Part A Lab Report: DNA Structure

For future reference - click on the picture which links to the related post.

And here's a student lab sheet. This is the one where I asked the students to compare the model to reality. Interestingly, today we viewed a portion of the PBS/NOVA video: Cracking the Code of Life. The scientist in the opening scenes doesn't do such a good job of describing how DNA is different from the 3D model being displayed by the program's host. (Don't ask me for names, it's been a long week!)

UPDATE: The scientist is Eric Lander, Director of the MIT Center for Genome Research, and the correspondent is Robert Krulwich, whom you may remember as an ABC Nightline correspondent. Lander does note that the model looks like DNA in a "cartoon" sort of way, but doesn't elaborate.

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The kids still have a hard time with the concept of scale. The student here is trying to express an idea we discussed in class, but she doesn't completely understand it yet. Namely, in one sense our model is much bigger than real DNA, in an obvious sense. In another sense, it is much smaller - we have only 5 base pairs in our model, where a single strand of DNA contains 10's of millions of base pairs. If our model had that many base pairs (using pasta & pipe cleaners) it would be over 1000 miles long! We actually did the math on this in class. Some of the students totally misinterpreted this number - "Wow, you mean we have 1000 miles of DNA in one cell" Well, no, if we enlarged a strand of DNA to the size of our model, it would be 1000 miles long...etc. Actually the fact that the DNA in one cell laid end to end would equal about 2 meters is pretty mind boggling in itself. Just multiply that 2 meters by the 50 trillion or so cells in our bodies, and that's a pretty significant distance also! (100 trillion meters = 100,000,000,000 Km = 62,000,000,000 miles roughly).

I probably went overboard with some of the DNA material, but it's hard to gauge how far to take it. The last exam (January 2005) is pretty heavy on the genetics material, I plan on using the questions for their unit test tomorrow. We'll see how they do.

UPDATE