Viruses, like 98% of all parasites, are very Host specific. What are parasites? What are hosts? What are pathogens? Viruses can ONLY survive & reproduce in very specific cells of very specific organisms! Different viruses can infect Plants, or Animals, or even specific microbes.

Viruses come in many different shapes, often they have geometric shapes.

Bacteriophage or Phage Can infect only a particular species of bacteria

Why do Virologists like to work with Bacteriophages? What do you think the binding site would be???

Viruses are subcellular No cell parts / organelles More like a piece of a chromosome = A group of genes (DNA or RNA) wrapped in a protein coat (capsid) Are viruses alive??? On borderline between life and non-living.

Viruses are so small they could NOT be seen until the Electron Microscope was invented (1930’s) Compare the size of a Virus to Prokaryotic cell to Eukaryotic cell

Viruses are obligate parasites They do NOT do most Life Functions They have only one goal – to reproduce

Like a Lock and Key, each virus can infect ONLY cells with the very specific binding site, or certain protein in the cell membrane, that the virus protein can attach to or “unlock” the passage into the cell! For example, HIV can only infect the T- 4, (or CD-4) Lymphocyte. Unfortunately for humans, the T-4 lymphocyte is the “Field Commander” of our Immune System, which is why HIV is so devastating to humans. Could HIV infect a cat? Feline Leukemia is “AIDS” in cats!

Lysogenic Viruses