Virus - Replication  Bacteria and viruses can both make us sick, but did you know that viruses can make bacteria sick too?.  Let me tell you two little stories about viruses. The main characters are a bacterium and a virus

Story 1 – The LYTIC CYCLE  Once upon a time, there lived a happy little bacterium (maybe floating in your stomach or some spoiled food)

 All of a sudden he began to feel ill.  Maybe he ate something bad.

His health continued to deteriorate. Moments later, his skin rips open and he sees a virus climbing out of him!!

 His day gets worse as he bursts open and an army of viruses spill out of him from inside!

 There are two ways to look at this story….  1) If you are a bacterium, It is your worst nightmare come true.  2) If you are a virus, you’re thinking “We Rule!!”  And it’s true because lots of work went into this plan

How does a Virus do this to a Bacterium?  A) A Virus slips its DNA into a bacterium

How does a Virus do this to a Bacterium?  B) Virus DNA is made up of special materials that destroy the bacteria DNA

How does a Virus do this to a Bacterium?  C) Now that the Bacteria DNA is gone, the virus DNA takes over the cell and tells it to make more viruses (DNA & capsids)  The DNA in a cell is a blueprint and the virus DNA basically changes the blueprints (ex. A car factory switches to making killer robots)  The workers are still doing their jobs but are now following new instructions)  Replacing bacteria with virus DNA turns the cell into a virus factory until the bacterium gets over-filled and breaks open and dies..

 This first story was called the Lytic Cycle  However, this is not the only way viruses attach and replicate…  The other ‘invasion’ is called the Lysogenic Process this story uses secret agent viruses and espionage…

Story 2 -The Lysogenic Cycle  The secret agent cell injects its DNA into the cell but doesn’t do anything harmful…..right away  DUN DUN DUNNNNN!!

 The viral DNA slips into and joins the cell’s DNA  The viral DNA acts as a terrorist sleeper cell – it lies in wait until the signal to act comes.  Once the viral DNA joins the cell’s DNA, a Provirus has been formed.

Provirus (Lysogenic cycle)

 Now, whenever the cell replicates, the viral DNA is replicated as well.  It is now an extended bacteria family, unknowingly filled with sleeper cells.

 And one day….BOOM, Roasted! The Virus DNA releases itself  There are now many copies of the identical infected cells.  The viral DNA takes control of all the cells to create virus factories.  Factories create viruses until all the cells fill to completion and burst! An entire bacteria colony open, spill out bacteria, and die

*Warning*  Although bacteria were featured in this story, it can happen to ANY cell!

Extra notes..  Some viruses contain RNA instead DNA.  Both are genetic material but are made with different sugars.  The signal to activate (or trigger) a provirus can be a change in the host’s environmental conditions or health.  Diseases that come and go throughout an individual’s life are created by the lysogenic cycle.  Ex – Herpes and AIDS

Herpes  When cells are triggered and the virus attacks, the patient will notice symptoms.  When the provirus is dormant, no attack or symptoms are evident

AIDS  Provirus and new viruses are created  When the proviruses are triggered, AIDS will be diagnosed.  When the new viruses are created, individuals are HIV positive.

Prions  Derived from the words protein and infection  Normal proteins in the body that convert into infectious particles  same chemical composition but new molecular shape. (proteins in a misfolded form)  They are the only known disease-causing agent with no genetic material (DNA or RNA)  Cause many diseases such as brain disease and mad cow disease.  These are often diagnosed late

Homework  1. compare and contrast (use a table or a venn diagram) prokaryotic cells, eukaryotic cells and viruses.  2. Compare and contrast the Lytic and Lysogenic systems. (P. 55)  3. Discuss ways the spread of a virus can be prevented.

For Tuesday  Research a particular virus  A) What is the scientific name for the virus  B) What is the common name for the virus  C) Does it have DNA or RNA  D) Does it replicate using the lytic or lysogenic cycle?  E) Who does it affect and how?  Be prepared to share your findings with the class.