Meet Charlene “Charlie” McCord! She is a PhD candidate at the University of Chicago and ichthyologist (a scientist who studies fishes). She is also a popular and frequent visitor to Sisters4Science classrooms, and we were so excited to have her at Woodson!
As an ichthyologist, Charile spends a lot of time extracting fish DNA, and for her lesson February 21, 2014, she challenged Brianna and Ashanta (both of which have perfect attendance) to extract strawberry DNA.
Before the lesson, the girls were given the additional challenge of being “excellent communicators” by their STEM Facilitator, Tolu Rosanwo. If they asked questions, paid close attention and communicated well, they would be awarded with their first digital badge. These badges can be seen on their parents’ cell phones as well as kept until their entrance into high school, college or beyond.
Charlie began her lesson with asking the girls about DNA. Brianna said that,”DNA tells people apart,” and Ashanta asked, “Don’t we get it from our parents?”
“Correct!” Charlie said, and she went on to explain that strawberries have a lot of DNA. Human beings are diploid organisms with 2 copies of each chromosome while strawberries are octaploid and have 8 copies their DNA! That’s a lot, and makes DNA extraction possible in a middle school classroom!
Charlie also told the girls that DNA is found in the nucleus of the cell, and there are several barriers to getting them out: namely the cell wall and the nuclear membrane.
To crush the cell wall, the girls pulverized the strawberries with their hands.
Once smashed, the girls squeezed the smooth strawberry remains into a cup, which they THOROUGHLY enjoyed doing.
Ashanta squeezes the smooth strawberry puree into a cup.
Then, Charlie instructed Brianna and Ashanta to add soap. Soap, which has both hydrophobic (water-fearing) and hydrophilic (water-loving) properties, can break down the membranes that stand between them and the DNA.
After adding the soap, the the strawberry mix forms 2 layers. Then, rubbing alcohol was added in order to precipitate DNA from the solution.
Alcohol added to the soap/strawberry mixture precipitates DNA
Brianna and Ashanta as well as their STEM Facilitator were so amazed by the fact that they could pull out strawberry DNA from a cup!
Pulling DNA out of a cup!
That day, Brianna and Ashanta learned that DNA extraction isn’t easy, but Charlie stressed that strawberry DNA extraction was much easier than fish DNA extraction. She encouraged the girls to try this experiment out at home, and asked them to think scientists saying, “How would you change this experiment?” They said they would try using laundry detergent or even a different fruit.
In her journal entry, Brianna wrote: “I used to think it getting to DNA was easy from all the crime shows I watched but now I know it doesn’t because when we destroyed the strawberry we smushed, add soap, add water, add alcohol and DNA floated up.”
Brianna’s journal entry
The girls were all smiles at the end of the day! Thanks, Charlie and good luck as you complete your PhD program! Brianna and Ashanta were wonderful communicators that day and were rewarded with their first digital badge!
Hugs at the end of the day!