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Starch and Glycogen

Starch and glycogen are two types of complex carbohydrates that play crucial roles in our bodies. Starch, primarily found in plants, serves as a vital energy storage molecule for them. On the other hand, glycogen is the animal equivalent, found predominantly in our muscles and liver.

Both starch and glycogen are formed through a process called polymerization, where smaller carbohydrate units join together to form larger molecules. They are composed of glucose units linked by glycosidic bonds.

However, there are some key differences between the two. Starch samples typically have a branched structure with both amylose and amylopectin components, while glycogen has an extensively branched structure.

We will explore their formation methods, hydrogen bonding, phosphorylation processes, binding linkages, and more.

Structure and Function of Starch

Starch, a complex carbohydrate, is made up of glucose units that are joined together. It exists in two different forms: amylose, which has a linear structure, and amylopectin, which is branched. The unique structure of starch allows for efficient energy storage in plants.

Starch Composition

Starch granules consist of both amylose and amylopectin molecules. Amylose is a long chain of glucose units linked together by alpha-1,4-glycosidic bonds.

On the other hand, amylopectin contains both alpha-1,4-glycosidic bonds (like amylose) as well as alpha-1,6-glycosidic branches.

Structural Analysis

The structural information of starch can be analyzed at various levels. At the macroscopic level, starch granules have a distinct shape and size depending on the plant source.

The inner structure of starch granules consists of layers with varying degrees of crystallinity.

Efficient Energy Storage

Starch serves as an energy reserve in plants. Its branched structure increases its solubility and accessibility to enzymes during digestion or metabolism.

This allows for efficient breakdown of glucose molecules that can be used as fuel or converted into other forms such as glycogen for storage in animals.

Role in Plants

In plants, starch acts as transitory storage for excess glucose produced during photosynthesis. It accumulates within plastids called amyloplasts or chloroplasts and can be converted back into glucose when needed for growth or energy production.

Role of Starch in Energy Storage

Starch plays a crucial role in energy storage, both for plants and humans.

Let’s explore how starch functions as a storage form of energy.

Plants store excess glucose as starch for future energy needs.

Plants have the remarkable ability to convert sunlight into glucose through photosynthesis. However, they don’t always need to use this glucose immediately.

Instead, they store the excess glucose as starch for future energy requirements. Starch serves as a reservoir of energy that can be tapped into when needed.

Humans obtain starch from plant-based foods for energy.

For humans, starch is an essential source of dietary carbohydrates. We obtain starch by consuming plant-based foods such as grains (like rice and wheat), potatoes, and legumes.

These foods are rich in complex carbohydrates that our bodies break down into simpler forms during digestion.

Digestive enzymes break down starch into glucose for use by the body.

When we consume starchy foods, our digestive system breaks down the complex chains of sugars present in starch into individual glucose molecules using specialized enzymes like amylase. This process allows our bodies to absorb and utilize glucose efficiently as a source of energy.

Starch serves as an efficient way to store and transport energy within both plants and humans. It provides a readily available source of glucose when needed, ensuring that organisms have access to fuel even during periods when fresh sources of glucose may be limited or unavailable.

Digestion and Absorption of Starch

Salivary Amylase

Salivary amylase, an enzyme found in saliva, kicks off the breakdown of starch as soon as we start chewing our food. This enzyme begins the process of hydrolysis, breaking down the long chains of starch molecules into smaller fragments called maltose.

So, even before the food reaches our stomach, digestion has already begun in our mouth!

Pancreatic Amylase

Once the food enters the small intestine, pancreatic amylase takes over. This powerful enzyme continues to break down any remaining starch into maltose. It ensures that all the starch molecules are thoroughly broken apart and ready for further digestion.

Intestinal Enzymes

The next step in the process involves intestinal enzymes. These enzymes convert maltose into glucose molecules through a series of chemical reactions. Glucose is the simplest form of sugar and is easily absorbed by our body.

Absorption into the Bloodstream

After being converted into glucose, it is now time for absorption. The lining of our small intestine contains tiny finger-like projections called villi which increase its surface area for better nutrient absorption. The glucose molecules pass through these villi and enter our bloodstream.

Structure and Function of Glycogen

Glycogen, a highly branched polymer composed of glucose units, plays a crucial role in energy storage within the body. It is primarily stored in liver cells and muscle tissue, providing a readily available source of glucose when needed for energy.

The structure of glycogen consists of numerous branches connected by Glycosidic bonds. These branching structures, known as glucan chains, allow for quick and efficient release of glucose molecules.

When the body requires an immediate supply of energy, enzymes such as phosphorylase break down the Glycosidic linkages to release individual glucose units from the glycogen stores.

In liver cells, glycogen serves as a means to maintain blood sugar levels between meals or during periods of fasting. The breakdown of liver glycogen releases glucose into the bloodstream to meet the energy demands of other tissues in the body.

Muscle cells also store glycogen but utilize it primarily for their own energy needs. During strenuous exercise or physical activity, muscle cells break down glycogen to provide glucose for fueling muscular contractions.

