Enzyme Activity in the Digestive System
Catalyst: a substance that speeds up the rate of a chemical reaction without being changed or used up by the reaction
Enzyme: Special protein molecule that acts as a catalyst in biological systems. Enzymes require a specific temperature and pH to function correctly.
Without enzymes, life could not exist.
Thousands of chemical reactions go on in a living cell every second, each catalyzed by its own specific enzyme.
Enzymes speed up reactions by binding to the reactants known as substrates(e.g. food).
Notice that the normal reaction requires a higher activation energy which would correspond to a high body temperature. This is usually not possible in living organisms.
The enzyme-catalyzed reaction has lower activation energy. This lower activation energy would correspond to body temperature, but is only possible in the presence of an enzyme.
Enzymes are named after the reaction that they catalyze.
Their names usually end in “ase”.
e.g. lipase – breaks down lipids
sucrase –breaks down sucrose
amylase – starch (“amylose”)maltose
pepsin-proteins amino acids
peptidase –proteinsamino acids
Analyzing Enzyme Action
One common enzyme found in animals is called catalase. An identical enzyme called peroxidase is found in plants. Peroxidase decomposes harmful hydrogen peroxide produced by metabolism to water and oxygen. Another common enzyme is lactase. Those of you who are lactose intolerant may have heard of this second enzyme. Lactase cuts lactose into glucose and galactose. A third enzyme called amylase is secreted in the saliva. Salivary amylase breaks down starch into maltose. The purpose of this activity is to show the action of these three different enzymes and some factors that affect them.
A: The Effect of Peroxidase on Hydrogen Peroxide
1. Set up 3 test tubes as follows:
a) 10 mL of 3% hydrogen peroxide + 10 drops of water
b) 10 mL of 3% hydrogen peroxide + 10 drops of 0.1 M HCl (aq)
c) 10 mL of 3% hydrogen peroxide + 10 drops of water
2. Potato is a ready source of peroxidase. Add a 2 cm long cylinder of raw potato to test tubes a) and b). Add 2 cm long cylinder of cooked potato core to test tube c).
3. Record height of the fizz after 3 minutes.
4. Summarize results in a suitable table of your design.
B: The Effect of Lactase on Milk
1. Add the following samples to 3 wells on a spot plate:
a) 1 dropper of 2% milk
b) 1 dropper of 2% milk + 1 DROP of Lactaid
c) 1 dropper of Lacteeze 2% milk
2. Using tweezers, dip one piece of glucose test paper into each sample and then place on paper towel. Record colour after 60 s and compare to standard colours on package to determine glucose content.
3. Summarize results in a suitable table of your design.
C: Saliva and Starch
1. Obtain an unsalted soda cracker. Put the cracker in your mouth and chew it for 3 minutes. You may chew but do not swallow.
2. Record any changes in flavour.
3. Help yourself to a drink of water to rinse out your mouth.
Analysis
1. Write the word equations for the above three reactions.
2. What effect did the potato peroxidase have on the hydrogen peroxide?
3. What effect does acid have on the rate of the reaction of peroxidase?
4. What effect does cooking the potato have on the rate of the reaction? Suggest a reason for this observation.
5. Compare the glucose content of the three different samples of milk.
6. How would milk be expected to taste differently after adding the enzyme lactase? Explain.
7. What change in flavour occurred while the cracker was being chewed in the mouth? What compound would account for the change in flavour? What chemical changes occurred that would explain the change in flavour?
8. Summarize this activity by listing the enzyme, substrate and products of each reaction. Organize this summary in the form of a table.