Cells use enzymes internally to grow, reproduce, and create energy, and they often excrete enzymes outside their cell walls as well. For example, E. coli bacteria excrete enzymes to help break down food molecules so they can pass through the cell wall into the cell. Some of the enzymes you may have heard of include:

• Proteases and peptidases - A protease is any enzyme that can break down a long protein into smaller chains called peptides.
• Amylases - Amylases break down starch chains into smaller sugar molecules. Your saliva contains amylase and so does your small intestine.
• Cellulases - Cellulases break cellulose molecules down into simpler sugars. Bacteria in the guts of cows and termites excrete cellulases, and this is how cows and termites are able to eat things like grass and wood.

What do you notice about all the words enzymes in the list above? With some exceptions, the names of enzymes end in "-ase." The name depends on their role in the metabolic process and the substrate they interact with. For example, the enzyme that breaks down the sugar sucrose is called sucrase. Below is a chart of some more common enzymes and the substrates they act upon.

Watch the following video to see enzymes at work!

Answer the following questions in your notes.

1. What caused the apple to turn brown?
2. What did the video suggest you do to prevent the apple from turning brown?
3. What other fruits are affected by the action of enzymes?