Viruses

1. Viruses

2. Viruses • 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