Principles of Biology

ByFrank H. Osborne, Ph. D.

Lab 4 - Enzymes and Digestion

Enzymes and DigestionI. Properties of enzymes A. Enzymes are molecules of protein, which are sometimes associated with electron carriers or metal ions. B. Enzymes cause biochemical reactions to occur at body temperatures. C. Enzymes can be changed by harsh conditions (denaturation).

II. Properties of enzymatic reactions A. Required materials for an enzymatic reaction 1. The substrate is the molecule that reacts with the enzyme. 2. Enzymes require correct conditions of pH and temperature. 3. The enzyme is required or the reaction will not occur.

Enzymes and DigestionII. Properties of enzymatic reactions B. Steps of an enzymatic reaction 1. The enzyme interacts with the substrate which is the starting material. 2. The enzyme changes the structure of the substrate, resulting in formation of the product. 3. The enzyme releases the product.

III. Examples of enzymatic reactions A. General form of an enzymatic reaction enzyme substrate(s) product(s)

1. The enzyme acts on the substrate to produce the product. 2. The enzyme catalyzes the reaction but is not used up.

B. The catalase reaction catalase 2 H2O2 2 H2O + O2

1. The catalase destroys the peroxide producing oxygen gas and heat. 2. A mixture of catalase and water does not react due to the absence of peroxide. 3. Cooking denatures the enzyme so it does not work.

C. The amylase reaction amylase starch maltose1. The amylase digests the starch producing maltose which is a sugar.2. A mixture of starch and water gives a positive starch test but not a positive sugar test because the enzyme was absent.3. A mixture of water and maltose gives a positive sugar test because maltose is a sugar.

C. The amylase reaction amylase starch maltose

3. A mixture of water and maltose gives a positive sugar test because maltose is a sugar but not a positive starch test because starch is absent in maltose solution.

D. The lipase reaction lipase fat glycerol + fatty acids

1. The lipase digests the fat molecules producing glycerol and fatty acids.2. Bile increases the surface area of the fat droplets to make digestion easier.3. Lipase requires a pH of 7.8 which is weakly alkaline.

D. The lipase reaction lipase fat glycerol + fatty acids

4. The presence of fatty acids produced by the reaction lowers the pH of the mixture causing a change in the color of the indicator dye.

E. The pepsin reaction pepsin protein amino acids

1. The pepsin digests protein molecules producing amino acids.2. Pepsin requires a pH of 1.6 which is strong acid.3. Pepsin is adapted to the acidic conditions of the stomach where it digests proteins.

F. The trypsin reaction trypsin protein amino acids

1. The trypsin digests protein molecules producing amino acids. 2. Trypsin requires a pH of 7.8 which is weak base. 3. Trypsin is adapted to the weak alkaline conditions found in the small intestine where it digests proteins.

Test for Catalase:Setup

Test for Catalase:Results

Test for Amylase: Setup

Test for Amylase: Results

Test for Lipase: Setup

Test for Lipase: Results

Test for Protein Digestion

The End

Lab 4Enzymes and Digestion