Complexity underlying enzymes can be difficult for students to grasp because
enzymes cannot be readily visualized, and school texts tend to describe them
in abstract molecular terms. One way for achieving a good level of
understanding is to participate to an activity that mirrors the biochemical
practice. I have chosen amylases, two enzymes whose catalytic activity can
be detected without any instruments except the eyes, using the Lugol method.
Moreover they can be easily extracted from germinating barley or the
students' own saliva. Starch hydrolysis can be achieved either by inorganic
catalysts -which require extremes of temperature and pH- or by our extracts -which perform the same reaction under very mild conditions. By considering
this stark difference, students can hypothesise that in living organisms are
present special and powerful substances
, able to catalyse reactions. Then
with some easy, quick and inexpensive laboratory experiments, based on
enzymatic units determination (hydrolysed starch µg/min), students grasp
what the activity of an enzyme consists of. They can observe the influence
of environmental factors (pH, temperature, substrate concentration,
inhibitors presence) on activity, and realise that enzymes are molecular
sensors with catalytic power. The heuristic laboratory approach is
integrated with theoretical knowledge about amylases and starch, their
physiological meaning and biotechnological applications.
