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Gel Analysis – Teacher Notes
Ursinus College
Essential Background for Students- Students should have a knowledge of genetics and
viral life cycles before doing this lab. They should also have done a gel electrophoresis
lab.
Step 1
Introduction- You should give a brief talk before the lab to stress the importance of
research in HIV/AIDS and give some important background information. Some of the
following facts may be helpful.
It is estimated that over a million people in the United States are presently living
with HIV/AIDS and that 40,000 new cases are diagnosed each year. World wide, it is
estimated that there are 40 million cases and 25 million people have died from the disease
since 1981.
The virus destroys the helper T cells which are specialized white blood cells that
recognize invading organisms. Without these T cells, our bodies are unable to react to
invading disease organisms so while the HIV virus does not kill people directly, it shuts
down the immune response and allows infected people open to a wide range of diseases.
HIV is a retrovirus which means it uses RNA as its genetic material instead of
DNA. Once the viral RNA enters a host cell, an enzyme allows the RNA to be coded
into DNA and that DNA can join with the host cell DNA. Scientists have never been
able to make a vaccine for a retrovirus. Although there is no cure, there are effective
medicines that enable people with HIV to live longer and healthier lives.
In studying HIV and AIDS, researchers found that while most people are
susceptible to the disease, amazingly, a few people in the world appear to be immune to
the disease. One of them is Steve Crohn, who is a topic of discussion in the introductory
video. They also found some people in whom the disease progressed, but very slowly.
The goal of this lab is to try to explain these unusual cases of resistance.
Step 2
Show Video Labeled “CCR-5 Beginning”
At the end of the video, tell students that we are now going to look for a genetic
link to why people vary in their resistance to HIV.
Step 3
Introduce the Gel Analysis Program
Hand out the Gel Analysis instructions. Have student pull up the CCR-5 research
program on the student disks and give a brief overview of what they are looking at and
how the program works. The purpose of this analysis program is to quantify the results
of gel electrophoresis. Have them go to page 2 on the program and read the introduction
before going on and point out that the data for the lanes and the information for the
standard ladder are also on page 2.
Step 4
Students Analyze the Gel, Print Results, & Write Report
The time you want to spend on this activity will determine the detail that you will
request on the report. You could just have them write a paragraph and probably finish in
a period or you could assign the report to be finished overnight and turned in the next
day.
Step 5
Show Video Labeled “End”
This video will allow students to see if they were correct in their conclusions and
get a glimpse into the potential of this discovery.
LAB RESULTS
The reason for the immunity to HIV in this case is a mutation in the CCR-5 allele.
People with no immunity have 2 copies of the normal CCR-5 allele, hence the one band
on the gel since both alleles are the same. The immune person in this case has two
mutant alleles that have a 32 base pair deletion. The mutant alleles cannot code for the
CCR-5 protein that the HIV virus needs for attachment to the cell and therefore the virus
cannot enter the cell. People who have some immunity are heterozygous and have one
normal and one mutant gene. If students are careful they should be able to exactly
recognize the 32 base pair deletion. This mutant allele is called delta 32.
If you are looking for a follow up activity, you could have students see if they can
find out where this mutant gene came from because the history aspect of this gene is quite
interesting. Researchers have found that it is only found in people of European descent.
Asians and people of African descent do not have the delta 32 allele. Researchers
recently determined that the mutation showed up during the bubonic plague also called
the Black Death that wiped out more than half the population of Europe. While the Black
Death was caused by bacteria, it used the same system to enter cells as the HIV virus.
The mutation provided resistance to the plague and the evolutionary pressure of the
plague sweeping Europe selected for this allele.
Science in Motion – Ursinus College – by Ron Faust