1. Standard SB3d: Compare and contrast viruses with living organisms.
Headings
Vocabulary
Important Info
Standard SB3d: Compare and contrast viruses with living organisms.

2. Viruses are NOT Alive!!
They do not grow or develop: they only replicate
They must replicate inside a host cell
They are VERY small: need electron microscope

3. Naming Viruses Diseases they cause: “herpes virus” Numbers: “T4”
If they only infect bacteria: “bacteriophage” or “phage”

4. Virus Structure
Outer protein coat: “capsid”. May be many-sided; spiral; head w/tail
Inner core of nucleic acid: DNA or RNA (HIV)
Some have an envelope around the capsid

5. Virus Structure T4
HIV

6. Attachment to Host Cell
Viruses attach to a specific receptor site on the host cell: “lock and key”
Each virus can only attach to a few kinds of cells
Ex: T4 only infects the bacteria E. coli, wart virus only infects skin cells

7. Viral Replication: Lytic Cycle
Virus enters host cell: “injects” or is taken inside
Virus takes over host cell’s DNA & tells host cell to make new viruses
Virus parts are assembled by the host
Host cell bursts and new viruses are released to infect other cells

8. Viral Replication: Lytic Cycle
1. Virus injects its nucleic acid
2. Virus DNA tells host cell to make more viruses
3. New viruses are assembled by host cell
4. New viruses are released when host cell bursts (“lysis”)

9. Viral Replication: Lysogenic Cycle
Virus DNA enters host cell DNA: “provirus”
Every time host cell divides; it copies the provirus too
Provirus may leave the host DNA at any time and enter lytic cycle
Ex: herpes, hepatitis B, chicken pox, HIV

10. Viral Replication: Lysogenic Cycle
1. Virus injects its nucleic acid
2. Virus DNA enters host cell as a “provirus”
3. Provirus copied with host cell’s DNA
4. New viruses are released when host cells bursts (“lysis”)

11. Treatment for Viruses
Only treatment for a virus is a preventative vaccine before exposure to virus
Vaccine contains heated viruses that can’t infect…but cause antibodies to be made