Hydrolysis: The Reaction That Breaks Disaccharides into Monosaccharides

November 17, 2025 •

3 min read

According to the World Health Organization, the average person consumes a significant amount of sugar daily, much of which is in the form of disaccharides. To be used for energy, these double sugars must be broken down by a specific chemical process: a hydrolysis reaction. This fundamental biochemical process is crucial for digestion, converting larger sugar molecules into smaller, absorbable units.

Quick Summary

Hydrolysis is the chemical reaction that breaks disaccharides into monosaccharides. This process uses a water molecule to cleave the glycosidic bond connecting the two simple sugars. It is an essential part of digestion, allowing the body to absorb nutrients from carbohydrates effectively.

Key Points

Hydrolysis is the reaction: It is the chemical reaction that breaks disaccharides into monosaccharides by adding a water molecule to the glycosidic bond.
Glycosidic bonds are cleaved: The water molecule breaks the covalent glycosidic bond that links the two simple sugar units together.
Enzymes are catalysts: Specific enzymes, known as hydrolases or disaccharidases (like lactase, sucrase, and maltase), speed up these reactions in the body.
The reaction is catabolic: Hydrolysis releases energy and is the opposite of dehydration synthesis, which requires energy to form bonds.
Crucial for digestion: This process is essential for breaking down dietary sugars into molecules small enough to be absorbed by the intestines for cellular energy.

What is a Disaccharide?

Before understanding how they are broken down, it's essential to define what disaccharides are. A disaccharide is a carbohydrate formed when two monosaccharides, or simple sugars, are joined together. This bonding process, known as dehydration synthesis or condensation, removes a water molecule to form a glycosidic bond. Some of the most common dietary disaccharides include sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar). These double sugars are often too large to be directly absorbed by the body's cells and must be broken down first.

The Role of Glycosidic Bonds

At the heart of any disaccharide is the glycosidic bond, a covalent linkage that holds the two monosaccharide units together. The specific type of glycosidic bond (e.g., α-1,4 or β-1,4) determines the structure of the disaccharide and which enzymes are needed to break it down. For instance, the beta-glycosidic bond in lactose requires the enzyme lactase to be hydrolyzed, which is why a deficiency in this enzyme causes lactose intolerance.

The Hydrolysis Reaction Explained

Hydrolysis is the chemical reaction that breaks disaccharides into monosaccharides. The term itself provides a clue to its function: 'hydro' means water and 'lysis' means to break or loosen. The reaction works by inserting a water molecule across the glycosidic bond, effectively splitting the disaccharide back into its two component monosaccharides. This is the reverse of the dehydration synthesis reaction that formed the disaccharide in the first place.

Here are the basic steps of a hydrolysis reaction:

A disaccharide molecule, such as sucrose, is present.
A water molecule ($H_2O$) is added to the system.
An enzyme, such as sucrase, catalyzes the reaction, accelerating the process.
The water molecule breaks the glycosidic bond.
The disaccharide is cleaved into its two constituent monosaccharides (glucose and fructose, in the case of sucrose).

Hydrolysis vs. Dehydration Synthesis: A Comparison

To fully grasp hydrolysis, it is helpful to contrast it with its inverse reaction, dehydration synthesis. Both are critical for building and breaking down biological molecules, but they work in opposite ways.


Feature	Hydrolysis	Dehydration Synthesis
Function	Breaks down polymers into monomers.	Builds polymers from monomers.
Water Molecule	Consumed/added to break bonds.	Released/removed to form bonds.
Energy	Releases energy (catabolic).	Requires energy (anabolic).
Enzymes	Enzymes like hydrolases or disaccharidases are used.	Enzymes like synthases are used.
Result	A large molecule is split into smaller ones.	Smaller molecules are joined to form a larger one.

Examples of Disaccharide Hydrolysis

The hydrolysis of common disaccharides is a central part of human digestion and metabolism. Specific enzymes are responsible for breaking down each type of double sugar:

Sucrose Hydrolysis: Ingesting sucrose requires the enzyme sucrase to hydrolyze it into glucose and fructose. This is a key step in processing table sugar for energy.
Lactose Hydrolysis: The digestion of milk sugar (lactose) is dependent on the enzyme lactase, which splits it into glucose and galactose. Individuals with lactose intolerance lack sufficient lactase, leading to digestive issues.
Maltose Hydrolysis: Maltose is the product of starch digestion and is further broken down by the enzyme maltase into two glucose units.

The Importance of Digestion and Energy Release

In the human body, the hydrolysis of disaccharides is not just a chemical reaction; it is a vital part of digestion. The gastrointestinal tract, from the mouth to the small intestine, acts as a disassembly line for carbohydrates. Complex carbohydrates and disaccharides are sequentially broken down into monosaccharides small enough to be absorbed through the intestinal wall and into the bloodstream. Once absorbed, these monosaccharides, primarily glucose, can be used by cells as an immediate source of energy through cellular respiration. Without hydrolysis, the larger disaccharide molecules would simply pass through the digestive system undigested, and the energy stored within them would not be accessible to the body.

Conclusion

Understanding what type of reaction breaks disaccharides into monosaccharides reveals a fundamental process of biochemistry. The hydrolysis reaction, which uses water to break the glycosidic bonds within disaccharide molecules, is not only a key component of human digestion but also a cornerstone of how living organisms extract and utilize energy from carbohydrates. This catabolic process, facilitated by specific enzymes, is the essential reverse of dehydration synthesis and underpins our ability to process dietary sugars for metabolic function.

Visit Biology LibreTexts to learn more about the synthesis of biological macromolecules.

Frequently Asked Questions

Hydrolysis breaks down a larger molecule into smaller components by adding a water molecule. Dehydration synthesis, its opposite, joins smaller molecules together to form a larger one by removing a water molecule.

Hydrolysis is vital for digestion because it breaks down complex carbohydrates, including disaccharides, into simple sugars (monosaccharides) that are small enough to be absorbed from the digestive tract into the bloodstream for energy.

If the body lacks the specific enzymes needed to hydrolyze a disaccharide, it can lead to intolerance. For example, a lactase deficiency prevents the hydrolysis of lactose, causing the symptoms of lactose intolerance.

The enzyme lactase is responsible for breaking down the disaccharide lactose into its two component monosaccharides: glucose and galactose.

While hydrolysis can occur slowly without assistance, it is typically catalyzed by specific enzymes, such as sucrase or lactase, to speed up the reaction significantly, especially within biological systems.

Sucrose, which consists of glucose and fructose, is broken down by the enzyme sucrase via hydrolysis. The reaction adds a water molecule to the glycosidic bond, yielding one molecule of glucose and one molecule of fructose.

The hydrolysis of disaccharides primarily takes place in the small intestine, where specialized enzymes located on the microvilli help break down the sugars for absorption.