Digestive Enzymes Introduction: A person is eating a food item. The food contains 30 grams of starch (a polysaccharide), 30 grams of protein and 30 grams of triglycerides (a lipid). Samples of digestive juices are taken during the digestive process and tested to monitor the progress of chemical digestion. The locations samples and the results of the testing are provided below. Data Table: Source of Tested Material 1. Bolus in Mouth 2. Bolus in Esophagus 3. Chyme from Stomach 4. Chyme from Proximal Duodenum. Chyme from Distal Duodenum 6. Residue from Ileum 7. Defecated Residue Starch Disaccharide * Protein Amino Acid, di- and tripeptide * Triglyceride (Grams) Fatty Acid and Monoglyceride 2 g g 30 g 0 g 28 g 2 g 20 g 10 g 30 g 0 g 27 g 3 g 20 g 10 g 20 g 10 g 26 g 4 g 10 g 20 g 10 g 20 g 10 g 20 g g 10 g g 10 g g 10 g 0 g 2 g 0 g 2 g 0 g 2 g 0 g 0. g 0 g 0. g 0 g 0. g * Disaccharide, di- and tripeptide units are further broken down to monomers on the brush border of the small intestine before they are absorbed. 1
Carbohydrate Digestion: Graph the levels of the two types of carbohydrates below. 30 Amount 2 of 20 Carbs. 1 10 0 1 2 3 4 6 7 Sample Locations 1. One important enzyme that converts starch into glucose is amylase. Based on the graph, where in the body is amylase active? 2. Based on this data, what secretions must contain amylase? 3. Why did the amount of starch stay the same from sample 2 to sample 3? 2
Protein Digestion: Graph the levels of protein and amino acids/di- and tripeptides below. Amount of Prot/AA 30 2 20 1 10 0 1 2 3 4 6 7 Sample Locations One enzyme that digests protein is pepsin. This enzyme can only work at a ph of 2. Three other protein digesting enzymes such as trypsin are present in the digestive tract. These enzymes work at a neutral ph. Look at the graph: 4. At what location(s) is pepsin working?. Based on this data, what secretion must contain pepsin? 6. At what location(s) are the other protein digesting enzymes such as trypsin working? 7.Based on this data what secretion must contain the protein digesting enzymes such as trypsin? 3
Lipid Digestion: Graph the levels of the triglycerides or monoglycerides and fatty acids below. Amount of Lipids 30 2 20 1 10 0 1 2 3 4 6 7 Sample Locations The enzyme that converts triglycerides into glycerol and fatty acids is lipase. Bile is also necessary for lipid digestion. Bile, produced by the liver and stored in the gall bladder, mixes with lipids and emulsifies them. When lipid drops become emulsified, they are converted into many small droplets. 8. How will this change benefit chemical digestion? 9. Based on your data, at what stage was bile added to the lipid? 10. Based on the graph, where in the body was lipase most active? 11. How can you tell? Based on this exercise: 12. Why did the levels of all monomers, dimers and trimers (simple organic molecules) first increase, then decrease during digestion? As the simple organic molecules were released from macromolecules, they were absorbed. 4
13. What digestive organ(s) are most important for: a) production of chemicals for carbohydrate digestion? b) production of chemicals for protein digestion? c) production of chemicals for lipid digestion? d) - absorption? 14. Why did the monomer content of the food continue to decrease as the material passed through the large intestine? Thinking Questions: 1. Chewing is often difficult for the very young and the very old. Explain how lack of teeth would affect the chemical digestion processes reviewed in this exercise. 16. One medical procedure used to treat morbid obesity is the surgical removal of part of the stomach. Explain how this would affect chemical digestion. 17. Removal of the gall bladder is another common medical procedure. Explain how the absence of this organ from the body would affect chemical digestion.
18. A person with a severe form of Crohn s disease is told by their physician that they need surgery, specifically the removal of most of the jejunum and ileum. Based on the information in this exercise, will the absence of these sections of the small intestine significantly affect chemical digestion? Why or why not? 6