1. Viruses
continued

2. Life 2

3. Last class we pondered…. What is alive?
Figuring out what makes something alive is not easy
Life is incredibly varied, so our definition has to include everything from sea sponges to ourselves

4. What is alive? Figuring out what makes something alive is not easy
Life is incredibly varied, so our definition has to include everything from ……. bacteria or virus ……to humans

5. What Unites Living Things?
All living things are united by the following characteristics:
They are made of cells
They reproduce
They are based on a universal genetic code
They grow and develop
They respond to their surroundings
They maintain Homeostasis (from Greek: "hómoios", "similar", and stásis, "standing still")
As groups, they change over time (Evolve)
Most argue viruses are not alive!

6. Are Viruses Living Things?
They are made of cells
They reproduce
They are based on a universal genetic code
They grow and develop
They respond to their surroundings
They maintain Homeostasis
As groups, they change over time (Evolve)
One could argue that viruses are not living things because they do not grow nor develop independently .

8. Viral Replication

9. Viruses
continued

10. Viral Replication
Replication cycles

11. Viral Replication
Viruses can’t reproduce themselves, they must use the cells of a another organism
Require another
cell to survive =
Obligate intracellular parasite

12. Review: Virus structure: outer protein coat termed caspid
(the most simple)
Virus structure: outer protein coat termed
caspid
and DNA or RNA housed inside
The terms virus and bacteriophage categorize viruses by
what type of cell they infect
eukaryotic cells
(varicella zoster virus –chicken pox- infects humans)
prokaryotic cells (bacteria)
(T4 bacteriophage)
Viruses infect
Bacteriophage infect

13. Viral Replication
Remember, viruses can’t reproduce themselves, they must use the cells of a another organism
They do this in one of two methods:
Lytic infection
Lysogenic infection

14. Viral Replication
We will watch a short clip depicting virus replication:
You will identify the THREE key components to viral replication

15. Lytic Infection Where a virus: Enters a cell Immediately copies itself
Causes the cell to burst (Lyse)
Ex. T4 Bacteriophage

16. Lytic Infection- details
Entry: The virus attaches to a specific host cell and injects its DNA into the host
The host cell make copies of the virus
The host can’t tell it from it’s own DNA and begins to make mRNA (messenger RNA) from viral DNA
This viral mRNA is used at the host’s ribosomes to make viral proteins
These viral proteins assemble to be new viral particles
The cell then bursts releasing the new viruses

17. Viral Replication
Remember, viruses can’t reproduce themselves, they must use the cells of a another organism
They do this in one of two methods:
Lytic infection
Lysogenic infection – the same steps as the lytic cycle but with a twist

18. Lysogenic Infection- steps
Entry: The virus attaches to a specific host cell and injects its DNA into the host
The viral DNA is incorporated into the host’s DNA the embedded viral DNA is termed provirus/prophage
The host cell replicates
Host replicates and makes more cells containing the provirus/prophage
Eventually the provirus/prophage removes istelf from the host DNA and directs the synthesis of new virus particles by
tell it from it’s own DNA and begins to make mRNA (messenger RNA) from viral DNA
This viral mRNA is used at the host’s ribosomes to make viral proteins
These viral proteins assemble to be new viral particles
The cell then bursts releasing the new viruses

20. Prophage 5. 6.

22. A prophage is

23. Bee venom to prevent virus infection