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). Amylose has \( \alpha(1 \rightarrow 4) \) linkage and cellulose has \( \beta(1 \rightarrow 4) \) linkage.

Step 1: Understanding the Structure of Amylose

Amylose is a component of starch and is a linear polymer of glucose. In its structure, glucose units are linked together by \( \alpha(1 \rightarrow 4) \) glycosidic bonds. This means that the first carbon of one glucose molecule is connected to the fourth carbon of the adjacent one through an alpha linkage.

Step 2: Understanding the Structure of Cellulose

Cellulose, on the other hand, is also a linear polymer of glucose. However, in cellulose, the glucose units are linked by \( \beta(1 \rightarrow 4) \) glycosidic bonds. This signifies that the first carbon of one glucose is linked to the fourth carbon of the next one via a beta linkage, which results in a different three-dimensional conformation as compared to amylose.

Step 3: Identifying the Correct Option

From the above descriptions, we can conclude that amylose has \( \alpha(1 \rightarrow 4) \) linkages and cellulose has \( \beta(1 \rightarrow 4) \) linkages. Thus, the correct option that describes the linkage difference between amylose and cellulose is (c).

Key Concepts

Amylose Structure

Amylose is a vital component of starch and plays a crucial role in carbohydrate storage. Structurally, amylose consists of glucose units linked together in a unbranched, linear fashion. These glucose molecules are connected by \( \alpha(1 \rightarrow 4) \) glycosidic bonds. This type of linkage is characterized by the first carbon of one glucose molecule binding to the fourth carbon of the next, creating a helical structure.

This helical conformation is due to the orientation of the \( \alpha \)-glycosidic bonds, which naturally encourages a spiral shape. Amylose's helical structure is essential as it affects the overall solubility and digestibility of starch, impacting both energy release and dietary utility in organisms. Fully understanding amylose requires a grasp of the importance of \( \alpha(1 \rightarrow 4) \) linkages and how they differ from other types of glycosidic bonds.

Cellulose Structure

Unlike amylose, cellulose is a structural polysaccharide primarily found in plant cell walls. It is essential for maintaining cell structure and rigidity. Cellulose is a linear chain of glucose molecules linked by \( \beta(1 \rightarrow 4) \) glycosidic bonds. This linkage occurs between the first carbon of one glucose and the fourth carbon of another, but differs significantly from the \( \alpha \)-linkages due to its orientation.

The \( \beta \) conformation leads to straight, rod-like structures that form layers and allow for hydrogen bonding between chains. This confers tremendous strength and rigidity, making cellulose ideal for structural support in plants.

• The straight chains allow for close packing, enhancing structural integrity.
• Hydrogen bonds between hydroxyl groups in adjacent chains add to cellulose’s strength.

Understanding cellulose and its linkage type is important for studying plant biology and the role of polysaccharides in structural applications.

Glycosidic Bonds

Glycosidic bonds are covalent interactions formed between carbohydrate molecules, essential for the structure of polysaccharides like amylose and cellulose. There are two main types of glycosidic bonds: \( \alpha \) and \( \beta \). These configurations define how glucose units connect and influence the overall structure and properties of the polymer.

1. \( \alpha(1 \rightarrow 4) \) Bonds: Found in amylose, these bonds create a helical structure vital for its storage function in starch.
2. \( \beta(1 \rightarrow 4) \) Bonds: Found in cellulose, these bonds facilitate a straight-chain formation, critical for structural applications in plant cell walls.

• \( \alpha \)-linkages enable flexibility and solubility, important for energy access.
• \( \beta \)-linkages contribute to rigidity and make breaking down cellulose challenging, affecting how organisms digest plant material.

Comprehending glycosidic bonds is crucial for understanding the diversity and functionality of carbohydrates in biological systems.