Question

Glycogen is a branched chain polymer of \(\alpha\)-D-glucose units in which chain is formed by C1-C4 glycosidic linkage whereas branching occurs by the formation of \(\mathrm{Cl}\)-C6 glycosidic linkage. Structure of glycogen is similar to (A) Amylose (B) Amylopectine (C) Cellulose (D) Glucose

Short answer

The structure of glycogen is most similar to amylopectin (option B), as both are branched polymers of D-glucose units with α(1→4) linkages in the main chain and α(1→6) linkages causing branching.

Step-by-step solution

1. Understand the structure of glycogen

Glycogen is a branched chain polymer of α-D-glucose units with C1-C4 glycosidic linkages forming the main chain, and C1-C6 glycosidic linkages causing the branching.

2. Structure of Amylose

Amylose is a linear polymer of D-glucose units connected through α(1→4) glycosidic linkages. As there is no branching in its structure, it is different from glycogen.

3. Structure of Amylopectin

Amylopectin is a branched polymer of D-glucose units. The main chain consists of α(1→4) glycosidic linkages, while branching occurs due to α(1→6) glycosidic linkages. This structure is similar to glycogen, as both have branched chains with α(1→4) and α(1→6) linkages.

4. Structure of Cellulose

Cellulose is a linear polymer of β-D-glucose units connected through β(1→4) glycosidic linkages. Since it does not have any branching and has β-D-glucose units, its structure is different from glycogen.

5. Structure of Glucose

Glucose is a monosaccharide and not a polymer, so its structure is fundamentally different from glycogen.

6. Compare glycogen with the options

Comparing the structures of glycogen, amylose, amylopectin, cellulose, and glucose, we can conclude that the structure of glycogen is most similar to amylopectin (option B). Both have branched chains with α(1→4) linkages in the main chain and α(1→6) linkages causing branching.

Key concepts

Glycosidic Linkages

Glycosidic linkages are the bonds formed between glucose units in polysaccharides and play a crucial role in determining their structure and function. In glycogen, which is the focus of this section, two main types of glycosidic linkages are present. These are the

• C1-C4 linkages
• C1-C6 linkages

The C1-C4 glycosidic linkages connect glucose units in a linear fashion, forming the backbone of the molecule. This type of bonding primarily involves the 1st and 4th carbon atoms of neighboring glucose units, resulting in a straight chain.

On the other hand, C1-C6 glycosidic linkages introduce branching into the structure. By linking the 1st carbon of one glucose molecule to the 6th carbon of another, this bond creates side chains every once in a while along the main chain. In the case of glycogen, this branching occurs approximately every 8 to 12 glucose units.

Both these linkages work together to form the complex, branched structure of glycogen. This structure is essential as it increases the molecule's solubility and its ability to store a large number of glucose molecules, making glycogen an efficient storage form of energy in animals.

Branched Polymers

Branched polymers are a type of polymer where the main chain grows additional branches, adding complexity to the structure. This characteristic branching is what makes them distinguishable from linear polymers. In polysaccharides such as glycogen and amylopectin, branching occurs and is an essential feature.

In glycogen, branches are formed through the C1-C6 glycosidic bond. This branching happens every 8 to 12 glucose units, resulting in a highly branched structure. Such branching allows glycogen to be compact, packing many glucose units in a small space, making it very suitable as a sugar storage molecule.

The presence of branches also facilitates the rapid addition or removal of glucose units, an important aspect for energy storage and release processes in organisms. This makes branched polymers like glycogen incredibly versatile.

Similarly, amylopectin, another branched polymer, has a structure akin to glycogen, with branches forming through C1-C6 linkages as well. Amylopectin's structure is, however, less densely branched compared to glycogen. In this manner, both these polysaccharides demonstrate the advantageous nature of branched polymers in biological systems.

Comparison of Polysaccharides

When comparing polysaccharides, it is crucial to understand their structure and function, as these define their roles in biological systems. Glycogen, amylopectin, amylose, cellulose, and glucose each have unique characteristics.

• Glycogen and amylopectin are both branched polysaccharides formed from D-glucose units. They share the presence of
  • α(1→4) linkages in their main chains
  • α(1→6) linkages for branching
  This structural similarity is why glycogen is often compared to amylopectin. However, glycogen is more densely branched, making it highly effective for quick energy release.
• Amylose, unlike its branched counterparts, is a linear polymer of D-glucose connected solely by α(1→4) linkages. This lack of branching results in a helical structure, suited to its role as a slower-releasing energy source.
• Cellulose, another essential polysaccharide, is made of β-D-glucose units linked by β(1→4) glycosidic bonds. This creates a linear, unbranched structure, forming strong fibers ideal for plant cell wall construction.
• Glucose, a simple sugar, differs fundamentally from these polymers because it is a monosaccharide. While it is the building block of more complex carbohydrates like glycogen and cellulose, it does not possess the polymeric structures seen in those molecules.

Understanding these differences helps in comprehending the diverse roles and functions these carbohydrates play in nature, from energy storage to providing structural integrity.