Question

Digestion Disaccharides and polysaccharides cannot be broken down in the absence of water. Why do you think this is so? Include an equation in your answer.

Short answer

Disaccharides and polysaccharides cannot be broken down in the absence of water because water is essential for hydrolysis, the process responsible for breaking these complex carbohydrates into simpler monosaccharides. Water molecules are needed to break the glycosidic bonds that hold the monosaccharides together by providing hydrogen and hydroxide ions. The general equation for the hydrolysis of a disaccharide is: \( Disaccharide + H_2O \rightarrow Monosaccharide_1 + Monosaccharide_2 \) For example, the hydrolysis of lactose can be represented as: \( Lactose + H_2O \rightarrow Glucose + Galactose \)

Step-by-step solution

Understand disaccharides and polysaccharides

Disaccharides and polysaccharides belong to the carbohydrate family. Disaccharides are made up of two monosaccharide units, while polysaccharides are made up of many monosaccharide units. These complex carbohydrates serve as an essential source of energy and are broken down into simpler monosaccharides, which can be utilized by our bodies.

Describe the process of hydrolysis

Hydrolysis is a chemical process in which a compound is broken down into simpler compounds by reacting with water. In the context of carbohydrates, hydrolysis breaks down disaccharides and polysaccharides into monosaccharides. This breaking process occurs when a water molecule is added to the glycosidic bond (the bond that holds monosaccharide units together in disaccharides and polysaccharides), causing the bond to break and release the individual monosaccharides.

Explain the importance of water in hydrolysis

Water is essential for hydrolysis because it provides the necessary molecules for breaking the glycosidic bonds. During the hydrolysis reaction, a water molecule splits into a hydrogen ion (H+) and a hydroxide ion (OH-). The hydrogen ion attaches to one of the monosaccharide units, while the hydroxide ion attaches to the other monosaccharide unit, causing the glycosidic bond to break and the monosaccharides to be released.

Provide an equation for the hydrolysis of a disaccharide

Let's consider the hydrolysis of a disaccharide as an example. The general equation for the hydrolysis of a disaccharide is: Disaccharide + H2O → Monosaccharide 1 + Monosaccharide 2 A specific example would be the hydrolysis of lactose, a disaccharide composed of glucose and galactose: Lactose + H2O → Glucose + Galactose In conclusion, the absence of water prevents the hydrolysis process from occurring, as water molecules are necessary for breaking the glycosidic bonds that hold disaccharides and polysaccharides together.

Key concepts

Disaccharides and Polysaccharides

Disaccharides and polysaccharides are both types of carbohydrates that serve as vital energy sources for living organisms. Disaccharides consist of two monosaccharide units linked together. Common disaccharides include sucrose (table sugar), lactose (found in milk), and maltose (found in malted foods).

Polysaccharides are more complex, consisting of long chains of monosaccharide units. They can be straight or branched and serve various functions, from structural support in plants (cellulose) to energy storage (starch in plants and glycogen in animals). The molecular structure of these larger carbohydrates is the key to their function and the reason why water is necessary for their breakdown.

Chemical Process of Hydrolysis

The chemical process of hydrolysis is essential for digesting disaccharides and polysaccharides into forms that can be readily absorbed by living organisms. During hydrolysis, water molecules are used to cleave the chemical bonds between the monosaccharide units.

In simple terms, the water molecule, consisting of one oxygen and two hydrogen atoms, reacts with the carbohydrate molecule, inserting itself between the two monosaccharide units. This reaction causes the bond to break, leading to the formation of individual monosaccharides. The hydrolysis reaction can be facilitated by enzymes that speed up the process, making it more efficient.

Glycosidic Bond

The glycosidic bond is a covalent bond that holds together the monosaccharide units in disaccharides and polysaccharides. This bond is formed via a condensation reaction, where a water molecule is released. Depending on the nature of the bond—whether it connects two glucose molecules, for example, or a glucose and a fructose—you may have different types of glycosidic bonds, such as alpha or beta.

Breaking this bond through hydrolysis is necessary for the metabolism of carbohydrates, as it reduces complex sugars to simple, absorbable sugars. Without the disruption of the glycosidic bond, carbohydrates would remain too large to be utilized by the cells for energy.

Importance of Water in Hydrolysis

Water's role in the hydrolysis of carbohydrates is not to be understated. It serves as a reactant that facilitates the breaking of the glycosidic bond. When water is added to the equation, its molecules split into hydrogen and hydroxide ions. These ions then participate in the cleaving of the bond: the hydrogen ion bonds to one sugar molecule, while the hydroxide ion bonds to the other.

The presence of water is therefore crucial; without it, the glycosidic bonds would not be broken, and the monosaccharides would not be released. This is precisely why dehydration, or the absence of water, makes it impossible for these carbohydrates to undergo digestion and ultimately provide energy for biological processes.