1. Viruses

2. Nonliving particle – do not contain all characteristics of life Reproduce by infecting cells Made of 2 things Nucleic acid Capsid – protein coat Smaller than bacteria need electron microscope to view Cause disease

3. Discovery of viruses Tobacco mosaic disease – prompted experiments to find what is causing disease, stunts growth of tobacco plants 1935 – infectious agent was found to be a virus, purified to a crystal (property of chemical) TMV – made of RNA and protein

4. Tobacco Mosaic Virus

5. Structure of a virus Contains capsid Nucleic acid, RNA or DNA, not both May also have Envelope – surrounds capsid Glycoproteins – carbohydrate molecules derived from host cell, recognition Most are helix or polyhedral in shape

7. AIDS Virus

8. Life cycles – host specific Lytic Viral infection, replication and cell destruction Lysogenic Latent period, stays inside cell for a period of time without replicating Becomes part of viral chromosome, provirus When cell divides, viral genome replicates without damaging the cell

10. Misc. Emerging viruses – viruses that evolve in isolated geographic areas and are pathogenic to humans ex. Ebola Infectious particles Prions – particles that are composed of proteins and have no nucleic acid ex. Mad cow disease Viroids – single strand of RNA, no capsid, seen mostly in plants