1. PhysioEx 39B
Dr. Kim Wilson

2. Objectives
To list the digestive system enzymes involved in the digestion of proteins,fats, and carbohydrates; to state their site of origin; and to summarize the environmental conditions promoting their optimal functioning.
To recognize the variation between different types of enzyme assays.
To name the end products of digestion of proteins, fats, and carbohydrates.
To perform the appropriate chemical tests to determine if digestion of a particular food has occurred.
To cite the function(s) of bile in the digestive process.
To discuss the possible role of temperature and pH in the regulation of enzyme activity.
To define enzyme, catalyst, hydrolase, substrate, and control.
To explain why swallowing is both a voluntary and a reflex activity.
To discuss the role of the tongue, larynx, and gastroesophageal sphincter in swallowing.
To compare and contrast segmentation and peristalsis as mechanisms of propulsion.

3. Chemical Digestion of Foodstuffs: Enzymatic Action
Food digestion is a prerequisite to food absorption so nutrients can be absorbed.
Enzymes are large protein molecules produced by body cells.
Enzymes act as catalysts - increase the rate of a chemical reaction without becoming part of the product.
Hydrolases- break down organic food molecules, or substrates, by adding water to themolecular bonds, thus cleaving the bonds between the subunits or monomers.

4. Activity 1
In this experiment you will investigate the hydrolysis of starch to maltose by salivary amylase, the enzyme produced by the salivary glands and secreted into the mouth.
Starch decreases and sugar increases as digestion proceeds according to the following equation:
amylase
Starch + water  X maltose

5. Activity 1 cont.
Because the chemical changes that occur as starch is digested to maltose cannot be seen by the naked eye, you need to conduct an enzyme assay, the chemical method of detecting the presence of digested substances.
You will perform two enzyme assays:
IKI assay - detects the presence of starch
Benedict’s assay - tests for the presence of reducing sugars, such as glucose or maltose, which are the digestion products of starch.

6. Activity 1

7. Protein Digestion by Pepsin
The chief cells of the stomach glands produce pepsin - a protein-digesting enzyme.
Pepsin hydrolyzes proteins to small fragments (polypeptides and a few free amino acids).

8. Activity 3
In this experiment, you will use BAPNA, a synthetic “protein” that is transparent and colorless when in solution.
If the solution turns yellow if the enzyme digests the BAPNA substrate; it remains colorless if pepsin is not active or not present.

9. Activity 3

10. Fat Digestion by Pancreatic Lipase and the Action of Bile
Fats and oils require pretreatment with bile to physically emulsify the fats. Occurs in 2 reactions:
bile
Fats/oils → minute fat/oil droplets
(emulsification)
lipase
Fat/oil droplets → monoglycerides and fatty acids

11. Activity 4 cont.
You will be using a pH meter in the assay cabinet to record the drop in pH as the test tube contents become acid
Some of the end products of fat digestion (fatty acids) are organic acids that decrease the pH provides an easy way to recognize that digestion is ongoing or completed.

12. Activity 4

13. Instructions Go to Exercise 39B in the back of the Marieb lab manual.
Read the information preceding Activity 1.
Insert the PhysioEx CD and select Exercise 8: Processes of Digestion, then Amylase.
Complete Activity 1: Assessing Starch Digestion by Salivary Amylase (Incubation and Assays).� Record your results in the chart for Activity 1 in the Questions Section, then answer the remaining questions for Activity 1 in the Questions Section.
Read Protein Digestion by Pepsin to Activity 3.
Choose Pepsin from the Experiment menu.
Complete Activity 3: Assessing Protein Digestion by Pepsin (Pepsin Incubation and Pepsin Assay).� Record your results in the chart for Activity 3 in the Questions Section, then answer the remaining questions for Activity 3 in the Questions Section.
Read Fat Digestion by Pancreatic Lipase and the Action of Bile to Activity 4.
Choose Lipase from the Experiment menu.
Complete Activity 4: Assessing Fat Digestion by Pancreatic Lipase and the Action of Bile (Lipase Incubation and Lipase Assay).� Record your results in the chart for Activity 4 in the Questions Section, then answer the remaining questions for Activity 4 in the Questions Section.