Viruses Ch. 20

Is a Virus Alive? Lets first look at organisms we know are alive? What can you tell by comparing the virus to the cells we have learned about?

What is a Virus? Viruses- segments of nucleic acids contained in a protein coat. Viruses are not cells and not alive. Smaller than prokaryotic cells. Replicate by infecting host cells and using the host DNA to make more viruses. Viruses do not grow, do not have homeostasis, and do not metabolize.

Why are viruses important? Pathogens- agents that cause disease. Viruses are often restricted to certain kinds of cells. – Ex. HIV infects immune cells of animals. – Ex. Bacteriophages- viruses that infect bacteria.

Discovery Late 1800’s in tobacco plant and identified in 1935 TMV (tobacco mosaic virus)- stunts the growth of tobacco plant.

Structure Capsid- virus protein coat. – contain either RNA or DNA, but not both. Envelope- membrane surrounding capsid. – Helps virus enter cell. Glycoproteins- projections on envelope made of proteins & carbohydrate molecule, derived from host cell. Helps virus attach to host. Glycoproteins

Bacteriophage Structure

Viral Shapes Spherical Helical Rod Shaped Polyhedral

Viral Categories RNADNA HIV – Human Immunodeficiency VirusWarts – Human papillomavirus FLU – Influenza VirusChicken Pox – Varicella Zoster Virus Rabies – Rabies VirusMononucleosis – Epstein-Barr Virus Hepatitis C – HepatitisGenital Herpes - Herpes simplex 2, can be 1 Viruses divided into 2 categories based on whether they contain RNA or DNA. Rabies FluHerpes Virus Mononucleiosis

Replication – 2 Types 1.Lytic cycle- viral infection, then replication, and then cell destruction. – Once cell is destroyed, the viruses are then released. 2.Lysogenic cycle- virus stays inside cell but do not make new viruses. – Viral gene is inserted into the host chromosome which is called a provirus. When the cell divides the provirus divides. – Virus replicated without destroying cell. – example: Herpes virus

Assignment Draw a diagram of a Bacteriaphage and an spherical Virus. Label, color, and give some examples of each. Pg. 437 and pg. 192