Question

What is the empirical formula of glycogen? What is the unit that forms the basis of the glycogen polymer? What form of linkage joins these monomeric units?

Short answer

The empirical formula of glycogen is \(C_6H_10O_5\), and the monomeric unit forming the basis of the glycogen polymer is glucose. These glucose units are joined by α(1→4) and α(1→6) glycosidic linkages, with linear chains linked through α(1→4) glycosidic bonds and branches occurring at α(1→6) glycosidic linkages.

Step-by-step solution

Determine the empirical formula of glycogen

Glycogen is a polysaccharide and an energy storage molecule in animals and fungi. The empirical formula of a molecule is the simplest whole number ratio of the atoms present in the compound. In the case of glycogen, it is composed of glucose molecules, and its empirical formula is the same as that of glucose, which is C_6H_10O_5.

Identify the unit that forms the basis of the glycogen polymer

The unit that forms the basis of the glycogen polymer is the monosaccharide glucose. Glycogen is a large, branched molecule containing many glucose residues. Glucose units are connected through glycosidic linkages, which will be discussed further in step 3.

Identify the form of linkage that joins the monomeric units

The glucose units in glycogen are connected through two types of glycosidic linkages: α(1→4) and α(1→6). The linear chains of glucose residues are linked through α(1→4) glycosidic linkages, while branches occur at α(1→6) glycosidic linkages approximately every 8-12 glucose units. Both linkage types involve the glucose molecule's anomeric carbon (C-1) and the hydroxyl group at position C-4 or C-6 of the adjacent glucose unit. In summary, the empirical formula of glycogen is C_6H_10O_5, the monomeric unit is glucose, and the linkages joining these units are α(1→4) and α(1→6) glycosidic linkages.

Key concepts

Empirical Formula of Glycogen

The empirical formula of a compound represents the simplest ratio of atoms in its molecules. For glycogen, this ratio is the same as that of its monomer unit, glucose. Glucose has the chemical formula \( C_6H_{12}O_6 \), but in the structure of polysaccharides like glycogen, water molecules are released during the formation of each linkage.
As a result, the empirical formula of glycogen is often written as \( C_6H_{10}O_5 \) for the polymer chain. This shows the precise simplification of atoms that remains in the backbone of glycogen after it becomes a polymer through dehydration.
Understanding the empirical formula helps in identifying the composition of glycogen in terms of carbon, hydrogen, and oxygen, thus making it easier to study its chemical properties in biological contexts.

Monosaccharide Glucose as the Building Block

Glycogen is made up of many smaller molecules called monomers. The primary monomer in glycogen is the simple sugar, glucose. This particular form of carbohydrate is essential for energy in cells. When glucose combines, it forms glycogen, which is stored in the liver and muscles for energy during later use.
Glucose itself is classified as a monosaccharide, the simplest form of sugars. It comprises six carbon atoms, twelve hydrogen atoms, and six oxygen atoms, arranged uniquely to provide its characteristics. The repetition of glucose units in long chains creates the complex structure of glycogen, allowing it to serve as an energy reserve.

Glycosidic Linkages in Glycogen

The structure of glycogen is held together by specific types of bonds known as glycosidic linkages. These linkages form as a result of a dehydration reaction between individual glucose molecules.
In glycogen, the primary type of linkage is the\( \alpha(1\rightarrow4) \) glycosidic linkage, which connects glucose units in a linear sequence. About every 8-12 glucose units, a branching point occurs where \( \alpha(1\rightarrow6) \) glycosidic linkages form, giving glycogen its branched structure.
This branching significantly enhances the solubility and accessibility of the stored glucose, making glycogen a highly efficient energy storage molecule. The linkage types are crucial for understanding how glycogen stores and releases energy in biological systems.