Question

Read the given statement and select the option thatcon:d identifies \(X\) and \(Y\). In a glycogen molecule, successive glucose units are pre together by \(\mathrm{X}\) and branches are linked together by \(\mathrm{Y}\). \(X\) (a) \(1,4-\alpha\)-glycosidic bonds 1, \(4-\alpha\)-glycosidic at (b) \(1,4-\alpha\)-glycosidic bonds 1, \(6-\alpha-\) glycosidic bet 'c) \(1,6-\alpha\)-glycosidic acids 1, \(4-\alpha\)-glycosidic art d) \(1,6-\alpha\)-glycosidic acids 1, \(6-\alpha\)-glycosidic at

Short answer

The correct answer is (b) 1,4-alpha-glycosidic bonds for X and 1,6-alpha-glycosidic bonds for Y.

Step-by-step solution

Define Glycogen Structure

Understand that glycogen is a polysaccharide that serves as a form of energy storage in animals and fungi. It has a similar structure to amylopectin but is more extensively branched. Its primary structure is composed of glucose units linked together.

Identifying X - Successive Glucose Linkage

X represents the type of bond between successive glucose units in glycogen. Glucose molecules in the linear chains of glycogen are linked by alpha-1,4-glycosidic bonds.

Identifying Y - Branches Linkage

Y represents the type of bond between the branches of glycogen. The branching points in glycogen occur approximately every 8 to 10 glucose units and involve alpha-1,6-glycosidic bonds.

Analyze the Options

Match the bonds described in Steps 2 and 3 with the given options. Option (a) mentions 1,4-alpha-glycosidic bonds for both X and Y, which is incorrect. Option (b) correctly pairs 1,4-alpha-glycosidic bonds for successive glucose units and 1,6-alpha-glycosidic bonds for the branches. Option (c) and (d) incorrectly swap the bond types.

Key concepts

Alpha-1,4-Glycosidic Bonds

Understanding the intricate architecture of glycogen begins with the recognition of the alpha-1,4-glycosidic bonds. These bonds are the primary linkages that connect glucose molecules in a linear fashion, forming long chains. Imagine each glucose unit as a train car, with the alpha-1,4-glycosidic bonds being the couplings that keep the cars in line. The number 1,4 denotes the carbon atoms of each glucose unit involved in the linkage - oxygen bridges the first carbon of one unit to the fourth carbon of the next.

When discussing these bonds, the 'alpha' orientation refers to the position of the hydroxyl group (OH) attached to the first carbon; it remains below the plane of the glucose ring, which distinguishes it from the 'beta' orientation. Energy release from glycogen during metabolic processes primarily involves the breaking down of these alpha-1,4-glycosidic bonds, underscoring their critical role in energy storage and supply.

Alpha-1,6-Glycosidic Bonds

In contrast to the linear chains, glycogen's branches are created through alpha-1,6-glycosidic bonds. These bonds are less frequent but are essential for glycogen's highly branched, tree-like structure. Every 8 to 10 glucose units along the alpha-1,4-linked chains, an alpha-1,6 bond emerges, acting like a side track that deviates from the main rail line. Here, the '6' denotes the sixth carbon of a glucose unit forming the linkage, providing a new chain that can branch out and further increase the complexity of glycogen's architecture.

The presence of these alpha-1,6-glycosidic bonds is crucial for glycogen's solubility and the rapid mobilization of glucose. These branch points allow multiple enzymes to work simultaneously when glycogen is being broken down, leading to a more rapid release of glucose to meet the body's energy requirements.

Polysaccharide Energy Storage

Glycogen serves as a vital polysaccharide energy storage molecule in animals and fungi. As a polysaccharide, glycogen is made up of numerous glucose units, the simple sugars that provide energy for cellular processes. Its highly branched structure allows for the quick storage and release of glucose. When the body requires energy, enzymes break down the glycogen molecule, releasing glucose into the bloodstream.

This quick conversion from stored glycogen to available glucose is key during physical activity or between meals. Thus, the structure of glycogen - its dense branching facilitated by alpha-1,6-glycosidic bonds and its long chains held together by alpha-1,4-glycosidic bonds - plays a pivotal role in the efficiency and regulation of energy mobilization in organisms.

Glucose Units Linkage

Discussing the topic of glucose units linkage in glycogen delves into how individual glucose molecules are connected to form this complex polysaccharide. We've already highlighted the two types of glycosidic bonds responsible for its structure. However, it's the nature of these linkages that determine the physical properties and functionality of glycogen.

The linear chains (created by alpha-1,4-glycosidic bonds) and the branches (formed by alpha-1,6-glycosidic bonds) together build a molecule that is both compact and accessible. Enzymes that cleave these bonds will preferentially target the outer glucose units, which become more exposed due to the molecule's branching. The ease with which enzymes can access and break these bonds is a testament to the molecule's design, optimized for quick energy release when needed.