Interactive, scaffolded model
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Students learn the necessary conditions for self-assembly (random motion and molecular stickiness), play with some example models of self-assembling biological structures (quartenary structures such as hemoglobin, fibers, and microtubules), and then design their own self-assembly structures.
Students will be able to:
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Self-assembly is not part of the traditional biology curriculum, but it is a powerful idea relating to many concepts that are. This activity can serve as an engaging introduction. With a teacher’s guidance, students should also be able to generalize from these simple examples to the formation of more complex molecular structures.
For example, after doing this activity, students might be interested in the story of the T4 phage, a virus with a beautiful self-assembling icosahedral capsid. The virus contains just a small amount of genetic material, which seems hardly enough to contain the instructions for building its complex, symmetrical shell, made of thousands of parts; it turns out that these parts are identical monomers that self-assemble.
Another interesting question for class discussion is whether or not everything biological is constructed through self-assembly. You can point out that chemical reactions catalyzed by enzymes are required to form the covalent bonds that hold many structures together. These bonds are much stronger than the charge attractions students see in the activity. You can also describe the role of template-based synthesis (making one nucleotide strand by copying it from another) and of chaperone molecules (which help proteins fold into the right shape by shielding them from the influence of surrounding water molecules).
Self-assembly is the spontaneous formation of organized structures from smaller subunits. Both random motion and interparticle interactions are necessary for it to occur.
Additional Related Concepts
This activity continues to explore ways in which proteins assume their shapes to provide structure and machinery for cells. This makes it a natural extension for the previous Stepping Stone Activity Protein Folding (http://molo.concord.org/database/activities/225.html).