Objectives: Describe the structure of viruses. Explain how viruses cause disease. Explain how humans defend against viral disease.

 They are not living (they are not made up of cells).  They are parasitic (they require a host cell to make copies of itself).  They have a very simple structure.

 A virus that attaches itself to much larger bacteria such as E. coli.  After injecting its DNA into the bacterium, the DNA forces the bacterium to produce new viruses.

Lytic Cycle:  The phage attaches to the host cell and injects it’s DNA into it (b,c).  The phage use the host cell’s organelles to replicate (d,e).  Host cell bursts open releasing many copies of the virus (f).  The new viruses look for their own host cells (a).

Lysogenic Cycle  Virus injects it’s DNA into host cell (a,b,c).  Each time host cell reproduces, it copies the viral DNA as a part of the host DNA (d,e).  The copied DNA leaves host cell and starts a lytic cycle (f).

 Influenza (flu)  H1N1  Common cold  West Nile

 Since viruses are not living they cannot be killed with antibiotics.  We must wait until our immune system destroys the virus.  Vaccines can help protect against viral diseases, but not all of them such as the common cold and HIV.