Problem 67 - A Complete Resource Book in Chemistry for JEE Main

Question

The group linkage present in fats is (a) peptide linkage (b) ester linkage (c) glycosidic linkage (d) none of these

Step-by-Step Solution

Answer

The group linkage present in fats is ester linkage (b).

Step 1: Understand the context of the question

Fats, also known as triglycerides, are composed of glycerol and fatty acids. They are considered a part of the lipid family and differ from proteins and carbohydrates in their structure and the kind of bonds they form.

Step 2: Identify the type of bonds in fats

In fats, glycerol and fatty acids are linked together through a specific type of bond. This bond forms when the hydroxyl group of glycerol reacts with the carboxyl group of a fatty acid, releasing water—a process known as dehydration synthesis.

Step 3: Determine the correct linkage

The bond that is formed when a hydroxyl group and a carboxyl group react is called an 'ester linkage'. This is the bond that holds the components of fats (or triglycerides) together.

Key Concepts

Triglycerides

Triglycerides are a type of fat found in our bodies and in the food we eat. They are stored in fat cells and are an important energy source. Triglycerides are a type of lipid, which means they are hydrophobic, or water-repelling, due to their non-polar nature. They consist of:

• One glycerol molecule – a small carbohydrate relative.
• Three fatty acid chains – long hydrocarbon chains ending with carboxyl groups.

Each triglyceride molecule forms when three fatty acids bond with one glycerol molecule. This specific nature of triglycerides makes them efficient for storing energy. When our body needs energy, enzymes break down these triglycerides, releasing the fatty acids for energy use.

Lipid Structure

Lipids are a diverse group of molecules known for their role in forming biological membranes and storing energy. Unlike other macromolecules like proteins and carbohydrates, lipids do not form long polymer chains. They have unique structures that include:

• Saturated fats – no double bonds between carbon atoms, allowing maximum hydrogen atom bonding.
• Unsaturated fats – one or more double bonds create "kinks," reducing hydrogen atoms per carbon and affecting solidness at room temperature.

Triglycerides belong to lipids and have a compound structure where three fatty acids are connected to a glycerol backbone. This configuration leads to significant diversity in lipids, influenced by the length and saturation of the fatty acid chains.

Dehydration Synthesis

Dehydration synthesis is a chemical reaction whereby molecules are bonded together with the formation of a water molecule. In the context of triglycerides, dehydration synthesis is vital for forming the ester linkage between glycerol and fatty acids. Here's how it works:

• Each fatty acid loses a hydrogen atom (H) from its carboxyl group.
• The glycerol molecule loses a hydroxyl group (OH).
• These combine to form a molecule of water (H₂O), bonding the fatty acid to glycerol.

This reaction repeats for each of the three fatty acids in a triglyceride. The removal of water (hence 'dehydration') is how these molecules join, serving as an essential method of building macromolecules within the body.

Chemical Bonds in Lipids

The bonds within lipids, particularly in triglycerides, crucially determine their function and structure. Here are some key aspects of these vital lipid bonds:

• Ester Linkages: These are the main type of chemical bond in triglycerides. They occur when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids, facilitated by dehydration synthesis.
• Non-Polar Characteristics: The nature of these chemical bonds makes lipids insoluble in water, affecting how they behave and interact in biological systems.
• Bond Strength: Although ester linkages are relatively strong, they can be hydrolyzed, which means they can be broken down by adding water, a crucial step in fat metabolism.

Understanding these bonds is essential as they explain why lipids are an efficient energy storage form and how they participate in various biological processes.