1. Viruses – What Do We Want to Know?
Vocabulary
Why are viruses considered to be nonliving?
What is the basic structure of a virus?
How do viruses multiply?

2. Let’s pretend………
It is a dark and quiet night. An enemy spy slips silently across the border. Invisible to the guards, the spy creeps cautiously along the edge of the road, heading toward the command center.

3. Undetected, the spy sneaks by the center’s security system and reaches the door.
Hey – look over there!

4. Breaking into the control room, the spy takes command of the central computer. The enemy is in control.
Yea! I’m in control!

5. Moments later the command center’s defenses finally activate
Moments later the command center’s defenses finally activate. Depending on the enemy’s strength and cunning, the defenses may squash the invasion before much damage is done. Otherwise the enemy will win and take over the territory.

6. What is a Virus?
Virus: a small, nonliving particle that invades and then reproduces inside a living cell.

7. Non-Living???
Biologists consider viruses to be nonliving because viruses are:
not cells,
do not use energy to grow or respond to their surroundings
do not make food, take in food, or produce waste products!
The only way viruses are like organisms in in their ability to multiply (reproduce)!

8. Viruses are small and not alive – what do they do?
Viruses multiply – they make MORE of themselves.
They can only do this after they have entered another cell.
Does the ‘spy’ reference make sense now?

9. Vocabulary:
A host is a living thing that provides a source of energy for a virus.
The organism or virus that live ON or IN a host are called parasites.
Almost all viruses act like parasites because they destroy cells when they multiply inside them
A bacteriophage is a virus than infects bacteria.

10. What types of organisms do viruses attack?
Viruses can infect organisms from each of the Kingdoms. Each virus, however, can enter (or infect) only a few types of cells in a few specific species.
Example: most cold viruses in humans only infect cells in the nose and/or throat.
When you have a cold, are you the host or the parasite?

11. Shapes and sizes of Viruses
Streptococcus
Bacterium
(750 nm)
Smallpox Virus (250 nm)
Cold Sore Virus (130 nm)
Influenza Virus (90 nm)
Cold Virus (75 nm)
Yellow Fever Virus (22 nm)

12. How small are viruses?
Here is how you can imagine the size of viruses:
“If a virus was the size of a basketball…”
A single bactera would be as large as a football field
A grain of sand would be two miles long
A person would be 4,000 miles tall

13. Some common viruses. Rabies Virus Human Papilloma Virus (HPV)
Ebola Virus
German Measles Virus
Bacteriophage

14. Structure of Viruses
All viruses have two basic parts: an outer coat that protects the virus and an inner core made of genetic material.
The genetic material contains the information to make a new virus!

15. Outer Coat:
The outer coat is made of proteins. Each virus contains unique proteins in its coat. The shape of the proteins allows the virus’s coat to attach to, or lock onto, certain cells in the host. Like ‘keys’, these proteins only fit into certain ‘locks’.
Why does a virus only invade a specific kind of cell?

16. How Viruses Multiply After a virus attaches to a cell, it enters it!
Once inside, a virus’s genetic material takes over the cell’s functions. The genetic material directs the cell to produce the virus’s proteins and genetic material. These proteins and genetic material are then assembled into new viruses.

17. Active Viruses
After entering the cell, an active virus immediately goes into action. Like a copy machine, the cell will make more viruses until it is FULL. At this point, the cell bursts open releasing all of the new viruses. These can then infect new cells……

18. Active Virus (animation)
Example:
Common Cold
Virus

19. Hidden Viruses
Sometimes the genetic material from a virus does not start ‘working’ right away. Sometimes the genetic material incorporates itself into the normal cell genetic material. At some point, this genetic material ‘turns on’ and starts creating more viruses…

20. Hidden virus Example: Cold Sore or Herpes Virus First virus
Something ‘triggers’ the virus to multiply
Time goes by

21. How do ‘new’ viruses appear
Short video from HHMI

22. Review: Explain why biologists consider viruses to be nonliving?
Describe the basic structure of a virus.
Compare the two ways that viruses can multiply.
Bonus: Scientists believe that viruses could not have existed on earth before organisms (like bacteria) appeared. Use what you know about viruses to support this hypothesis.