Problem 83 - A Complete Resource Book in Chemistry for JEE Main

Question

In most of the cases glycosidic linkage is formed between (a) \(\left(1 \longrightarrow 4^{\prime}\right)\) (b) \(\left(4 \longrightarrow 4^{\prime}\right)\) (c) \(\left(2 \longrightarrow 2^{\prime}\right)\) (d) \(\left(1 \longrightarrow 3^{\prime}\right)\)

Step-by-Step Solution

Answer

In most cases, glycosidic linkage is formed between 1 → 4.

Step 1: Understanding Glycosidic Linkage

Glycosidic linkage is a covalent bond that joins a carbohydrate molecule to another group, which can be another carbohydrate. This type of bond is essential in the formation of disaccharides, oligosaccharides, and polysaccharides.

Step 2: Identifying Common Glycosidic Linkages

The most common glycosidic linkage in carbohydrates, especially disaccharides, is the 1 → 4 linkage. This is often seen in structures like maltose, where one glucose molecule's C1 carbon is linked to another glucose's C4 carbon.

Step 3: Analyzing The Given Options

Analyze the given options to identify which one typically represents the most common glycosidic linkage: (a) 1 → 4, (b) 4 → 4, (c) 2 → 2, and (d) 1 → 3. From Step 2, we found that 1 → 4 is the typical linkage in common carbohydrates.

Key Concepts

Covalent Bond

A covalent bond is a strong chemical connection between two atoms that share a pair of electrons. This sharing allows each atom to achieve a stable outer electron shell, similar to what noble gases have. In the context of carbohydrates, covalent bonds are crucial as they form the backbone of many structures.
For instance, glycosidic linkages, which are a type of covalent bond, bind sugar molecules together to create complex carbohydrates.

• Glycosidic linkages connect monosaccharides (simple sugars) to form disaccharides (like sucrose and lactose) and further, complex carbohydrates.
• Covalent bonds ensure stability and strength in carbohydrate structures, making these molecules less likely to break apart in biological systems.

Understanding covalent bonds helps us appreciate how carbohydrates function in energy storage and structural support in cells.

Disaccharides

Disaccharides are carbohydrates that consist of two sugar molecules bonded together via a glycosidic linkage. These small sugar chains serve as an essential energy source in our diet.
Some common disaccharides include:

• Sucrose - made from glucose and fructose; it is found in many plants and a major component of table sugar.
• Lactose - consists of glucose and galactose; it is the sugar found in milk.
• Maltose - formed by linking two glucose molecules; it appears during the digestion of starch.

The glycosidic bonds in disaccharides can be hydrolyzed (broken down by water) during digestion, releasing simple sugars that the body can easily absorb and use for energy. This process is vital for utilizing carbohydrates as nutrients.

Carbohydrate Structure

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are classified based on the number of sugar units they contain: monosaccharides (one sugar unit), disaccharides (two sugar units), oligosaccharides (3-10 sugar units), and polysaccharides (more than ten sugar units).
The complex structure of carbohydrates is largely due to the variety of ways they can connect through glycosidic linkages.

• Monosaccharides like glucose are the simplest form and can combine to form larger structures.
• Through glycosidic bonding, these sugars link together into more complex carbohydrates, such as starch and cellulose.
• The molecular structure can vary greatly within carbohydrates due to the variety of possible linkages, allowing for a vast range of functions, from energy storage to providing structural integrity in plant cell walls.

Recognizing and understanding the structure of carbohydrates helps in grasping their biological significance and functionality in living organisms.