For this part of my class tech project, I had students use an online site to learn more about DNA. A corresponding worksheet was provided by the Bio 10 team.
Image is the courtesy of the Image Library of Biological Macromolecules based in Jena, Germany, at http://www.ucmp.berkeley.edu/glossary/gloss3/dna.html.
My classes had already studied DNA's structure and almost all students were able to draw a perfect 2-dimensional DNA molecule containing six nucleotides. This activity was intended to give them a deeper understanding of DNA's structure before we moved on to observe replication of DNA. This assignment had an closed part (the worksheet) that requested students to sketch what they saw and an open part (my project) that asked students to comment on their learning. My objective was to evaluate their learning and evaluate the site for future use during the DNA unit.
The site represented a DNA molecule in a three-dimensional projection. Individual chemical radicals (nitrogenous bases, sugar/phosphate backbones, and hydrogen bonds) could be 'amplified' to make them look fatter. Elements were color-coded so they were easily spotted. The molecule could be rotated for viewing from any angle. The molecule could also be set to automatically rotate through 90 degrees. Individual base pairs could be amplified or closer observation. And a click could make all external hydrogen atoms disappear, to make the molecule appear less cumbersome.
After the unit was completed, I asked the students to comment specifically on their learning and to vote if they felt I should use the unit again next year. 62 of 73 students recommended I use this activity again next year for the DNA unit.
Some specific student comments of their learning included:
It showed how the nitrogen bases are perpendicular to the sugars
Helped see where hydrogen bonds are broken for replication (not intended to show this).
From top can see that hydrogen bonds occupy the center
Easier to understand with any angles and highlighting of parts we selected.
Color of elements made it easy to understand
DNA is more complex than what we learned
Twisting together
Color coding
That phosphates contain oxygen
Nitrogen bases next outside ring to hydrogen bonds
The elements of the atoms of DNA
I saw the purine (two rings) and pyrimidine base
If one of the components is missing it might cause a mutation
Hydrogen and nitrogen connect…the side of DNA backbone
Zooming the picture made me see more clearly
The complexity is much greater than I thought
Better understanding what is meant by “double helix”
Different kinds of chemical bonding
Surface is rough, rather than straight
Viewing the DNA strands from the top,…sugar and phosphate appears on the outside
How many hydrogen bonds were formed at each part of DNA
The “Spin” feature ..was very fascinating
How that structure we drew on the quiz actually becomes a helix…a lot more complex
O – N (oxygen and nitrogen) and N – N (nitrogen and nitrogen) form hydrogen bonds
At the outer part of the DNA there is a lot of oxygen and phosphorus
Carbon was the atom [that] DNA contained the most
Students learned considerably more than I had expected. The depth of students understanding helped them with comprehending the replication lessons that followed. The best students were able to get a lot more out of this open-ended lesson:
“I already knew about the exact configuration of the nucleotides, but I did not have an idea how it curved around itself in its double helix shape, specifically how its shape is created with molecules. I noticed how the two nucleotide strands twisting around teach other help to protect the base-pairs in between them. On the molecular level of the base pairs, I noticed how the pairing, A-T C-G, works perfectly with the molecules designed to fit each other.”— T. E. (name withheld)
I will use this lesson in the future.
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