Question

Define monosaccharide, disaccharide, and polysaccharide and give an example of each.

Short answer

A monosaccharide is the simplest carbohydrate, consisting of a single sugar molecule (e.g., glucose, with the formula \(C_6H_{12}O_6\)). A disaccharide is formed by the combination of two monosaccharide molecules joined by a glycosidic linkage (e.g., sucrose, formed by glucose and fructose). A polysaccharide is formed by multiple monosaccharide molecules linked together (e.g., starch, composed of long chains of glucose molecules).

Step-by-step solution

Define Monosaccharide

A monosaccharide is the simplest form of carbohydrate, consisting of a single sugar molecule. It cannot be further broken down into simpler sugars. Monosaccharides have the general chemical formula (CH2O)n, where 'n' is a number between 3 and 7.

Provide an Example of a Monosaccharide

An example of a monosaccharide is glucose, which has the chemical formula C6H12O6. It is the most common monosaccharide and is widely used as a source of energy in cellular respiration.

Define Disaccharide

A disaccharide is a carbohydrate formed by the combination of two monosaccharide molecules, joined together by a glycosidic linkage during a dehydration synthesis reaction, where a water molecule is released.

Provide an Example of a Disaccharide

An example of a disaccharide is sucrose, which is a combination of glucose and fructose. Sucrose is commonly known as table sugar and is used as a sweetener in various food products.

Define Polysaccharide

A polysaccharide is a carbohydrate formed by the combination of multiple monosaccharide molecules, linked together by glycosidic linkages. Polysaccharides can be branched or unbranched and may have various functional roles in living organisms, such as energy storage, structural support, and cell communication.

Provide an Example of a Polysaccharide

An example of a polysaccharide is starch, which is composed of long chains of glucose molecules. Starch is a major source of stored energy in plants and is used by both plants and animals as a source of glucose for cellular respiration.

Key concepts

Monosaccharides

Monosaccharides are the simplest form of carbohydrates, often referred to as simple sugars. These molecules contain only one sugar unit, which makes them the building blocks of more complex carbohydrates. They are characterized by the presence of a single aldehyde or ketone group.
Monosaccharides generally follow the chemical formula \( \text{(CH}_2\text{O)}_n \), where 'n' typically ranges from 3 to 7. This formula indicates the ratio of carbon, hydrogen, and oxygen in these molecules.

• A common example is glucose, with the chemical formula \( C_6H_{12}O_6 \), which serves as a primary energy source in cell respiration.
• Other examples include fructose, found in fruits, and galactose, present in milk.

Disaccharides

Disaccharides are carbohydrates formed when two monosaccharide molecules are bonded together through a process known as dehydration synthesis. This means that during the formation of a disaccharide, a molecule of water is removed.
In disaccharides, the monosaccharides are connected by a covalent bond known as a glycosidic linkage. This bond is essential in holding the two sugar units together.

• Sucrose, the most well-known disaccharide (common table sugar), is composed of glucose and fructose. It is widely used as a sweetener in various food and beverage products.
• Other examples include lactose, found in milk (composed of glucose and galactose), and maltose, found in malt (composed of two glucose units).

Polysaccharides

Polysaccharides are large, complex carbohydrates formed by the linkage of multiple monosaccharide units. These can be either branched or unbranched structures, depending on how the sugar units are connected.
The function of polysaccharides can vary. Some serve as energy storage, while others provide structural support.

• Starch is an example of a storage polysaccharide, composed of numerous glucose units and is used by plants to store energy, later used by both plants and animals.
• Glycogen, similar to starch, is a storage polysaccharide but is found in animals and is stored mainly in the liver and muscles.
• Cellulose is a structural polysaccharide that forms the cell wall in plants, providing rigidity and strength.