Organic Chemistry: Carbohydrates and Lipids - SS3 Chemistry Past Questions and Answers - page 3

Structure of Lipids:

Lipids are a diverse group of biomolecules characterised by their hydrophobic nature. They are composed of carbon, hydrogen, and oxygen atoms and have relatively low oxygen-to-carbon and hydrogen-to-oxygen ratios. The basic structural unit of most lipids is a fatty acid, which consists of a long hydrocarbon chain and a carboxylic acid group. The hydrocarbon chain can be saturated (no double bonds) or unsaturated (one or more double bonds).

Types of Lipids:

1.    Fatty Acids: Fatty acids are the building blocks of lipids and can be classified as saturated or unsaturated based on the presence of double bonds in the hydrocarbon chain.

2.    Triglycerides: Triglycerides, also known as triacylglycerols, are the most common form of lipids. They are composed of three fatty acids esterified to a glycerol molecule. Triglycerides serve as the primary storage form of energy in adipose tissue.

3.    Phospholipids: Phospholipids consist of two fatty acids esterified to a glycerol molecule and a phosphate group attached to the glycerol. The phosphate group is hydrophilic, while the fatty acid tails are hydrophobic, making phospholipids amphipathic. Phospholipids are the major components of cell membranes and form bilayers with hydrophilic heads facing outward and hydrophobic tails facing inward.

4.    Steroids: Steroids are a group of lipids with a characteristic four-ring structure. Cholesterol is a well-known steroid that plays essential roles in cell membrane structure and serves as a precursor for the synthesis of hormones like oestrogen and testosterone.

Functions of Lipids:

1.    Energy Storage: Triglycerides serve as the most efficient form of long-term energy storage in the body. They can be broken down during metabolic processes to release energy when needed.

2.    Structural Role: Phospholipids form the basis of cell membranes, providing a selectively permeable barrier between the cell and its environment. They help maintain the integrity and fluidity of cell membranes.

3.    Insulation and Protection: Adipose tissue, which consists mainly of triglycerides, acts as an insulator, providing thermal protection and shock absorption to vital organs.

4.    Hormone Synthesis: Cholesterol is a precursor for the synthesis of various hormones, including sex hormones and adrenal corticosteroids.

5.    Vitamin Transport: Some lipids function as carriers for fat-soluble vitamins (A, D, E, and K) in the bloodstream, facilitating their absorption and utilisation in the body.

6.    Cell Signalling: Lipids, particularly phospholipids, play a role in intracellular signalling pathways, affecting cell behaviour and response to external stimuli.

In conclusion, lipids are essential biomolecules with diverse functions in living organisms. They serve as a crucial source of energy, form the structural basis of cell membranes, act as hormone precursors, and play various other roles in cell signalling and vitamin transport. The unique properties of lipids, particularly their hydrophobic nature, make them indispensable for life processes in both animals and plants.