1. Viruses
pp. 104 to 107

2. Viruses vs. Bacteria: What’s the difference?
Bacteria  unicellular organisms
Virus  protein-covered genetic material (DNA) that has NO CELLS, but invades other living cells
True or false? “Viruses are living things.”
FALSE!!!

3. What are Viruses? Not a living organism!
Complicated assembly of molecules:
Proteins (protective)
DNA or RNA
Lipids
Carbohydrates
No cells or organelles
Dormant outside a living cell (can’t do anything, including reproduce)
Once it invades a living cell, it
can reproduce

4. Viral Diversity
Viral specificity: viruses can only invade certain host cells (based on DNA, proteins, shape)
Example of viruses: tobacco mosaic virus (tobacco plant), rabies (mammals), swine flu (pigs & humans), HIV (immune system)
Ex. bacteriophage viruses can only infect bacteria

5. Viral Diversity:
Hosts: Plants Animals Animals Bacteria

6. Viral Reproduction
All viruses enter host cells, but some are not pathogenic (infectious) – they do not kill their host or make them “sick”
There are two processes viruses can use to make more copies of themselves:
Lytic Cycle
Lysogenic Cycle

7. Lytic Cycle
Attachment (entrance)  virus chemically recognizes host cell and attaches to it. Whole virus or only DNA enters cell cytoplasm. It integrates itself into host cell DNA.
Synthesis  virus DNA (or RNA) hijacks host cell and programs it to replicate viral components (nucleic acids, enzymes, capsid proteins, etc)
Assembly  all components of virus (nucleic acids, enzymes, proteins) come together to create new virus particles
Release  new virus particles released from the infected cell to find other cells. Host cell dies (lysis).

8. Lysogenic Cyle
Attachment (entrance)  virus chemically recognizes host cell and attaches to it. Whole virus or only DNA enters cell cytoplasm. It integrates itself into host cell DNA.
Reproduction  Viral DNA is replicated along with host DNA during normal mitosis processes (*Remember: mitosis is how cells reproduce*)
Cytokinesis daughter cells of mitosis have virus DNA integrated with their own
Virus will often be in a dormant state (lysogeny) until it becomes activated by a stimulant (eg. Change in pH, temperature, food supply, etc) –” triggers the lytic cycle.

9. Lytic Vs. Lysogenic Cycle
Lytic cycle:
take as little as mins
produces up to 300 new virus particles, but kills host cell
Lysogenic cycle:
host is not killed
many generations of virus can be produced without harm to the host
Virus is dormant until stimulant triggers activation of virus. It will then switch over to the lytic cycle.

10. Examples of Viruses DNA viruses Chicken pox Mono Small pox RNA viruses
Rabies
Measles
Mumps
The Flu
AIDS
Common cold
Some cancers
Symptoms appear as cells are destroyed (lytic cycle)
Most viruses hard to treat since antibiotics (inhibits growth of microorganisms) cannot kill them.
Vaccines:
Vaccines “train” our bodies to defend against viruses. By injecting a small amount of virus (dead or weakened) into our bodies, our immune system learns how to fight it off by building antibodies against it. It builds up an army of WBC’s & antibodies to kill the living virus immediately before it can reproduce. In the future, exposure to that same virus won’t wreak havoc on our bodies and make us sick because antibodies will already be available to fight it off.
This is also why some people feel a little sick after getting their annual flu shot.