Download Viruses - Lytic and Lysogenic

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
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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.