A layer out from that I hypothesized that students probably didn't understand a well-accepted scientific model: the fluid mosaic model of the phospholipid bilayer membrane. Irrelevant? Maybe. Except all living things have membrane systems. And teaching about membranes is central to biology. And membranes have been illustrated, modeled, and "visualized" in a million contexts including in our last lecture this week.
My final hypothesis: that building a 3-D model of a membrane would be a hard task for my students. I couldn't do it myself, the first ten times I tried.
I set my students to work first, by asking them to read one of my posts called "Permeability: just for cell membranes?" In that post I discuss lots of concepts of permeability, way beyond biology. I asked students to respond and if you go to that post you can see how they did. Pretty amazing actually.
Next I asked students to connect the two concepts of permeability and evolution. A steep task but one that they lit nicely to.
The major task of the day was for students to build a model of a membrane using Zometools, a wonderful toy I've been itching to introduce.
Here are my findings. Students were intent upon depicting phospholipids. They did so quite literally, modeling the phosphate head and the hydrocarbon tails. Many wanted to depict both the saturated hydrocarbon tail and the unsaturated one. Some even wanted to include the glycerol that glues the two together.
A moment of liberating fresh air came when I told my students they could look at the big picture and go abstract. They could represent the bilayer any way they wanted. Here they divided into two approaches: those who went 3-D and those who used the Zometools like colored lines flat on the lab bench surface.
The next challenge was depicting the embedded proteins. We haven't studied proteins yet so it's no surprise many of the proteins depicted were just a single line. But it's worth it to mention I asked students to google images of membranes and refer to them, so anyone could have seen that the proteins have dimensional and not just linear qualities.
Many students showed the proteins embedded horizontally, swimming between the two layers of phosphipids. This in spite of the fact that they were working off of lecture notes they had drawn as well as google images.
Those students who depicted proteins arranged vertically did not show the proteins reaching past the phosphate heads, a biologically important feature. And the groups who did almost everything "right" were limited by the fact that their models presented a facies (just like I showed them in lecture!), just a slice of the cake, and not a whole sheet cake of membrane.
An aha moment came when one student wore his Halloween sombrero to class. I suggested, what if we put two sombreros together and called the head part a protein?
Then I learned. Instruct the 2-D students to go 3-D. Instruct the protein people to orient their proteins vertically, to extend them beyond the structure of the bilayer, and bulk up the proteins. To those students who made a wonderful "slice" model I suggested: make three more of these, arrange them like four walls of a house, and build a protein up through the middle.
Here are some of the results. I'm very happy with them! Next week we're building enzymes in lab to illustrate the lock and key active site. I'll ask these intrepid and intelligent students to make their proteins ten times the size of the substrate...about the size of a person. I have a feeling they'll impress me again.
