant within a cell and wait until the immune system is weak before it comes back

Virus Reproduction

1. The Lytic Cycle 2. The Lysogenic Cycle (Dormancy) 3. Retrovirus (HIV)

What organisms can become Infected by a Virus?

Every living thing has some sort of susceptibility to a particular virus specific for the organism. Plants animalls bacteria - every living thing whether multicellular or single - cell.

Fighting a Virus

Immune System recognizes the virus, alerts the cell disables a virus. *B Cells* ● create antibodies that attch to the virus ● These antibodies prevent the virus from replicating and tag it for destruction. *T Cells* ● Kill infected cells, calls for reinforcements ● Helps B Cells make antibodies Time Lag - It takes time for the body to create the B Cells specific for each new virus. During this "lag" your body gets sick. When the antibodies arrive - it takes some time to destroy all the viral particles.

Viral Release Mechanisms

New viruses leave and infected cell by *budding* out of the cell or *lysing* the cell. ● *Budding* viruses that bud out of the cell take some of the cell's plasma membrane and wrap it around their capsid creating an envelope. ● *Lysing* viruses cause the cell to rupture or lyse, and burst forth from the exploded cell.

Capsid

Outer protein shell of an infectious viral particle called a viron.

Virus Envelope

Part of the previously infected host cells plasma membrane that helps cloak the virus and fool other cells into allowing the virus entry.

Virus

Tiny particle made up of genetic material (DNA or RNA) that can invade and replicate within a living host

Lytic Cycle

Viral Reproduction 1. The virus injects its genetic material into the host cell. The genetic material enters the nucleus and is inserted into that cell's DNA. 2. The cell's nucleus is now programmed differently. The cell immediately begins to use it's machinery to produce the parts of future viroids. Eventually, the parts are assembled and the *cell explodes* (lysis) releasing more harmful viroids.

Lysogenic Cycle

Viral Reproduction In this cycle, the viral genes do not go into action immediately. The viral genetic material simply makes a circle and sits quietly. However, each time that cell divides, it's daughter will have the *dormant* viral material in it.

Retrovirus

Viral Reproduction ● These viruses contain *RNA* as their genetic material. ● After their RNA is inserted into the nucleus, they begin to make DNA from it. The new viral DNA is then inserted into the cell's DNA. ● The cell then follows the directions found in the DNA's code and orchestrates its own demise. ● HIV is a present day retrovirus.

Immunity

You become immune to specific viruses because the body retains the B and T cells created to fight the specific infection. If the virus enters the body again - it will be destroyed before the body gets sick.

What is a Virus

● A virus does have genetic information (genes made of DNA or RNA), which allows it to make copies of itself. ● The virus must be inside a living cell before the information can be used. ● A virus hijacks another life form's DNA and uses the cellular machinery within that cell to make copies of itself. ● The virus controlled DNA directs the infected cell to build all the viral parts necessary to make thousands of new, mature, infectious viruses which can leave the cell to infect other cells.

What a Virus is NOT

● A virus is not a bacterium or a cell, nor is it an independently living organism. ● A virus cannot survive in the absence of a living cell. ● A virus is not alive nor is it dead. ● Viruses do not take in or release energy. ● They do not "grow" or move on their own. ● Antibiotics do not harm a virus; it is for this reason that treatment for the flu for example, is mainly to help ease the symptoms of the illness.

Viron

● An infections viral particle - often just DNA or RNA with a protein shell wrapped around the genetic material. ● Outer proteien shell is the Capsid ● Architectural arrangment of capsid proteins are used to classify viruses ● Some viruses have an additional covering on the outside called an Envelope ● Envelope is part of the previously infected hosts cell's plasma membrane and helps to cloak the virus and fool the next cell into allowing the virus in.

Vaccine

● Forces the body to come in contact with a disabled virus ● The body will create the B and T cells necessary to fight off that specific virus and retains the B&T cells for future use

Why isn't a virus considered Living?

● It does not take in or release energy ● It does not grow or move on its own, and ● Antibiotics do not harm a virus.

Plant and Bacterial Defence Against Viruses

● Plants are protected from certain viruses by substances, which coat leaves and stems and "closing-off" systems, which generate a walled-off area within the plant at the source of the infection. ● Bacteria can be protected from bacterial-specific viruses through the action of enzymes inside the bacterium's cell. However, if a bacterial virus (called a bacteriophage) infects one cell, usually within a very short time, all of the bacterial cells will be killed. If there are no other bacterial cells of that particular species around for that particular virus, however, the virus will "die," too.

Are Viruses Alive?

● They do not respire, eat, excrete, or reproduce. ● By itself, a virus can not do anything. ● Viruses affect every living cell known, from man to bacteria.

Function of Virus

● To make more viruses ● To replicate it must infect and take over a living cell ● Most viruses are only able to infect one species ● Kills the Cell it leaves behind

Size of Virus

● Very Small ● Cannot be seen using a Light Microscope - must use an electron microscope