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."