With the short class period, we briefly reviewed the science behind the strawberry DNA extraction solution by watching a segment of the video below (beginning at about the 3:00 mark):
Students then located their DNA samples from yesterday. Although our microcentrifuge stopped working toward the end of 3rd period, students had the opportunity to observe their samples and use laboratory-grade micropipettes to transfer a small volume of their DNA samples to glass slides. The samples were visualized using our class digital microscope connected to the projector for all to see. Students in 2nd and 3rd period were able to compare findings after centrifuging their samples, while students in 4th and 5th periods had more time to prepare and observe samples under the microscope. Notes from the whiteboard, as well as a selection of microscope pictures (some potentially showing several DNA strand clusters and others showing cellular debris with some possible DNA strand clusters), are shown below:
With the Curriculum Fair resulting in shortened class periods, students worked incredibly efficiently in small groups to extract DNA from strawberries. We modified the procedure written the day before such that groups of 4 students worked together to prepare 500 mL of extraction solution using one of the 5 available liquid soap products (450 mL water + 50 mL soap + 1 tsp salt). Each student then extracted DNA from their strawberry and saved an aliquot of the extracted DNA in an Eppendorf tube labeled with the student’s initials which will be used in class tomorrow for further study and analysis.
In our continued study of Central Dogma, we set our sites on extracting DNA from strawberries. To prepare for the lab, students watched two videos explaining the DNA extraction procedure (both produced by the North Carolina Community Colleges group NCBioNetwork.org). The first video, produced 5 years ago, provides students with a straight-forward approach to extracting DNA. Students watched the video and wrote down as many details as they could.
After watching the video, we assembled one class procedure “crowd-sourced” from the all of the student notes. Missing from the original video are some of the details explaining how the reagents in the extraction solution actually work. NCBioNetwork recently reduced a newer version of the video, complete with dramatic effects and a really awful script. Because the content in the newer video added to student understanding, we elected to watch and then updated the class procedure after.
At the end of the second video, students learned that human DNA varies by only 0.1% from person to person. For the final segment of class, students watched a thought-provoking video about a scientist who has combined a variety of tools and technologies to turn DNA from hair into portraits using 3-D printing.
After reviewing the Unit 4 final exams, it was evident students need additional practice writing scientific procedures. Today, students were tasked with watching a short video of DNA extraction from a strawberry, writing a procedure for the experiment, and then working with their table partner to complete the experiment. By having to follow their own procedure, the concept of writing a procedure in enough detail for someone else to follow it was reinforced. Students will use the procedures they wrote today to help them write a related procedure tomorrow. Click here for today’s lesson and review the strawberry DNA extraction video below.