Story time with Mr. Forbes

The tale of virus replication

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.