1. Viruses Virus: A noncellular particle composed of genetic material that can invade living cells. –Viruses are considered by most to be non- living since they lack metabolism and are not made of cells. Are extremely small Are usually very specific as to what cells they can invade

2. Structure of a Virus: Contain core of genetic information (either DNA or RNA). Genetic material surrounded by a protein coat called a capsid.

3. Life Cycles of viruses Lytic infection : Infection: Virus identifies an attaches itself to a host cell. The genetic material is then injected into the host cell. –Growth: Genetic material of virus overrides host cell's activities. Cell is now instructed to replicate viral genetic material and protein coats. –Lysis: Cell is lysed "broken open" and new viruses are released to infect other cells. This kills the host cell

4. Life Cycles of viruses Lysogenic infection : Similar to lytic infection however important differences exist –Instead of immediately replicating, viral DNA incorporates itself into the host cell's DNA. –Will remain dormant for significant amounts of time. –Give certain conditions, the virus will enter it's lytic phase similar to a normal lytic infection

5. Retroviruses A new form of virus has been identified known as a retrovirus. –Retroviruses are RNA viruses which can conduct a process known as Reverse Transcription In reverse transcription RNA is used to make DNA (the reverse of the normal RNA transcription process). –HIV is a retrovirus.

6. Virus Shapes