Evidence 3 (continued): Science Blog


The blog went on to explain how scientists performed an experiment to test Interferon:

Applying the Central Dogma:

How DNA is related to Proteins


The central dogma of molecular biology explains that DNA codes for RNA, which codes for proteins. We need to undertsand how this process works. 

We'll take a look at how a cell can prtect itself from a virus - and in this process determine just how the Central Dogma works. 


This module is a hands-on module - you will really need to read over and understand each piece of evidence and build a model that describes your idea of the Central Dogma.  You will be applying what we've been learning - this is the proof that you not only know the process, but can explain it thoroughly.

Let's start by learning about Viruses:


  • What is a virus?






















  • How do Viruses Infect cells?


  • Does Everyone Exposed to HIV get AIDS?


Models to consider:

Evidence to consider:

Evidence 3: Science Blog


In looking for information about viruses, I came across a blog written by a High School student. 

This is what I found:

Viruses cannot reproduce on their own.

Viruses need to get inside a cell to make more viruses.


How a Virus reproduces:

  1. The virus needs to bind to an  anchor on the cell’s surface, like a key fits a lock

  2. The virus then injects genetic instructions (nucelic Acids) into the cell

  3. The cell uses the virus  genetic instructions to make more viruses

  4. The cell bursts open, and all of the newly made viruses are released into the body


So now let's learn a little about HIV:

What is HIV and AIDS?


The first thing we need to know is that HIV and Aids are NOT THE SAME THING

  • HIV is the name of the virus (Human Imunodeficiency Virus) that infects people

  • AIDS is the name of the disease (Aquired Immune Deficiency Syndrome) caused by the virus.

  • AIDS refers to damage to the immune system

  • The numbers of white blood cells that fight infection get lower over time because HIV kills these cells

  • AIDS gets worse the longer a person has HIV


An HIV positive person, who also has AIDS, has a damaged immune system. Because their immune system is damaged, they get sick more easily. Thier immune system is unable to fight off disseases because the "fighter cells" (white blood cells) are destroyed by the HIV virus.  So, HIV does not kill the person directly - it kills off the white blood cells.  Withiout white blood cells to fight off infections, other infections like the flu or bacteria, kill the person.  AIDS weakens a persons immune system, making it impossible to fight off infection.






  • How is the HIV Virus Transmitted from Person to Person?

Chance of Transmission

Blood transfusions from HIV positive individual                            90%

Mother to infant during birth                                                           25%

Mother to infant during birth with preventative medicine            2%

Contaminated needles to inject drugs                                                1%

Unprotected sex                                                                                  0.5%

In the early 1990s journalists and scientists heard rumors that a few people were possibly resistant to HIV.  These people were exposed to the virus many times but never developed AIDS or got sick. 


How was this possible?  We'll look at what we know about viruses, get some new evidence, and try to figure it out.

FIV stands for Feline Immunodeficiency Virus.  FIV is a virus that attacks the immune system in  cats in a way similar to how HIV attacks the immune system in humans.


FIV was first observed in house (domestic) cats .  Dr. Stephen O’ Brien noticed that house cats could get FIV very easily, and he was worried that this devistating virus would spread from house cats to large wild cats like cheetahs, lions, and pumas.  Many of these species of wild cats are endangered and could become extinct if attacked by thi9s virus. 


Dr. O’Brien gathered blood samples from thousands of wild cats from around the world.  He analyzed these samples, using well known, reliable techniques for analyzing for the presence of the FIV virus.


O'Brein was surprised to find that most wild cats like cheetahs, lions, and pumas already had FIV in their blood.  He was especially surprised to find that these infected cats were not negatively affected by the virus.  These cats possessed a genetic mutation that makes them resistant to the disease. 


Even though the wild cats get the virus, they do not become sick. Unfortunatly, house cats do not have this genetic mutation, and are not resistant to the disease. When house cats get infected with FIV, they become very sick and can die.


Dr. O’Brien concluded that wild cats are genetically resistant to FIV, and house cats are not genetically resistant to FIV.  His studies were very thorough, based on all the blood samples of thousands of wild cats and house cats.





















Use the Evidence Matrix, Relationship Arrows, and Writing Rubric to evaluate the models that follow and determine which best describes the mechanism for immunity. 

  • Evidence 1: A Similar Virus found in Felines:

  • Evidence 2: The Burke Family:

Evidence 4: Jennifer's Blog: A Genetic Professor studying HIV immunity


Upon further investigation on the Internet, I was able to come across the on-line diary of a geneticist studying HIV immunity.  Jennifer (the owner of the diary) documented the findings in the hospital where she was working with a team on HIV immunity.  All of her information was published in reputable scientific journals, and she summarized the information for the layman.

Research Diary: 

General Hospital Genetics Department

Dr. Jennifer Medico, Head Researcher

   Test #1




This is what I found:

Each of the test tubes had HIV virus added to them. 

  • Tube 1 contained white blood cell membranes known to contain all four proteins.

  • Tube 2 contains whit eblood cell membranes from people infected with HIV

  • Tube 3 contained white blood cell membranes from people exposed to HIV, but never became infected





Proteins found in each tube

CD3, CCR5, CCR7, CD8

CD3, CCR5, CCR7, CD8


These results will be published in a

Scientific Journal later this month. 

CD3, CCR7, CD8

Evidence 5: CCR5 Research


Scientists wanted to find out whether HIV can get into cells that do not have the CCR5 protein on their membrane.  So, experiments were conducted to test this idea.


Trial 1:

  1. Blood samples were taken from 40 induviduals who have the CCR5 protein on their white blood cells.

  2. HIV was added tro each of these blood samples.

  3. Cells were examined under High Powered Microscopes.


Trial 2:

  1. Blood samples were taken from 40 individuals who did NOT have the CCR5 protein on their whote blood cells.

  2. HIV was added to each of these blood samples.

  3. Cells were examined under High Powered Microscopes.


  • Each sample was tested to see if HIV was outside the white blood cell (this was expected, because this is where the HIV virus was placed)

  • Each sampe was also tested to see if HIV had passed through the white blood cell membrane and was now inside the cell. (This would mean the cell was now infected with HIV).


Results are shown below:

White blood cells that have the CCR5 Protein.

The cell that have the CCR5 protein were covered with HIV viruses on their surface.
The red dots are HIV viruses on the surface of the cell.

White blood cells that do NOT have the CCR5 Protein.

The cell without the CCR5 protein did not have any HIV viruses on  their surface.

Evidence 5: DNA Analysis


DNA from 15 people who have the CCR5 protein (people resistance to HIV infection) were compared with DNA from 15 people who do NOT have the CCR5 protein (people with HIV infection).








  • Model A: HIV is Attacked and Destroyed

  • Model B: HIV Can't get into the Cell

  • Model A: HIV is Attacked and Destroyed

  • Model B: HIV Can't get into the Cell

Models to consider:

Which model better explains the evidence you have been given?

There is a difference between these two strands of DNA