Summary
Hydrophobic molecules including fats, oils, waxes and steroids used for energy storage, insulation and membranes.
In depth
Lipids are mostly nonpolar and include triglycerides, phospholipids, steroids, waxes and some vitamins. