1. Viruses (18.2) SB3D. Compare & contrast viruses with living organisms.
State Standard
SB3D. Compare & contrast viruses with living organisms.

2. Why aren’t they considered to be living?
Viruses—An Exception
A virus is a nucleic acid (core) surrounded by a protein coat (capsid).
Why aren’t they considered to be living?
Viruses are not cells, nor are they made of cells.
Viruses cannot reproduce without a host cell.
Viruses lack the machinery needed to carry out the functions of life.
Because viruses are nonliving, they usually are not placed in the biological classification system.

3. More virus traits…
the core can be made of DNA or RNA (but never both!)
very small.
NOT living.
Can reproduce by hijacking living cells.
The capsid helps the virus bind to the host cell.

4. T4 Bacteriophage
- A virus that attacks E. coli bacterial cells

5. E. Coli and the Bacteriophage
What it looks like in real life

6. The HIV Virus

7. The Chicken Pox Virus

8. The Influenza Virus

9. The Small Pox Virus

10. The Ebola Virus

11. The Polio Virus

12. There are two types of viral infection cycles:
Lytic (Active)
Lysogenic (Dormant)

13. Lytic (active) Infection
Virus enters the host cell.
Virus makes copies of itself.
The new copies cause the cell to burst.

14. The
Lytic
Cycle

15. Lysogenic (dormant) Infection
A virus embeds its DNA into the DNA of the host cell.
The virus’s DNA is replicated (copied) along with the host cell’s DNA.
The cell does NOT burst/lyse immediately.
Certain conditions can cause the dormant virus to switch to an active lytic cycle.

16.                                                                 
The
Lysogenic
Cycle

17. Cycle of Lytic and Lysogenic

18. Viruses often cause observable symptoms
Antibiotics are useless against viruses, because viruses are not alive
Ex. AIDS, Smallpox, Polio, Measles, the Common Cold

19. Vaccines
Since viruses can’t be cured, our only defense against them is prevention.
We accomplish this through the use of vaccines.
Vaccines contain a weakened or dead form of the virus that is injected into the body.

20. Retrovirus Changes DNA into RNA. Mutates quickly
And example of a Retrovirus is HIV