Humans produce the enzyme amylase. This enzyme breaks down starch, a complex carbohydrate found in many food sources (e.g.. potatoes, breads). Explain why the human digestive system is unable to use amylase to break down the complex carbohydrate cellulose, which is also found in some foods (such as celery).
The correct answer and explanation is :
Answer:
The human digestive system is unable to use amylase to break down the complex carbohydrate cellulose because amylase specifically targets alpha-1,4-glycosidic bonds in starch, while cellulose consists of beta-1,4-glycosidic bonds, which amylase cannot break. Humans lack the enzyme cellulase, which is required to hydrolyze these beta bonds.
Explanation:
Carbohydrates are made up of long chains of glucose molecules linked together by different types of glycosidic bonds. The digestibility of a carbohydrate depends on the enzyme’s ability to recognize and break these bonds.
1. Starch and Amylase Activity
- Starch is a polysaccharide found in foods like potatoes and bread.
- It consists of glucose molecules connected by alpha-1,4 and alpha-1,6 glycosidic bonds.
- The enzyme amylase, found in saliva and the pancreas, is designed to hydrolyze these alpha bonds, breaking starch into simpler sugars such as maltose and glucose, which can then be absorbed into the bloodstream.
2. Cellulose and Why Humans Cannot Digest It
- Cellulose, found in plant cell walls (e.g., celery, lettuce), is also made of glucose molecules.
- However, its glucose units are linked by beta-1,4-glycosidic bonds, which are structurally different from the bonds found in starch.
- Human amylase cannot break these beta bonds because its active site is not shaped to recognize them.
- Unlike some herbivores (e.g., cows, termites), which have cellulase-producing microbes in their gut, humans lack the enzymes necessary to digest cellulose.
3. Consequence of Cellulose in the Human Diet
- Since cellulose remains undigested, it acts as dietary fiber, aiding digestion by adding bulk to stool and promoting bowel movements.
- Even though we cannot extract energy from cellulose, it plays a vital role in maintaining gut health.