The branching structure of glycogen allows for rapid access to stored glucose molecules when required. This characteristic distinguishes it from starch, which has a more linear structure and is predominantly found in plants.

To summarize:

  • Glycogen is a highly branched polymer made up of glucose units.

  • It is stored in liver cells and muscle tissue.

  • The branching structure enables rapid release of glucose when needed.

By understanding the structure and function of glycogen, we gain insights into its vital role as an energy reserve within our bodies.

Role of Glycogen in Energy Storage

Glycogen plays a crucial role in energy storage within our bodies. It serves as a readily available source of fuel during times when our energy needs increase, such as fasting or physical activity.

Let’s take a closer look at the specific roles liver and muscle glycogen play in maintaining our energy levels.

Liver Glycogen: Maintaining Blood Sugar Levels

During periods of fasting or intense exercise, our blood sugar levels can drop. This is where liver glycogen comes into play. The liver stores glucose in the form of glycogen through a process called glycogenesis.

When blood sugar levels decrease, the liver breaks down glycogen into glucose molecules through a process known as glycogenolysis. These glucose molecules are then released into the bloodstream to maintain stable blood sugar levels and provide energy to various organs and tissues.

Muscle Glycogen: Fuel for Muscular Contractions

Muscle glycogen takes center stage. Our muscles store glucose in the form of glycogen to use as fuel during muscular contractions. As we engage in activities like running, lifting weights, or playing sports, our muscles break down stored glycogen through the same process of glycogenolysis. T

his breakdown releases glucose molecules that are used by the muscles themselves for energy production.

In essence, both liver and muscle glycogen serve as vital sources of energy storage within our bodies. They ensure that we have enough fuel to power us through periods of fasting or intense physical exertion.

Comparison of Starch, Glycogen, and Cellulose

Starch and glycogen are both easily digestible by humans, while cellulose cannot be broken down due to its different bond arrangement.


  • Humans can efficiently digest starch and glycogen since they have the necessary enzymes to break them down into glucose molecules.

  • On the other hand, cellulose cannot be digested by humans because of its beta-linkages between glucose molecules.


  • Starch primarily serves as an energy source for plants and animals.

  • Glycogen functions as the main storage form of glucose in animals, particularly in the liver and muscles.

  • Cellulose provides structural support to plant cell walls, giving them rigidity and strength.


  • Starch is composed of two types of polysaccharides: amylose and amylopectin. Amylose consists of linear chains of glucose molecules, while amylopectin has branched structures.

  • Glycogen has even more branches than starch, allowing for a quicker release of glucose when needed for energy.

  • Cellulose is made up of long chains of glucose molecules held together by beta-linkages. This unique structure gives cellulose its strength but also makes it indigestible for humans.

Starch and Glycogen in Summary

In summary, starch, and glycogen are both polysaccharides that serve as energy-storage molecules in plants and animals, respectively. Starch is found in plants and is the primary source of carbohydrates in our diet. It consists of two forms: amylose, a linear polymer, and amylopectin, a branched polymer. Starch is broken down into glucose through digestion and provides a slow-release source of energy.

On the other hand, glycogen is the storage form of glucose in animals, including humans. It is primarily stored in the liver and muscles and acts as a readily available source of energy when needed. Glycogen has a highly branched structure which allows for quick breakdown into glucose during times of increased energy demand.

Understanding the differences between starch and glycogen can help you make informed decisions about your diet and exercise routine. Whether you’re looking to optimize your carbohydrate intake or improve your athletic performance, knowing how these molecules function can guide you toward better choices.


Can I consume starch if I have diabetes?

If you have diabetes, it’s important to monitor your carbohydrate intake closely. While starch can be part of a healthy diet for individuals with diabetes, it’s essential to choose complex carbohydrates that are digested more slowly, causing a gradual rise in blood sugar levels. Opt for whole grains like brown rice or quinoa instead of refined starches like white bread or pasta.

Is glycogen only used during physical activity?

While glycogen is primarily utilized during physical activity to provide energy for muscle contractions, it also plays an important role during periods of fasting or low blood sugar levels. When dietary sources of glucose are limited, glycogen stored in the liver gets broken down into glucose to maintain stable blood sugar levels throughout the day.

Are there any health risks associated with consuming too much starch?

Consuming excessive amounts of starchy foods can lead to weight gain and an increased risk of chronic diseases such as obesity, diabetes, and heart disease. It’s important to maintain a balanced diet by incorporating a variety of nutrient-rich foods and practicing portion control.

Can glycogen be depleted?

Yes, glycogen stores can be depleted through intense physical activity or prolonged fasting. When glycogen reserves are exhausted, the body starts breaking down stored fat for energy. This process is often seen in endurance athletes who engage in prolonged exercise sessions.

Are there any dietary sources of both starch and glycogen?

Starch is primarily found in plant-based foods such as grains (rice, wheat), tubers (potatoes), and legumes (beans). On the other hand, glycogen is not obtained directly from dietary sources but rather synthesized within the body from glucose obtained through carbohydrate consumption.

Shazzy Sheraz

I'm a passionate and experienced SEO and Technical Content Writer, dedicated to delivering high-impact content that ranks well and engages readers.