AP Bio Class Tests DNA

By Victor Lee ’16 and Kimberly Ho ’16

Swishing a saline solution in their mouths, AP Biology students extracted their mitochondrial DNA, and by using Polymerase Chain Reaction, they were able to copy and sequence their DNA at the Dolan DNA Center located at Harlem on March 3.

Deoxyribonucleic Acid (DNA) is a molecule composed of sugars, phosphates, and nucleic acids (adenine, thymine, guanine, cytosine). The sequence of the nucleic acid differentiates people apart as everyone’s DNA is slightly different.

“Students learned more details about mitochondrial DNA and why it is useful for studying ancestry,” said Miss Melissa Lee, the lab instructor. “They also learned how to extract and amplify DNA, and confirm their results through gel electrophoresis.”

Prior to the lab activity, the class studied properties of DNA, DNA replication, DNA transcription, and DNA translation,  Also, students learned various techniques in order to extract, copy, and sequence DNA.

“It’s very difficult to understand certain molecular biology techniques unless you perform them in a hands-on way,” Miss Lee added. “For example, gel electrophoresis is difficult to understand when only learning from a paper or online simulation. There’s nothing like doing the real thing.”

Before the lab, Miss Lee lectured the students on the basis of the lab such as DNA, DNA replication, and evolutionary patterns based on DNA sequences. Additionally, usage of tools such as pipettes were demonstrated.

“We studied this topic near the start of the year. Before the trip, we were all a little fuzzy on this topic,” said Helen Wong ‘15.

In order to extract the DNA, students first had to extract cells from their mouths, as the mouth’s cell is constantly replaced. By rigorously swishing a saline solution, cells and the student’s breakfast were retrieved from the lining of the mouth wall.

Afterwards, one milliliter of the saline solution was taken by using a micropipet. The pipetted solution was then transferred into a pipette tube to be centrifuged, a process that separates the solution by the density of the contents. A centrifuge rapidly spins the pipette tube approximately 10,000 times per minute, causing the cells to sink.

After boiling the cells for about 10 minutes, the DNA, cell, and chelex soup was once again centrifuged to separate the DNA from the chelex.

“They enjoy actually performing the lab and being able to see a real world application to the skills they learned in class,” Miss Ross said.

Although there is a large amount of DNA extracted from the cell, there is a relatively small amount of the wanted 400 base pairs of DNA found within the mitochondria. To find the needle in this haystack, Polymerase Chain Reaction (PCR) was used. PCR is a method to find and copy specific pieces of DNA, more specifically the 400 base pairs in the mitochondria.

“I liked how we got to use a variety of skills and tools like gel electrophoresis and micro pipettes,” said Wong.

To ensure the students correctly replicated the DNA, gel electrophoresis was performed on part of the PCR solution. Gel electrophoresis is the process in which the DNA travels through a gel due to an electrical field, as DNA is slightly negative. Under UV light, the DNA lit up as a green color due to the presence of a compound from jellyfish. If the DNA was correctly extracted and copied, a band was supposed to light up around the 400 nucleotide location.

“They generally love this lab,” Miss Ross said. “They think that finding their own sequence is an exciting thing and then being able to compare to their peers, is something they haven’t been exposed to before.”

DNA extraction recipe:  obtain cells from the mouth, strain the cells, boil the cells, and then put in thermocycler for 30 minutes.

Miss Lee added, “Students tend to get excited about being able to analyze their own DNA and finding other students in their class who have the most similarities in their DNA sequence.”

The extracted mitochondrial DNA was then sent to the Cold Spring Harbor DNA Laboratory to be sequenced, so the students can compare their DNA to various ethnicities from around the world, finding their true origins.

“The trip was very interesting because it allowed us to fully experience how to extract our own DNA,” said Kenny Malasarte ‘16.

DNA-1

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