Chapter 14

1. Complete the interactive matching exercise to see answers.

2. Our most important foods—lipids, complex carbohydrates, and proteins—are large macromolecules that cannot be taken up by cells of the intestine. They must be converted into small molecules that have transport systems allowing them entry to the cells of the intestine. Once inside the cells, the carbohydrates, fatty acids, and amino acids are processed by metabolic pathways to yield energy or used as building blocks.

3. Chewing well efficiently homogenizes the food, rendering it more accessible to the digestive enzymes.

4. Denaturation is the unraveling of a protein’s three-dimensional structure. The denatured, extended protein is a much more efficient substrate for digestion by proteases.

5. α-Amylase hydrolyzes the α-1,4 bonds, generating limit dextrin, maltotriose, maltose, and glucose. Maltase digests maltose, whereas α-glucosidase digests maltotriose and other oligosaccharides that may have been generated by α-amylase. Dextrinase digests the limit dextrin. The simple sugars resulting from these enzyme activities are absorbed by the intestine.

6. If a small amount of trypsinogen were inappropriately activated in the pancreas or pancreatic ducts, trypsin could activate other zymogens and lead to the destruction of the pancreas.

7. Macaroni is starch. Hydrating the starch enables α-amylase to more effectively bind to the starch molecules and degrade them.

8. Unlike proteins and carbohydrates, neither lipids nor the products of lipid digestion—fatty acids—are water soluble. The lipids are converted into mixtures of lipid droplets and water (emulsions), a conversion enhanced by bile salts. The emulsions are accessible to lipases. The fatty acids generated by the lipases are carried in micelles to the intestinal membrane.

9. The formation of emulsions allows aqueous lipase access to the ester linkages of the lipids in the lipid droplets.

10. Lipid digestion and absorption would be hindered, and much lipid would be excreted in the feces.

11. Micelles transport the products of lipase digestion, fatty acids and monoacylglycerol, to the intestinal cells for absorption.

12. Secretion of the digestive enzymes as precursors reduces the likelihood that the secretory tissue will be damaged by its secretory products.

13. CCK stimulates the secretion of digestive enzymes by the pancreas and the secretion of bile salts by the gall bladder.

14. Sodium, in cooperation with the sodium-glucose linked transporter, will allow entry of glucose into the intestinal cells.

15. Activation is independent of zymogen concentration because the reaction is intramolecular.