Problem 100 - A Complete Resource Book in Chemistry for JEE Main

Question

The carbohydrate which cannot be hydrolyzed by the human digestive system is (a) starch (b) cellulose (c) glycogen (d) all of these

Step-by-Step Solution

Answer

(b) cellulose

Step 1: Understanding Hydrolysis

Hydrolysis is a chemical process where a compound is broken down with the addition of water. In human digestion, certain carbohydrates are broken down into simpler sugars via hydrolysis so our bodies can absorb and use them.

Step 2: Identifying Each Carbohydrate

We need to identify which of the given carbohydrates can be hydrolyzed by the human digestive system. Starch is made of glucose units and can be broken down into glucose by human digestive enzymes. Glycogen, similar to starch, is also broken down into glucose. Cellulose, however, consists of glucose units linked by beta-1,4-glycosidic bonds that human enzymes cannot break down.

Step 3: Determining the Non-Hydrolyzable Carbohydrate

Since human enzymes can hydrolyze both starch and glycogen but cannot hydrolyze cellulose due to its beta-1,4-glycosidic bonds, cellulose is the carbohydrate that cannot be hydrolyzed by the human digestive system.

Key Concepts

Human Digestive Enzymes

Human digestive enzymes are vital proteins that speed up the breakdown of food so that nutrients can be absorbed in the digestive tract. These enzymes work at different stages of our digestive system to ensure that proteins, fats, and carbohydrates are efficiently processed.

• In the case of carbohydrates, the primary enzymes involved include amylase, sucrase, maltase, and lactase.
• Amylase starts the digestion of carbohydrates in the mouth by breaking down starch and glycogen into simpler sugars.
• The small intestine further uses specific enzymes to complete carbohydrate digestion into monosaccharides, the simplest form of sugar.

While our body is equipped with enzymes to handle most carbohydrates, certain carbs, such as cellulose found in plant cell walls, remain indigestible because they require a different enzyme our body does not produce.

Beta-1,4-Glycosidic Bonds

Beta-1,4-glycosidic bonds are a type of chemical linkage that connects carbohydrate molecules, forming polysaccharides. These bonds join glucose units in a specific configuration. This configuration is significant because it determines the structural integrity and digestibility of the polysaccharide.

• In cellulose, glucose units are linked by beta-1,4-glycosidic bonds.
• This bond type forms a linear, fibrous structure that is strong and resistant to breakdown by human digestive enzymes.
• Unlike the beta configuration, alpha-1,4-glycosidic bonds, found in starch and glycogen, form structures that our enzymes, like amylase, can readily break down.

Thus, while cellulose provides rigidity and strength to plant structures, it remains undigested as fiber in our diet.

Hydrolysis of Carbohydrates

Hydrolysis of carbohydrates is a chemical reaction that involves the breaking of glycosidic bonds in the presence of water. This reaction is critical in digestion, transforming complex carbohydrates into simpler, absorbable units.

• During digestion, water molecules interact with carbohydrates to cleave their bonds.
• Human enzymes facilitate this process, allowing for the release and absorption of sugars such as glucose.
• However, as mentioned with cellulose, some carbohydrate structures are resistant to hydrolysis due to their unique bond arrangements, like beta-1,4-glycosidic bonds.

Hydrolysis is thus an essential mechanism in ensuring that carbohydrates are broken down into glucose, which is used as a primary energy source by our bodies.