What is an example of a monosaccharide and a disaccharide?

January 5, 2026 •

4 min read

Did you know that all digestible carbohydrates must be broken down into their simplest forms, called monosaccharides, before the body can absorb them? To answer the question of what is an example of a monosaccharide and a disaccharide, consider the ubiquitous sugars glucose and sucrose.

Quick Summary

This article defines monosaccharides as single sugar units like glucose, and disaccharides as double sugars like sucrose, which is composed of glucose and fructose. It explains their structure, differences, and key roles in nutrition and biological processes.

Key Points

Monosaccharides are single sugars: Examples include glucose, fructose, and galactose, which are the simplest carbohydrate forms that can be directly absorbed by the body.
Disaccharides are double sugars: These are formed from two monosaccharides and must be broken down through hydrolysis before absorption.
Sucrose is a classic disaccharide example: Found in table sugar, sucrose is composed of one glucose and one fructose molecule.
Glucose is a prime monosaccharide example: Often called dextrose, glucose is the most important and abundant monosaccharide used by the body for energy.
Dehydration synthesis forms disaccharides: This chemical reaction joins two monosaccharides by removing a water molecule and creating a glycosidic bond.
Digestion breaks down disaccharides: Enzymes like sucrase, lactase, and maltase are required in the small intestine to break disaccharides back into monosaccharides for energy use.

Monosaccharides: The Simplest Sugars

Monosaccharides are the most basic and fundamental units of carbohydrates, also known as simple sugars. They cannot be hydrolyzed, or broken down, into smaller sugar molecules. Monosaccharides are crystalline, water-soluble solids and provide the most immediate source of energy for living organisms. They are the building blocks for all other, more complex carbohydrates, including disaccharides and polysaccharides.

Some of the most important monosaccharides include:

Glucose: Also known as dextrose, this is a hexose sugar (containing six carbon atoms) and is the most abundant monosaccharide. It is the most important source of energy for the body's cells, particularly the brain and nervous system. Glucose is produced by plants during photosynthesis and is stored as starch.
Fructose: Commonly known as fruit sugar, this is a ketohexose found in honey, fruits, and root vegetables. Fructose is the sweetest of all natural sugars and, like glucose, has the chemical formula C6H12O6 but a different structural arrangement.
Galactose: This monosaccharide is not typically found free in nature in large amounts. Instead, it is a component of the disaccharide lactose, or milk sugar.

Disaccharides: The Double Sugars

A disaccharide is a carbohydrate formed when two monosaccharides are joined together. This occurs through a process called dehydration synthesis, where a water molecule is removed and a covalent bond, known as a glycosidic linkage, is formed between the two sugar units. To be used by the body, disaccharides must be broken down into their component monosaccharides through hydrolysis, a reaction that consumes a water molecule.

Key disaccharides include:

Sucrose: This is common table sugar, derived from sugar cane and sugar beets. It is composed of one glucose molecule and one fructose molecule linked together.
Lactose: Known as milk sugar, this disaccharide is found in the milk of all mammals. It is formed by the combination of one glucose molecule and one galactose molecule. Lactose intolerance is caused by a deficiency of the enzyme lactase, which breaks down this bond.
Maltose: Sometimes called malt sugar, maltose is formed from two glucose molecules. It is a product of starch digestion and is used in the fermentation of beer.

Glucose and Sucrose: A Classic Example

To illustrate the difference, consider the relationship between the monosaccharide glucose and the disaccharide sucrose. Glucose is a standalone, single sugar unit that the body can use directly for energy. It is a fundamental component of cellular respiration. Sucrose, on the other hand, is a larger, more complex sugar molecule built from a glucose unit and a fructose unit. When you consume sucrose, your body must first use the enzyme sucrase to break the glycosidic bond, releasing the individual glucose and fructose monosaccharides. These individual monosaccharides are then absorbed into the bloodstream. This means that while sucrose is an important part of the diet, it is the simple sugar, glucose, that is the most essential form for energy metabolism.

The Key Differences Between Monosaccharides and Disaccharides


Feature	Monosaccharide	Disaccharide
Number of Sugar Units	One simple sugar unit.	Two monosaccharide units.
Molecular Formula	Hexoses share the formula $C6H{12}O_6$ (e.g., glucose, fructose).	Typically $C{12}H{22}O_{11}$ (e.g., sucrose, lactose).
Digestion	No digestion required for absorption.	Requires hydrolysis by enzymes to break down into monosaccharides.
Absorption	Absorbed directly into the bloodstream.	Must be broken down into monosaccharides before absorption.
Key Examples	Glucose, Fructose, Galactose.	Sucrose, Lactose, Maltose.

How the Body Uses Monosaccharides and Disaccharides

Carbohydrates serve as the primary source of energy for the body. The digestive process is a series of enzymatic reactions that break down larger carbohydrates into the smallest absorbable units. This breakdown begins in the mouth with salivary amylase for starches and continues in the small intestine, where specific enzymes like sucrase, lactase, and maltase hydrolyze disaccharides. Once broken down into monosaccharides—primarily glucose, fructose, and galactose—these sugars are transported to the liver. The liver converts fructose and galactose into glucose, which is then released into the bloodstream to be used for cellular energy or stored for later use as glycogen. The efficient processing of these sugars is vital for metabolic health.

Conclusion

In summary, the fundamental distinction between a monosaccharide and a disaccharide lies in the number of sugar units they contain. A monosaccharide, such as glucose, is a single, simple sugar molecule that is absorbed directly by the body for energy. A disaccharide, such as sucrose, is a double sugar molecule formed from two monosaccharide units and requires digestion before it can be absorbed. Understanding these basic carbohydrate building blocks is essential for comprehending how our bodies process and utilize sugars for energy and metabolic function. For further reading on the chemical structures of carbohydrates, the Chemistry LibreTexts provides an excellent resource.

Frequently Asked Questions

The main difference is the number of sugar units. A monosaccharide has one simple sugar unit (e.g., glucose), while a disaccharide has two monosaccharide units bonded together (e.g., sucrose).

A common and important example of a monosaccharide is glucose, which is a simple sugar that serves as the body's primary energy source.

Sucrose, or common table sugar, is a classic example of a disaccharide. It is formed by the bonding of one glucose molecule and one fructose molecule.

Sucrose is a disaccharide composed of one molecule of the monosaccharide glucose and one molecule of the monosaccharide fructose.

Disaccharides are formed when two monosaccharide molecules undergo a dehydration synthesis reaction, releasing a water molecule and forming a glycosidic bond.

Both monosaccharides and disaccharides serve as primary energy sources for the body. Disaccharides must first be digested and broken down into their constituent monosaccharides before they can be absorbed and used for energy.

No, while all disaccharides require hydrolysis, different enzymes are needed for each. For example, lactose requires the enzyme lactase for digestion, and sucrose needs sucrase.