1. VIRUSES
Text p

2. Cause many diseases

3. Are parasites that infect living cells
When a virus attacks, it shows signs of being alive
Can reproduce
Has biological molecules: protein coat and nucleic acids (DNA, RNA)
HIV
Influenza virus
ebola virus

4. But viruses are not alive
Not cells, have no organelles
No metabolism, does not use ATP
Do not grow, have no chemical reactions
Much smaller than any cell
1/10 the volume of a small bacteria
0.03 to 0.3 μm (10 to 100 x smaller than bacteria)
Each virus attacks only a specific type of cell eg. Plant, animal, bacteria
A virus that infects bacteria is called a bacteriophage (“phage” = to eat)
Discovered with the invention of the electron microscope

7. Bacteriophage

8. VIRAL REPLICATION

9. VIRAL REPLICATION 2 Types of processes Lytic Cycle: has 4 steps
Attachment:
Virus recognizes host cell
Virus attaches to it
Injects whole virus or just DNA or RNA

10. Synthesis:
Viral DNA or RNA instruct the cell to produce new virus parts
Assembly:
New virus parts are brought together and assembled into new viruses

11. Lytic cycle may be completed in only 25-45 minutes
Release:
New viruses are released from the infected cell & the cell dies
Lytic cycle may be completed in only minutes
Hundreds of new viruses produced!

12. The Lytic Cycle

13. VIRAL REPLICATION Lysogenic Cyle
In this cycle, the virus goes into a dormant stage (“sleeping”)
Virus injects its DNA or RNA into the host cell, but it does not take control of the host cell
Instead, the viral DNA becomes part of the cell’s DNA
It is reproduced as the cell is reproduced  all daughter cells contain the virus
The host cell does not die

14. The Lysogenic Cycle

15. At some point, as a result of some stimulation, the virus can be triggered to re-enter the lytic cycle
Eg. Stress like pregnancy, serious illness, surgery, psychological stress