Digestive Enzyme Lab
Introduction: Enzymes catalyze reactions that normally would not take place fast enough at normal body
temperature. Specific enzymes catalyze specific reactions. Digestive enzymes help break food molecules
into simpler substances so that they can be utilized by the body.
Organ
Mouth
Esophagus
Stomach
Small Intestine
Mechanical Digestion
Grinding
Crushing
Moistening
Moistening
Crushing
Grinding
Moistening
Absorption of Liquids
Absorption of simple
sugars
Fat Emulsification
Food Absorption
Starch
Chemical Digestion
salivary amylase
Maltose
Proteins
Starch
pepsin
Polypeptides
pancreatic amylase
Maltose
Disaccharides maltase, lactase, sucrose Monosaccharides
Protein
trypsin, chymotrypsin
Polypeptides
Fats
Large Intestine
peptidase
lipase
Polypeptides
amino acids
Fatty acids & glycerol
Water Absorption
Part 1: Chemical Digestion of Proteins
Proteins are long chains of amino acids. Strong bonds called peptide bonds hold these chains
together. Protein digestion begins in the stomach where pepsin breaks proteins into smaller chains called
peptides. Digestion of proteins continues in the small intestine where the polypeptide chains are further
broken down into amino acids by peptidases. The amino acids are absorbed through the villi that line your
small intestine and are transported to your cells in the blood stream. Your cells put them back together in
different sequences depending on the type of protein needed by the cell.
Foods such as egg white (albumin), legumes and meats are rich in proteins. Pepsin works best in
an acidic environment. In this experiment, we will use hydrochloric acid (HCl) to create the acidic
environment favorable for pepsin actions.
Procedure:
1. Label 4 test tubes with the numbers1, 2, 3 and 4. Put your group number on each test tube.
Tube #
1
2
3
4
Albumin
2 ml
2 ml
2 ml
2 ml
Water
4 ml
2 ml
2 ml
-----
HCl (Caution)
---2 ml
----2 ml
Pepsin
------2 ml
2 ml
Total Volume
6 ml
6 ml
6 ml
6 ml
1. Place all four test tubes in the water bath at 37 Degrees C for 10 minutes. Record observations.
Part 2: Chemical Digestion of Carbohydrates.
Chemicals in saliva help to break down food in our mouths. Saliva contains an enzyme,
Amylase, which begins the chemical process of digestion. Enzymes are molecules that catalyze (bring
about) chemical reactions. Each enzyme is specific to a certain chemical reaction. Amylase catalyzes the
breakdown of starch into sugar. A catalyst is a substance that enables a chemical reaction to proceed at a
faster rate than otherwise possible.
Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as
they are chewed because amylase turns some of their starch into sugar in the mouth.
In this lesson, amylase (an enzyme), which is commonly found in saliva, will be added to cause
the breakdown of the starch . As the reaction progresses, less starch will be present and more sugar
(maltose) will be formed.
The reaction of amylase will be observed by using iodine, which reacts with starch to form a
dark brown/purple/blue/black color (color intensity may vary based on the concentration of
the iodine and the amount of starch present). Usually iodine has a red-brown color. But when it contacts
starch, iodine will turn a dark purple. As amylase breaks down starch, less and less starch will be present
to react with the iodine and the color of the iodine solution will not darken to purple (because sugar
molecules do not react with iodine).
The reaction of amylase will also be observed using Benedict’s solution. The color of the
solution is aqua when glucose is absent. The color goes from green to red-orange the more concentrated
the sugar is.
Blue color
No sugar present
Green color
Low sugar present
Yellow color
Medium sugar present
Orange color
Medium sugar present
Red color
High sugar present
Procedure:
1. Label 4 test tubes 1, 2, 3, 4. Also include your group number on the label.
Tube #
1
2
3
4
Water
2 ml
------2 ml
Cornstarch
2 ml
2 ml
2 ml
-----
Amylase
---2 ml
2 ml
-----
Glucose
---------2 ml
Iodine
0.5 ml
0.5 ml
-------
Benedict’s
------1 ml
1 ml
Total
Volume
4.5 ml
4.5 ml
5 ml
5 ml
**Note: Test tubes 1 and 2 are testing for starch. So information in paragraph above to determine if
starch is present. Do not place test tubes 1 and 2 in water bath!
***Test tubes 3 and 4 should be placed in a boiling water bath for 2 minutes. Use the color chart
above to determine if glucose is present.
Part 3: Chemical Digestion of Fat
Lipids include fats, such as butterfat and oils. Lipids are digested by pancreatic lipase in the
small intestine, a process described by the following two reactions:
1. fat
fat droplets (bile emulsifier)
2. fat droplets + water
glycerol + fatty acids (lipase enzyme)
The first reaction is not enzymatic. It is an emulsification reaction in which fat is physically
dispersed by the emulsifier (bile) into small droplets. The small droplets provide a greater
surface area for enzyme attack. Lipids are hydrophobic and therefore insoluble, so they are
hydrolyzed slowly unless an emulsifier is used. As a result, when the fat droplets are
exposed to an enzyme and broken down into glycerol and fatty acids, the pH of the solution
will go down.
Procedure:
1. Label the tubes #1, 2, 3, 4. Also label each of the tubes with your group number.
Tube #
1
2
3
4
Oil or Cream
2 ml
2 ml
2 ml
2 ml
Water
3 ml
2 ml
1 ml
----
Pancreatin
------2 ml
2 ml
Bile salt
---1 ml
---1 ml
2. Place the tubes in a warm (37oC) water bath for 15 minutes.
3. Record color changes in your data table.
Universal
Indicator
0.5 ml
0.5 ml
0.5 ml
0.5 ml
Total
Volume
5.5 ml
5.5 ml
5.5 ml
5.5 ml