Lipids
லிப்பிடுகள்
Stop calling lipids macromolecules. They are not. They appear in the acid-insoluble fraction only because they form vesicles when you grind tissue. This is a classic trap in the Biomolecules chapter.
The idea
Lipids are organic compounds, generally water-insoluble. They consist of fatty acids esterified with glycerol. Fatty acids possess a carboxyl group attached to an R group, which can be a methyl, ethyl, or higher number of CH2 groups. They are classified as simple, compound, or derived lipids based on their chemical structure.
Why it matters
They provide energy storage, structural integrity to cell membranes, and act as signaling molecules.
NEET lens
NEET focuses on the 'acid-insoluble' classification trap. Memorize that lipids are not polymers. Expect questions on the structure of Palmitic acid (16 carbons) and Arachidonic acid (20 carbons). Distinguish clearly between saturated and unsaturated fatty acids based on double bonds.
Clinical significance
Dysregulation of lipid metabolism leads to atherosclerosis, where cholesterol plaques narrow the arteries. Failure to process sphingolipids results in lysosomal storage diseases like Tay-Sachs. Lipid homeostasis is critical for maintaining the structural integrity of the plasma membrane.
Introduction
Lipids are hydrophobic or amphipathic biomolecules including fats, oils, waxes, phospholipids, and steroids. They are insoluble in water but soluble in organic solvents like chloroform and ether.
Core concept
Fats/oils: triglycerides = glycerol + 3 fatty acids (ester bonds). Saturated FA = no double bonds (solid, animal fats). Unsaturated FA = one or more double bonds (liquid, plant oils). Phospholipids: glycerol + 2 FA + phosphate group → amphipathic → form bilayers (cell membranes). Steroids: fused ring structure (cholesterol, testosterone, estrogen, cortisol). Waxes: fatty acid + long-chain alcohol (cutin, suberin, beeswax).
Go deeper
Cholesterol serves triple roles: structural (membrane fluidity regulator), signaling precursor (steroid hormones, bile acids), and vitamin D precursor (when UV hits skin). Despite its 'bad' reputation, cholesterol is vital — problems arise only with excess LDL.
From Class 10
Fats provide energy and insulation. But lipids are much more than fats — they form cell membranes, hormones, and vitamins.