Question

What is the difference between a monosaccharide, a disaccharide, and a polysaccharide? Give one example of each.

Short answer

A monosaccharide is a single sugar molecule (e.g., glucose), a disaccharide consists of two sugar molecules bonded together (e.g., sucrose), and a polysaccharide is a long chain of sugar molecules (e.g., starch).

Step-by-step solution

Identify Monosaccharides

A monosaccharide is the simplest form of carbohydrates. It cannot be hydrolyzed into simpler sugars. Examples include glucose, fructose, and galactose.

Identify Disaccharides

A disaccharide is made up of two monosaccharide molecules bonded together. Common disaccharides include sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar).

Identify Polysaccharides

Polysaccharides consist of long chains of monosaccharides linked together. They can be used for storage of energy or as structural components. Examples are starch and cellulose in plants, and glycogen in animals.

Key concepts

Monosaccharides

Monosaccharides are the building blocks of carbohydrates, composed of single sugar molecules. They are the simplest form of carbohydrates and represent the most basic units of carbohydrates, often referred to as simple sugars. Each monosaccharide has its unique structure and function.

Due to their simple structure, monosaccharides are quickly absorbed by the body, providing immediate energy. This is why eating foods high in simple sugars can cause a rapid spike in blood sugar levels. Some familiar monosaccharides are glucose, fructose, and galactose. Glucose is a primary source of energy for the body's cells, fructose is found in fruits and honey, and galactose is a component of milk sugar.

Disaccharides

Disaccharides consist of two monosaccharide molecules linked by a glycosidic bond. They are often called double sugars or reducing sugars due to their ability to act as a reducing agent in chemical reactions.

During digestion, disaccharides are broken down into their monosaccharide components by enzymes. This provides a slower and more sustained release of energy compared to monosaccharides. Sucrose (table sugar), which is glucose plus fructose, lactose (milk sugar), made of glucose and galactose, and maltose (malt sugar), formed from two units of glucose, are the most common examples of disaccharides.

Polysaccharides

Polysaccharides are complex carbohydrates formed by the linkage of many monosaccharide units. Due to their complexity, they are digested more slowly than monosaccharides or disaccharides, providing a more prolonged and stable energy release.

Energy Storage and Structural Functions

Depending on their function and structure, polysaccharides are classified into two main types: those that are used primarily for energy storage, like starch in plants and glycogen in animals, and those that provide structural support, such as cellulose in plant cell walls and chitin in the exoskeletons of insects and crustaceans.

Polysaccharides do not taste sweet and are not soluble in water, making them different from simple sugars, both in taste and in their physical properties.

Carbohydrate Examples

Carbohydrates come in various forms and are found in many types of food.

Monosaccharide Examples

Glucose can be found in fruits, honey, and sports drinks; fructose in fruits, root vegetables, and honey; and galactose is part of the lactose found in milk.

Disaccharide Examples

Sucrose is common in sugar cane, sugar beets, and as table sugar; lactose is found in milk and dairy products; and maltose appears when grains are fermented, as in the production of beer and malt liquors.

Polysaccharide Examples

Starch is present in foods like potatoes, bread, and rice; cellulose forms the fibrous part of vegetables, legumes, and whole grains; and glycogen is stored within the muscles and liver of animals. Understanding these examples aids in recognizing carbohydrate sources in your diet and how they are used by the body for various functions.