1. Viruses

2. What are viruses?
small, non-living, infectious particles containing genetic material in the form of DNA or RNA with a protein capsule, called the capsid.
Non-cellular particle

3. Highly specific about what they invade
Over 4000 virus species classified but scientists believe that there are millions
Highly specific about what they invade
ex: plant viruses infect only plant cells
specialize in the cell types they infect.

4. Features of Viruses: Viruses have no cytoplasm
Less than 0.1µm in diameter (100s of 1000s of viruses could fit inside a human cell)
Cannot grow or reproduce on their own
Do not produce energy; do not create waste
Take control of the cell that they infect

5. Viruses – Living or Non-Living?
Considered non-living because:
Do not metabolize energy
Do not perform cellular respiration
Cannot grow
Cannot reproduce on their own (act as parasites)

6. Shapes of Viruses

7. Viral Diseases
Mild viral diseases such as the common cold or chicken pox, or more severe viral diseases such as AIDS or cholera, are all infectious.
Epidemic: outbreak confined to a geographical region
Pandemic: widespread, global epidemic

9. Bacteriophages

10. Vaccination preventions against viruses.
mixtures that contain weakened forms or parts of dangerous virus.
they trigger a response by the immune system without causing an infection.
creates a form of chemical ‘memory’ allowing immune system to react quickly if the individual ever comes in contact with the real virus.

12. 3 ways Viruses enter living cells:
1) enter bacterial cells by punching a hole in the cell wall and injecting its DNA

13. 2) enter plant cells through tiny rips in the cell wall
3) enter animal cells by endocytosis

14. Infectious Cycles Viruses must invade a living host cell to reproduce
There are two ways to do this
1. Lytic Cycle
2. Lysogenic Cycle

15. 1.Lytic Cycle
the virus enters the cell, replicates itself hundreds of times, and then bursts out of the cell destroying it

16. 2. Lysogenic Cycle
the virus enters the cell, viral DNA integrates with the host DNA and becomes inactive, the host functions normally
an environmental change may then cause the virus to enter the Lytic Cycle

17. Differences Between Lytic and Lysogenic Cycles
In the Lytic Cycle:
Viral DNA destroys Cell DNA, takes over cell functions and destroys the cell.
The virus replicates and reproduces.
There are symptoms of viral infection.
In the Lysogenic Cycle:
Viral DNA merges with cell DNA and does not destroy the cell.
The virus does not reproduce.
There are no symptoms of viral infection.

18. The Origin of the Virus The origin of the modern virus is unclear.
Two hypotheses exist:
They could be runaway stretches of nucleic acid from a larger organism that detached and became active, therefore new viruses are forming frequently and many do not have ancestors
Viruses once lived outside of host cells, but over time due to their parasitic lifestyle, they lost the genes necessary to live outside the host 18

19. Videos
Flu Virus
Ebola
HIV/AIDS

20. Homework:
Why are viruses considered to be non-living?
What characteristics do viruses share with all living things?
Which viral diseases are quite common and associated with the winter season?
Explain the relationship between a virus’s dormant period in a cell and the appearance of cold sores.