Viruses A submicroscopic pathogen From the Latin: Poison: A slimy liquid

Viruses  Not usually considered to be a living organism  Symptoms depend on the host cells that they infect to reproduce  Inserts its genetic material and takes over host’s functions to produce more viral protein and genetic material instead of the cell’s usual products.

Viruses  Structure outside a host cell  Has an inner core of nucleic acid (RNA or DNA)  Protein coat surrounding nucleic acid  Various sizes and shapes

Viruses  Viruses attaches to a host cell  Virus injects its DNA into host cell nucleus  Then it can do one of two things 1)Lysogenic Phase  RNA from virus becomes part of the DNA in host cell  No obvious change in host cell  It is in the dormant stage until virus gets triggered and enters the lytic cycle

Viruses 2) Lytic Cycle  Host cell’s DNA is destroyed  Cell’s machinery is used to produce new viruses  The host cell breaks open to release the new viruses, which go and infect new cells

Effects of Viruses  They cause disease in all living organisms  When the virus breaks out of the host cell is usually destroys it  Electron micrograph of a cluster of influenza viruses

Viruses  This picture shows the structure of the Human Immunodeficiency Virus(HIV).

Effect of Viruses  They cause disease in plants  Micrograph of the virus that causes tobacco mosaic disease

Effect of Viruses  They cause disease in bacteria  We call them bacteriophages