Intermediate Topic 829 of 1102 Organic Chemistry
Lipids
Fats, oils and related molecules insoluble in water, serving as energy stores and membranes.
In-depth explanation of Lipids
Lipids are a broad family of biological molecules that are largely hydrophobic and insoluble in water, including fats, oils, waxes, phospholipids and steroids. Triglycerides are esters of glycerol with three fatty acids, and they are the main energy stores in animals and plants, releasing about 38 kJ per gram on oxidation, more than twice the energy of carbohydrates. Phospholipids have a polar head and two hydrophobic tails, so they assemble spontaneously into bilayers that form the membranes of cells. Unsaturated fatty acids have kinks that keep fats liquid at room temperature.
Going deeper: Lipids
Key ideas: Lipids are biomolecules that dissolve in nonpolar solvents: triglycerides (esters of glycerol with three fatty acids), phospholipids, waxes, steroids and terpenes. Saturated fatty acids pack tightly and give solid fats, while cis unsaturated ones kink and give liquid oils. Phospholipids have a hydrophilic head and two hydrophobic tails forming bilayers. Iodine number measures unsaturation and saponification number chain length.
Common mistakes and connections: Students call all lipids fats or triglycerides, forgetting steroids and waxes. Another error is thinking trans fats are like cis; hydrogenation creates trans isomers which pack like saturated fats. Links to esters, saponification, membranes and steroids.
Visualization of Lipids
Each cis double bond kinks the fatty acid chain and lowers its melting point, so unsaturated fats are liquid oils. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Olive oil is rich in oleic acid, a monounsaturated fatty acid with one cis double bond.
Frequently asked questions about Lipids
What is Lipids?
Fats, oils and related molecules insoluble in water, serving as energy stores and membranes.
Is Lipids a beginner, intermediate or advanced topic?
Lipids is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Lipids?
Study these earlier topics in Organic Chemistry first: Amino Acids, Zwitterions, Peptide Bond.
What comes after Lipids?
The next topics in Organic Chemistry are Nucleic Acid Structure and Polymers Overview.
Can I practise Lipids with quizzes?
Yes. The interactive lesson includes a self-check question on Lipids, and the Organic Chemistry quiz draws on every topic in this area.
Where Lipids fits in Organic Chemistry
Lipids is topic 101 of 148 in Organic Chemistry.