1. Viruses

4. Are Viruses Living Things?
Characteristics of Living things are…
Made of cells
Can reproduce
Based on a universal genetic code
Grow and develop
Obtain and use materials and energy
Respond to the environment
Maintain homeostasis
As a group, change over time * *

5. Viral Characteristics
NON-LIVING
REPRODUCE ONLY WITHIN A HOST CELL by hijacking the cells’ machinery
NAMED FOR DISEASE THEY CAUSE OR PLACE
THEY INFECT

6. Which type of cell will be infected by the virus shown below?

7. Name tells you this virus infects bacteria

8. Name tells you this virus causes influenza

9. Viral Size
Viruses are very small. If an average virus were the size of an average person, a bacterial cell would be the size of a dinosaur over ten stories tall.
Click on the picture for virus size activity

10. Whiteboard Activity
Cell, Virus or Both

11. Activity: Cell, Virus, or Both?
Contains nucleic acid as genetic material
Both

12. Activity: Cell, Virus, or Both?
Can grow and develop
Cell

13. Activity: Cell, Virus, or Both?
Can only replicate in a host
Virus

14. Activity: Cell,Virus, or Both?
Can reproduce on its own
Cell

15. Activity: Cell, Virus, or Both?
Obtain and use materials and energy
Cell

16. Activity: Cell, Virus, or Both?
Respond to the environment
Cell

17. Activity: Cell,Virus, or Both?
Maintain homeostasis
Cell

18. Activity: Cell, Virus, or Both?
Can contain DNA
Both

19. Activity: Cell, Virus?
Which is smallest?
Virus

20. Activity: Cell, Virus, or Both?

21. Activity: Cell, Virus, or Both?

22. Ask students to note similarities and differences that they see in these pictures.
Point out that the viruses all contain the same “major parts (i.e. genetic material and capsid), but are specific for specific types of cells. Viruses are typically classified according to the type of organism they infect.

23. Viral Structure All viruses have: genetic material (DNA or RNA)
Capsid: protein coat that enables a virus to enter a living cell

24. How do viruses infect cells?
Once a virus enters a host cell, two different processes can occur:
Lysogenic cycle
Lytic cycle

25. Lytic Cycle Click on Picture for Video
Virus enters the cell, makes a copy of itself, and causes the cell to burst.
Click on Picture for Video

26. Lytic Cycle viral DNA is injected into the host cell
host cell begins to make mRNA from the viral DNA
viral proteins shut down the host cell’s regular functions
cell is used to make thousands of viruses (DNA and protein coats)
host cell bursts (lyses) and releases viruses to infect other cells

27. Lysogenic Cycle
Host cell makes copies of the virus indefinitely. Virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA. Lysogenic viruses remain inactive for a period of time and do not lyse the cell immediately.

28. Lysogenic Cycle viral DNA is injected into the host cell
DNA is integrated into the host DNA
host cell divides with the viral DNA as a part of it
eventually the viral DNA can be triggered to separate from the host cell DNA and pick up with the lytic cycle at step 2.

29. Turn to the person next to you and discuss the difference between the lytic and lysogenic cycles.

31. How do RNA viruses work?
RNA viruses do not have built in proofreading, so they mutate and evolve quickly (like the flu).
A special kind of RNA virus, called a retrovirus, can cause DNA to be made from their RNA.
Certain cancers, and AIDS are caused by retroviruses.