Problem 86 - A Complete Resource Book in Chemistry for JEE Main

Question

Amylose and cellulose both are liner polymers of glucose. The difference between them is (a) Amylose has \(\beta(1 \longrightarrow 4)\) linkage and celulose has \(\beta(1 \longrightarrow 6)\) linkage (b) Amylose has \(\alpha(1 \longrightarrow 4)\) linkage and cellulose has \(\alpha(1 \longrightarrow 6)\) linkage (c) Amylose has \(\alpha(1 \longrightarrow 4)\) linkage and cellulose has \(\beta(1 \longrightarrow 4)\) linkage (d) Amylose has \(\beta(1 \longrightarrow 4)\) linkage and cellulose has \(\alpha(1 \longrightarrow 4)\) linkage

Step-by-Step Solution

Answer

The correct answer is (c).

Step 1: Identify Structure of Amylose

Amylose is a linear polymer of glucose, a component of starch. It is characterized by having glucose units connected through the \( \alpha(1 \longrightarrow 4) \) glycosidic bonds. This defines its helical structure, which is distinct from cellulose.

Step 2: Identify Structure of Cellulose

Cellulose is also a linear polymer of glucose, but it differs from amylose due to its \( \beta(1 \longrightarrow 4) \) glycosidic linkage. These beta linkages form straight, rigid chains, contributing to cellulose's role in plant cell walls.

Step 3: Compare the Linkages

Based on the identified structures: amylose has \( \alpha(1 \longrightarrow 4) \) linkages and cellulose has \( \beta(1 \longrightarrow 4) \) linkages. This aligns with option (c) in the given options.

Step 4: Select the Correct Option

Out of the options provided, (c) correctly represents that amylose has \( \alpha(1 \longrightarrow 4) \) linkages and cellulose has \( \beta(1 \longrightarrow 4) \) linkages. Therefore, (c) is the correct answer.

Key Concepts

Amylose Structure

Amylose is a fascinating molecule, mainly because it is a vital component of starch, which is found in many plants. Its structure is quite unique. Amylose is composed of a long chain of glucose molecules. These glucose units are linked together by special bonds known as \( \alpha(1 \longrightarrow 4) \) glycosidic bonds.
This linkage introduces a curve into the chain. Consequently, amylose forms a helical structure. This particular formation is essential for its function in energy storage in plants. It allows the amylose chains to coil tightly, making it compact and efficient. This structure is why amylose can hold considerable amounts of glucose in a small space, ideal for storage purposes. As a result, amylose plays a crucial role in our diet as a source of carbohydrates, fueling our bodies with energy.
Understanding amylose's helical configuration gives insight into how structure affects function in biological molecules.

Cellulose Structure

Cellulose is another remarkable molecule, renowned for its role in the plant cell walls. It too is made up of glucose units, but in cellulose, these units are connected via \( \beta(1 \longrightarrow 4) \) glycosidic bonds. This type of linkage is significantly different from the alpha linkages found in amylose.
Because of these \( \beta \) linkages, cellulose has a very straight, linear chain structure. These chains are capable of forming strong and rigid microfibrils with excellent tensile strength. This structural arrangement is why cellulose can serve as a critical structural component in plants, aiding in maintaining shape and rigidity.
Furthermore, the linear and extended chains of cellulose create a network that isn't easily broken down. This makes cellulose somewhat indigestible for humans, but it acts as great dietary fiber, aiding in the digestion process by promoting healthy bowel movements.

Alpha and Beta Linkages

The differences between \( \alpha \) and \( \beta \) glycosidic linkages are subtle yet substantially influential in a polymer's properties. An \( \alpha \) linkage occurs when the -OH group on the first carbon of a glucose unit is below the plane of the ring, resulting in a bond that causes the polymer to coil. This is seen in amylose with its \( \alpha(1 \longrightarrow 4) \) linkages. The helical shape is essential for the compact storage form of glucose in starch.
In contrast, a \( \beta \) linkage is formed when the -OH group is above the plane of the ring. This inversion results in a mighty straight chain, as observed in cellulose with the \( \beta(1 \longrightarrow 4) \) linkages. This structure contributes to the rigidity and tensile strength of the cellulose, making it ideal for structure and support.
Recognizing these linkages is fundamental in biochemistry as it affects how these substances interact with other biological systems. Emphasizing on these linkages helps predict and understand the function and applications of these biopolymers in both biological systems and industry.