February 14, 2013 | 2
Invited Guest Post by Helene Brazier-Mitouart
I have a Ph.D. in Cell Biology and Health and I am currently doing research in cancer biology as a postdoctoral associate at Weill Cornell Medical College in New York City. Besides having a passion for making scientific discoveries, I also have a great interest in teaching science to children. For this reason, I am part of an afterschool program lead by the New York Academy of Sciences (NYAS) in partnership with the Department of Youth and Community Development. The program aims to bring the sciences to afterschool classrooms of 4th to 8th graders of New York City and Newark. For the last year I have been teaching a group of 5th graders at a public school in Chinatown. Recently, Stephanie Wortel, the Education Program Coordinator for the NYAS gave me the opportunity to try a DNA extraction kit created by the company Bio-Rad with my class and then to write about it for Scientific American. That was an offer I couldn’t resist!
For me, the beauty of biology lies in the extraordinary mechanisms that control the development of an organism, in all the proteins that orchestrate complicated signaling pathways, and how so much of that complexity relies on tiny little DNA. I know that science can be hard to understand and conceptualize at times, especially when dealing with the microscopic. So imagine introducing genetic concepts to 10-year-old children. It is a challenge! In that spirit, Bio-Rad has developed a new kit, known as “Genes in a Bottle” to allow children (and curious adults!) to extract their own DNA (Deoxyribonucleic acid, to be precise) from the cells in their mouths. The kit is available free of charge to scientists who volunteer in schools.
My students already knew a lot about DNA. They were able to explain to me that DNA was a twisted double helix and that the nucleotides A-T-C-G were coding the genetic information that makes us who we are. When I introduced the idea that they would get to see their own DNA using the Biorad kit, they were very enthusiastic and eager to start the experiment.
The first step in isolating our DNA was to gently scratch the inside of our cheeks with our teeth in order to release some cells from which we would be isolating our DNA. We gathered these cells by rinsing our mouths with water and then collecting this water in an experimental plastic tube. Next, we gently mixed the water containing our cells with a first solution called a “lysis buffer”. The lysis buffer contained a detergent that disrupted the lipid membrane of the cells. This step was allowing the contents of the cell, including the DNA and many types of proteins, to be released from the inside of the cell. My students immediately noticed the visible changes that were occurring in the reaction tube.
“Oh! There is some weird stuff in the tube!! What is it?” exclaimed one student.
“The contents of the cells have been released in your tube. This is mostly DNA mixed with proteins.” I replied.
“But we just want the DNA, right?” asked another student.
“Exactly! That’s why we will now need to destroy the proteins in order to isolate pure DNA.”
For this reason, the kids next added a few drops of protease to their tubes. The protease is a molecule (for science geeks, it’s an enzyme!) that is able to break down proteins into little pieces.
In order for the proteins to be degraded by the protease, the experimental tubes had to be incubated at 50°C (122°F). The students felt like they were chemists, checking the temperature on the thermometers over and over again! The reaction needed around 10 minutes to happen, and it was not easy for some of the students, who were full of energy and eager to get their DNA, to patiently wait for the reaction to occur. At the end of the 10 minutes, the kids were holding their precious tubes, which contained a mix of broken lipids (destroyed by the detergent), broken proteins (destroyed by the protease), and DNA.
The final step in the isolation process was to make the DNA come out of the mixture. To do so, each student had to very slowly add cold alcohol to her tube. This caused the DNA to precipitate out of the solution, as DNA is less soluble in cold alcohol than in water. In addition, because we had added some salt to the solution, the DNA molecules aggregated together, generating a sort of tangled yarn-ball of DNA.
“Wow!” cried one student. “Is this white thing in my tube really my DNA?” I smiled and said: ”Yes it is!”
“And me? What about my tube? I have a lot of milky stuff! Are you sure it’s my DNA?”
“Yes it is” I assured them.
The DNA that the students were looking at with so much passion was the DNA from a few thousand cells in their mouths. This DNA contained millions of genes that together formed the recipe book that makes everyone who they are.
The students were very excited and compared their quantities of DNA with enthusiasm. Unfortunately, some of the students were also a little disappointed because they couldn’t see any DNA in their tubes. Of course it wasn’t because they didn’t have DNA in their cells, but that one of the reactions that was supposed to have occurred during the protocol didn’t take place. Being a scientist is not always easy and can be frustating, I explained, but it is worth the effort!
For the lucky ones, the Biorad kit contained little heart-shaped glass containers on a necklace to store the DNA. The students went home that day with the secret of their genetics proudly hanging around their necks. Even though some of my students were not successful at isolating their DNA with the Biorad kit, the excitement of the group as a whole made up for it. All of the kids learned a lot during this scientific activity, not only how to follow specific instructions and be active in understanding the experiment, but also to explore their own biology in a new way!
More to Explore:
* Here’s a link to Bio-Rad’s “Science Ambassador” program, which is offering the DNA kits free of charge to scientists who volunteer in classrooms.
* If you’re a scientist looking for volunteer opportunities or a teacher looking for a scientist to come to your class, visit our “1,000 Scientists in 1,000 Days” project and sign up.