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One of the learning bottlenecks that students often have is recognizing that enzymes identify
and interact with their substrates on the basis of complementary shapes. What makes the shapes complementary is a combination of the surface shapes of the molecules and the distributions of charge and hydrophobicity, but these details are secondary in importance to the basic idea of recognition by shape.
We have built this series of scenarios around two other interesting things. One, which is
amusing to students, is flatulation. Just what causes beans to give people gas? A second interesting thing is lactose intolerance. Why can some people tolerate lactose, while others cannot? These physiological effects result from the interactions of various carbohydrates with enzymes that digest them. If we have appropriate digestive enzymes, then we can take advantage of the carbohydrate. If we do not have appropriate enzymes, then our intestinal bacteria may get the carbohydrate instead. If neither we nor our bacteria have appropriate enzymes, then the carbohydrate passes through undigested--something we euphemistically refer to as fiber.
There are two types of scenarios here. The first includes all four of the carbohydrate types that
we consider, in a single page.
The other three scenarios consiider only three of the four carbohydrate types, derived from
different types of meals. The use of different scenarios among different groups of students is that each group can come to “certainty” that they have understood their scenario. However, a certain degree of cognitive dissonance ensues when the whole-class discussion reveals that different groups have different answers. Resolving this conflict helps deepen the learning of the basic principles.
The first page of diagrams is common for all scenarios; the subsequent pages are alternate versions of “page 2." |
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