Viruses continued
Life 2
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
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
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!
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 .
http://www.youtube.com/watch?v=VvTfkMhEw3g
Viral Replication
Viruses continued
Viral Replication Replication cycles
Viral Replication Viruses can’t reproduce themselves, they must use the cells of a another organism Require another cell to survive = Obligate intracellular parasite
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
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
Viral Replication We will watch a short clip depicting virus replication: You will identify the THREE key components to viral replication
Lytic Infection Where a virus: Enters a cell Immediately copies itself Causes the cell to burst (Lyse) Ex. T4 Bacteriophage
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
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
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
Prophage 5. 6.
A prophage is
Bee venom to prevent virus infection http://www.youtube.com/watch?v=VNPQecZ8SBIhttp:// www.youtube.com/watch?v=VNPQecZ8SBI