What is the Difference Between Amylose Amylopectin and Glycogen

Carbohydrates, often called carbs, are our body’s main source of energy. There are many types of carbohydrates, and all of them are mainly composed of carbon, hydrogen, and oxygen. Amylose, amylopectin, and glycogen are three types of carbohydrates.

What is the difference between amylose amylopectin and glycogen? Amylose is a straight, unbranched chain of glucose units, while amylopectin is a highly branched chain of glucose units, and glycogen is similar to amylopectin but with more branches.

Key Areas Covered

1. What is Amylose  
      – Definition, Features, Structure 
2. What is Amylopectin 
      – Definition, Features, Structure 
3. What is Glycogen
      – Definition, Features, Structure
4. Similarities Between Amylose Amylopectin and Glycogen
      – Outline of Common Features
5. Difference Between Amylose Amylopectin and Glycogen
      – Comparison of Key Differences
6. FAQ: Amylose Amylopectin and Glycogen
      – Answers to Frequently Asked Questions

Key Terms

Amylose, Amylopectin, Glycogen, Carbohydrates, Starch

What is Amylose

Amylose is a type of starch (carbohydrate). Chemically, it is a polysaccharide made up of a large number of units of sugar. There may be 100-1000 glucose units in amylose.  Amylose is made from such glucose monomer units bound with each other using glycosidic bonds. In amylose, the specific type is an α (1→4) glycosidic bond. This means the carbon atom number 1 (C1) on one glucose molecule links to the carbon atom number 4. Due to its straight structure, amylose can coil up into a helical shape, making it less tightly packed than amylopectin. This helical shape is due to the α(1→4) linkages. This tightly packed helical nature prevents the interaction of water with hydroxyl groups. Hence, amylose is less soluble in water than amylopectin. This helical structure also makes amylose resistant to easy digestion by enzymes like amylase.

Figure 1: Amylose Structure

In plants, amylose acts as an energy-storing unit. The helical structure allows plants to pack more energy into a smaller space. This packing makes amylose useful in long-term energy storage.

Amylose has a unique interaction with iodine. The helical structure traps iodine molecules within its coils, forming a characteristic blue-black complex. This reaction is useful in scientific tests to identify starch and differentiate between amylose and amylopectin.

What is Amylopectin

Amylopectin is another main component of starch. Unlike the linear structure of amylose, amylopectin is a highly branched molecule. Amylose is also built from glucose monomer units combined with each other. The type of bond used to connect these glucose monomer units is the alpha glycosidic bond. There are two types of alpha glycosidic bonds in amylopectin. They are:

α(1→4) linkages: These are the same as in amylose and connect glucose units in a linear manner.
α(1→6) linkages: These branching points connect a glucose unit to the C6 position of another glucose unit, creating side chains that branch off the main chain.

Figure 2: Amylopectin Structure

Short linear chains of α(1→4) linked glucose units (around 20-25 units) are connected by α(1→6) linkages. Amylopectin is densely packed due to the extensive flexibility of branching found in the molecule. Hence, the molecule is capable of storing energy efficiently.

The extensive branching allows for more hydroxyl groups (OH) to interact with water molecules, making amylopectin more water-soluble compared to amylose. Moreover, due to its branched structure, amylopectin is more readily broken down by enzymes like amylase, leading to a higher glycemic index compared to amylose releasing energy more quickly.

What is Glycogen

Glycogen is a complex carbohydrate made up of glucose monomer units. Glycogen utilizes two types of α-glycosidic bonds:

α(1→4) linkages: These form the backbone of the molecule, connecting glucose units in a linear chain.
α(1→6) linkages: These branching points create a highly branched structure vital for glycogen’s function.

Glycogen has a highly branched structure due to the presence of α(1→6) linkages. It packs tightly within cells due to the flexibility of the branches. This allows for efficient storage of energy within the liver and muscle.

Figure 3: α(1→4) Linkages in Glycogen

Compared to amylopectin, glycogen has shorter linear chains (around 8-12 glucose units) between branching points. This allows for quicker access to glucose units for energy needs. Moreover, just like amylopectin, glycogen’s structure limits its solubility in water.

Similarities Between Amylose Amylopectin and Glycogen

1. All three are polysaccharides.
2. The glucose units in each are linked by the same type of chemical bond: alpha (α) glycosidic bonds.
3. All three serve as a form of energy storage.
4. Enzymes can break down all three compounds.

Difference Between Amylose Amylopectin and Glycogen

Definition

• Amylose is a linear polysaccharide found in starch, which is responsible for its firm structure, while amylopectin is a highly branched polysaccharide found in starch, making it easier to break down and quickly release glucose for energy. Glycogen, on the other hand, is a branched polysaccharide stored in the liver and muscles of animals, used as a rapid-release energy source during high energy demand.

Structure

• Amylose has a straight, unbranched chain with glucose units linked by only α-1,4 glycosidic bonds. Amylopectin has a highly branched structure. Its main chain consists of α-1,4 glycosidic bonds, but there are also branches created by α-1,6 glycosidic bonds at irregular intervals. Meanwhile, glycogen is a branched structure with α-1,4 glycosidic bonds as the main chain and α-1,6 glycosidic bonds creating even more branches than amylopectin.

Found in

• Amylose and amylopectin are found in plant cells, particularly seeds, tubers, and fruits, as the main component of starch for energy storage. Glycogen, on the other hand, is stored mainly in muscle and liver cells in animals for quick energy access.

Component in Starch

• Amylose is a minor component of starch (20-30%), while amylopectin is a major component of starch (70-80%). Glycogen is prsent in animals, primarily in muscles and liver.

Water Solubility

• Amylose is more water-soluble due to its linear structure, whereas amylopectin and glycogen are less water-soluble due to their branched structure.

Conclusion

Amylose, amylopectin and glycogen are three types of carbohydrates. The basic difference between amylose amylopectin and glycogen is their structure. Amylose is a straight, unbranched chain of glucose units, while amylopectin is a highly branched chain of glucose units, and glycogen is similar to amylopectin but with more branches. This change in structure leads to changes in different properties of these compounds such as solubility.

FAQ: Amylose Amylopectin and Glycogen

1. Why is amylopectin more soluble than glycogen?

Amylopectin is more water soluble than glycogen due to its branched structure. These branches prevent tight packing, allowing more water molecules to interact and dissolve it better than the slightly less branched glycogen.

2. What is the major difference between amylose and amylopectin?

Amylose and amylopectin differ in their structures. Amylose is a straight chain of glucose units, while amylopectin has branches. This branching makes amylopectin more soluble and easier to digest than the straighter, more compact amylose.

3. Which is digested more quickly, amylose or amylopectin?

Amylopectin’s branches offer more accessible points for digestive enzymes to attack, while amylose’s straight structure takes longer to break down.

4. What is the function of amylopectin?

Amylopectin stores energy in plants by holding glucose in a way that enzymes can quickly release it when the plant needs energy for growth or other activities. This helps plants survive when sunlight or other conditions are limited.

5. What is the function of glycogen?

Glycogen, made of glucose, acts as the body’s main energy reserve. It’s stored in the liver and muscles, and is ready to be quickly turned into energy when needed, like during exercise or when blood sugar levels drop.

Reference:

1. “Amylose – – An Overview.” Science Direct.
2. “Amylopectin – An Overview.” Science Direct.
3. “What is Glycogen?” WebMD.

Image Courtesy:

1. “Structure of Amylopectin” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Amylose2” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
3. “Glycogen2” By ArthurCammers – Own work (CC BY-SA 4.0) via Commons Wikimedia