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Principles of Biology
By
Frank H. Osborne, Ph. D.
Lab 4 - Enzymes and Digestion
Enzymes and Digestion
I. 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 Digestion
II. 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
maltose
1. 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 4
Enzymes and Digestion