Question

Carbohydrates are classified on the basis of their behaviour on hydrolysis and also as reducing or non-reducing sugar. Sucrose is a (A) Monosaccharide (B) Disaccharide (C) Reducing sugar (D) Non-reducing sugar

Short answer

Sucrose, composed of glucose and fructose units, is a disaccharide (B) and a non-reducing sugar (D), as it has no free aldehyde or ketone groups available for oxidation.

Step-by-step solution

Understand what sucrose is

Sucrose is a common sugar composed of glucose and fructose units linked together. It is widely found in nature, for example - in ripe fruits and as a primary sugar component in table sugar.

Determine whether sucrose is a monosaccharide or disaccharide

Since sucrose is composed of two sugars, glucose and fructose, linked together, it is classified as a disaccharide. So, the correct answer is not (A) Monosaccharide but (B) Disaccharide.

Understand reducing and non-reducing sugars

Reducing sugars are sugars that can be oxidized by an oxidizing agent due to the presence of a free aldehyde or ketone group. Non-reducing sugars do not have free aldehyde or ketone groups, so they cannot be oxidized.

Determine whether sucrose is a reducing or non-reducing sugar

Sucrose has no free aldehyde or ketone groups because the attachment point between glucose and fructose in sucrose involves those groups. Therefore, it is not a reducing sugar. It is classified as a non-reducing sugar. The correct answer is (D) Non-reducing sugar. So, the correct classification of sucrose based on its behavior on hydrolysis and whether it is a reducing or non-reducing sugar is (B) Disaccharide and (D) Non-reducing sugar.

Key concepts

Disaccharides

Disaccharides are a type of carbohydrate formed when two monosaccharide molecules, or simple sugars, join together in a chemical process called dehydration synthesis. This process involves the removal of a water molecule as a new bond forms between the sugars. An example that illustrates this is sucrose, which is composed of glucose and fructose.

Key characteristics of disaccharides include:

• They serve as energy sources and are often found in food we consume daily, such as table sugar and lactose in milk.
• These sugars need to be broken down into their monosaccharide components through digestion before the body can utilize them for energy or other metabolic processes.
• Common disaccharides include sucrose, lactose (composed of glucose and galactose), and maltose (composed of two glucose units).

Understanding disaccharides helps in comprehending how carbohydrates function in our diet and energy metabolism.

Reducing and Non-Reducing Sugars

Sugars are broadly categorized based on their chemical structure and behavior when they encounter certain reactive agents. A key distinction is between reducing and non-reducing sugars.

Reducing sugars are those which have a free aldehyde or ketone group that allows them to act as reducing agents. They can participate in oxidation-reduction reactions, such as the Benedict's test, a standard procedure in laboratories to test for reducing sugars.

Non-reducing sugars, on the other hand, do not have free aldehyde or ketone groups due to the way their monosaccharides are linked. Consequently, these sugars are unable to participate in redox reactions.

• Sucrose is a classic example of a non-reducing sugar. The connecting point between its glucose and fructose units involves the reactive groups, rendering it unable to act in these types of chemical reactions.
• This classification is vital for understanding the sugar's chemical properties and their behavior in biological systems.

Grasping the difference between reducing and non-reducing sugars is essential, especially for fields involving food chemistry and nutrition.

Hydrolysis of Carbohydrates

Hydrolysis is a critical biochemical reaction that involves breaking down compounds by the addition of water. For carbohydrates, hydrolysis is the process through which complex sugars, like disaccharides and polysaccharides, are decomposed into their simpler monosaccharide components.

For example, when sucrose undergoes hydrolysis, it splits into its monosaccharide components, glucose and fructose. This reaction is catalyzed by an enzyme called sucrase, present in the small intestine, aiding in digestion.

The significance of hydrolysis includes:

• It allows the body to access and use the energy stored in sugars efficiently.
• It is a crucial step in metabolism, enabling nutrients from carbohydrates to become useful for cellular respiration and energy production.

By understanding hydrolysis, we gain insights into digestive processes and how sugars function as energy sources at the cellular level.