Friday, 1 February 2013

SCRIPT in progress.


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What is a Virus? A Virus is an infectious agent that replicates only within the cells of living hosts: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope.

(Life Cycle, Animation)

When a virus comes in contact with a target cell it enters what is known as the attachment phase.  Using it’s forged protein signature it makes use of the cells active transport system called endocytosis which inducts the virus into the cell inside of a vesicle.  Once inside the cell the DNA or RNA inside the virus is transcribed into the cell’s nucleus and then translated by the golgi apparatus.  This new RNA is then brought to the ribosomes where proteins are constructed and new viruses are built.  

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(First slide)
(World Map indicating virus spread)

What happens through HIV infection?
The infection leads to low levels of CD4 T cells - which are the host of aid HIV replication  through three main mechanisms. The first mechanism directs viral killing of infected cells. Next it increases rates of apoptosis (cell death) in the infected cells. Followed by the killing of infected CD4 T cells by CD8 cytotoxic lymphocytes. A cytotoxic T cell is a type of white blood cell that kills cancer cells and cells that are infected especially with viruses, or cells that are damaged in other ways. As the CD4 T cell numbers decline below a critical level; the cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.

Measles Virus

Measles virus targets immune cells that express glycoprotein, which serve as an entry receptor for measles.  Measles virus infects epithelial cells, and endothelial cells and neurons. The first infected cells transports virus to nodes where T and B cells become infected. Measles virus is highly cytolytic. In peripheral tissues, adjacent infected calls may fuse together forming giant cells, or syncytia. This process occurs through the action of the viral fusion protein, which is expressed on the surface of infected cells. The skin rash is immune-mediated due to infection of dermal capillary endothelial cells and immune complex formation. Infection of lung epithelial cells that occurs late during the infection cycle mediates transmission to other hosts.

Influenza Virus

When the influenza virus infects a host cell, its goal is to produce many copies of itself that go on to attack even more cells. A viral polymerase both copies the genetic material of the virus and steers the host cell machinery towards the synthesis of viral proteins. It steals a cap from host cell RNA molecules then adds it onto its own. The cap is a short extra piece of RNA that much is present at the beginning of all messenger RNAs  to direct the cell’s protein-synthesis machinery to the starting point. The viral polymerase binds to host cell RNA via its cap, cuts the cap off and adds it to the beginning of its own RNA. This process is known as ‘cap snatching’.

H1N1 Virus (Swine Flu)

-       The swine flu virus uses its antigens to attach to the surface of cells in the nose, throat and lungs.The cell engulfs the virus. The virus is able to pierce the bubble of cell membrane that encloses it and release its RNA cargo into the cell. In the nucleus, copies of the viral RNA are made. Viral messenger RNA (mRNA) causes the cell to make viral proteins. These proteins and RNA migrate to the cell’s surface where they are assembled into new virus particles.  New virus start budding off from the cell surface.
Life cycle of swine flu, H1N1 can be initiated very easily because it is known to live outside of humans for 2 to 8 hours. It can attach itself to any surface touched by an infected person. 

Rabies Virus

Rabies begins the replication process at the site of inoculation, usually as the result of a bite.  By having its translation occur inside the cytoplasm the virus can propagate very quickly.  Rabies will first attack the central nervous system and then later spread to other tissues in the body. The highest concentration of of rabies propagation takes place in the soft tissues of the mouth, creating the tell tale foaming saliva of a rabies victim.  Most rabies victims will die 2-10 days after the first symptoms appear.  The main cause of death is usually dehydration or asphyxiation as selective paralysis takes place in the throat and diaphragm.

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