Virus

Virus: Nucleic acid encased in a protein shell called the capsid.
These organisms are not alive in the usual sense. When not in a medium they are essentially huge macromolecules and in fact some have been crystallized.

Lytic cycle: The cycle of viral infection, replication, growth of new viruses, and (usually) rupture of the cell. (Lysis means "rupture".)

• Attachment to host cell.
• Absorbtion by host cell and release of viral nucleic acid or injection of viral nucleic acid into host. (At this point the viral DNA is sometimes inserted into the host DNA as a provirus.)
  For retro viruses at this stage there is the extra step of making DNA templates from the viral RNA using reverse transcriptase.
• Replication machinery of host is used to copy viral DNA.
• Viral DNA is used to direct host protein synthesis machinery to make the viral proteins.
• Assemby of new viruses followed by the release of new viruses from the host cell (lysis) generally destroying the host cell.

Provirus: A portion of viral DNA that has been incorporated into the host cell's DNA. There it waits until activated when new viral bodies are formed.

Retrovirus: A type of virus that contains RNA and uses the enzyme reverse transcriptase to catalyze the production of DNA from the host cells. This DNA will then go on to direct the host cell's machinery to make new viral components.

Types of Viral diseases:

• AIDS, Polio, Rabies,...
• chicken pox, measles, most colds, flus,...

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