1. Non-living 2. Not cellular 3. Unable to reproduce except in a host cell 4. Smaller than bacterial cells 5. CANNOT BE TREATED WITH ANTIBIOTICS; only vaccines

STRUCTURE: 1. Nucleic acid core – DNA or RNA 2. Capsid – protein over coat 3. Outer envelope – additional outer coat

SHAPE Helical Rod-shaped spherical Round icosahedron 20-sided figure w/ 12 corners Complicated combinations Different shapes for head and tail

Influenza Virus

1. Virus that infects bacterial cells 2. Structure – combination of icosahedrons and helical

1. Polio – affects nervous system 2. HPV – human papillomavirus causes warts 3. Measles – affects skin cells 4. AIDS – caused by HIV; affects immune system 5. Common cold – spread through contact and droplet inhalation 6. Influenza – spread through contact and droplet inhalation

Viral Replication  Lytic and Lysogenic cycles are two different methods of viral replication.  While they are different, they can be interchangeable or the replication can involve both methods in separate phases.

Lysogenic Virus  The viral DNA or RNA enters the cell and becomes part of the cell's genetic material.  This may alter the cell's characteristics, but it does not destroy it.  Does not produce progeny.  There are no symptoms of viral infection.  Some viruses first replicate by the lysogenic cycle and then switch to the lytic cycle.

Lytic Virus  Viral DNA destroys Cell DNA and takes over cell functions.  Destroys the cell.  Produces progeny.  There are symptoms of viral infection.  The cell wall bursts – this process is called lysing - and the new viruses are released.

Prion  A disease-causing agent that is neither bacterial nor fungal nor viral.  Contains no genetic material.  A protein that occurs normally in a harmless form.  By folding into an irregular shape, the normal prion turns harmful. It then converts other normal prions to become harmful.  Example: Mad Cow Disease