Your students might have heard that their stomachs use enzymes to break down food, but they may not understand how they work. Enzymes are a special class of proteins that can attach themselves to particular molecules and actually pull on it, stretching the bond that holds the molecules together, a part of digestion. Enzymes, however, are very fragile and break down soon after they are formed. For this reason, people must a regular supply of protein.
To illustrate just how fragile an enzyme can be, you can perform this demonstration. You will need some fresh pineapple (not canned), a blender, three bowls and Jell-O gelatin (It doesn't matter what flavor.)
Take some pieces of the fresh pineapple (skin removed) and crush it in the blender until it is a thick pulp.
Prepare the Jello, following the directions on the package until you get to the point where you need to put it in the refrigerator.. Take about a tablespoon of the pulpy mixture and put it into one of the bowls. Pour about 1/3 of the Jello to the bowl and stir it around. Mark this bowl as Room Temperature Pineapple.
Take the rest of the pineapple pulp and heat it on the stove on high for about 3 minutes, stirring constantly. Take about one tablespoon of this mixture and put it in the second bowl. Pour 1/3 of the Jello mixture on top and stir. Label this Heated Pineapple.
Pour the rest of the Jello into the third bowl and label it Control.
Put them all in the refrigerator for a few hours.
After a Few Hours
The control bowl should, of course, look like regular jello.
The bowl marked room temperature pineapple should, on the other hand, be as runny as it was when you put it in the bowl. Pineapple contains an enzyme that stops the reaction which causes jello to gel. You may have noticed that Jell-O warns of this reaction on the side of their boxes, and suggests that you do not use fresh pineapple (as well as a few other fruits).
The bowl marked heated pineapple should look pretty much like the control jello.
The heat that was added to this pineapple was enough to destroy the enzyme
This is also why you can use canned pineapple in jello. The enzyme has been destroyed during the pineapple's processing.
Because enzymes are so fragile and break down soon after they are formed, new enzymes, made from protein have to replace the old ones in a continual process. This is one reason why it is so important to have protein regularly in our diet.