1. Viruses

2. Viruses Virus comes from the Latin word virus meaning poison
What is a virus?
A particle made of nucleic acid, protein, and sometimes lipids.
Viruses are not members of the Six-Kingdom System of Classification
Infect all taxonomic levels!
They are highly specific

3. Viruses can reproduce only by infecting living cells.
Enter cells and use the cell’s “machinery” to produce more viruses.
Smaller than prokaryotic cells(can only be seen with an electron microscope)
DNA or RNA core surrounded by a protein coat (capsid)
Vary in size and shape

4. Groups of Viruses DNA Viruses Viroids Prions RNA Viruses
Direct production of RNA
Examples
Herpes
Pox
RNA Viruses
retrovirus
Influenza
Rhabdovirus (rabies)
HIV
Viroids
Disease causing agent, RNA with NO capsid
Examples
Plant disease
Prions
Abnormal protein clumps, kills host
Mad Cow Disease

5. Viral Infection Lytic Infection
Virus enters cell, makes copies of itself, and causes cell to burst
Lysogenic Infection
Virus integrates its DNA into DNA of host cell, remains dormant and replicates when cell divides
Viral DNA that attches to cell’s DNA is called prophage or provirus
Enters lytic cycle when DNA removes itself from host DNA

7. Retroviruses RNA viruses Produce DNA from their RNA
The DNA attaches to the host cell DNA and can be dormant for long periods
HIV is an example

8. Are viruses alive? Viruses have many characteristics of living things
Not cellular
Only active in living cells
Occupy a “gray” area between the living and non-living world