Problem 172 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

In which of the following sets do the carbohydrates contain disaccharides only? (a) Maltose, lactose, starch (b) Sucrose, lactose, cellulose (c) Maltose, sucrose, lactose (d) Maltose, lactose, mannose

Step-by-Step Solution

Answer

Option (c) Maltose, sucrose, lactose contains disaccharides only.

Step 1: Understand Disaccharides

Disaccharides are carbohydrates composed of two monosaccharide units linked together. Common examples include maltose, lactose, and sucrose.

Step 2: Analyze Each Option

Look at each set of options to determine if they all are disaccharides: - (a) Maltose, lactose, starch: Starch is a polysaccharide. - (b) Sucrose, lactose, cellulose: Cellulose is a polysaccharide. - (c) Maltose, sucrose, lactose: All are disaccharides. - (d) Maltose, lactose, mannose: Mannose is a monosaccharide.

Step 3: Select the Correct Option

Identify the set where all components are disaccharides. From the analysis, option (c) includes only disaccharides: maltose, sucrose, and lactose.

Key Concepts

Disaccharides

Disaccharides are an essential class of carbohydrates that play a significant role in biology and nutrition. They are composed of two monosaccharide units linked together by a glycosidic bond. This process occurs when a condensation reaction involves the removal of a molecule of water.
Common disaccharides include maltose, lactose, and sucrose.

• Maltose, also known as malt sugar, results from the breakdown of starch and is composed of two glucose molecules.
• Lactose, found in milk, consists of one glucose molecule and one galactose molecule.
• Sucrose, commonly known as table sugar, is composed of glucose and fructose.

They are sweet to taste and water-soluble, making them significant in food science. Unlike polysaccharides, disaccharides are easily digestible as they quickly break down into their monosaccharide components, providing an immediate energy source. The ability to quickly hydrolyze disaccharides is facilitated by enzymes such as maltase, lactase, and sucrase, each specific to its corresponding disaccharide.
Field studies often evaluate the digestive efficiency and nutritional value of these carbohydrates, primarily focusing on their impact on human energy levels and dietary habits.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and cannot be hydrolyzed into smaller carbohydrate molecules. Known as simple sugars, these consist of single carbohydrate units, making them the basic building blocks for more complex carbohydrates such as disaccharides and polysaccharides.
Some well-known monosaccharides are glucose, fructose, and galactose. Each has its own unique properties and functions:

• Glucose is the primary energy source for cells and is crucial in cellular respiration.
• Fructose is the sweetest naturally occurring sugar, commonly found in fruits.
• Galactose combines with glucose to form lactose or participates in making glycoconjugates in the body.

Monosaccharides have the general formula \( C_nH_{2n}O_n \), where the number of carbons (\( n \)) is small, typically between 3 to 7. These sugars not only provide quick energy but are also involved in more complex biosynthetic processes. Being highly water-soluble and sweet, they are fundamental in diabetes management and are key considerations in metabolic studies.
In research, monosaccharides form the backbone of studies into metabolic pathways, energy production, and even in the development of synthetic biology techniques.

Polysaccharides

Polysaccharides are complex carbohydrates composed of long chains of monosaccharide units bonded together. Unlike disaccharides and monosaccharides, these are not sweet and are typically not soluble in water.
Polysaccharides serve vital roles in both plant and animal life, providing structure and energy storage.

• Starch is the primary form of energy storage in plants; it is made up of amylose and amylopectin.
• Cellulose also comes from plants and is a major component of plant cell walls, offering structural support.
• Glycogen is the principal storage form of glucose in animals, found primarily in liver and muscle tissues.

These polysaccharides are selectively hydrolyzed by specific enzymes into simpler oligosaccharides and eventually into monosaccharides during digestion.
The study of polysaccharides extends into fields like plant biology, human nutrition, and materials science, exploring their potential in biofuel production and as biodegradable materials.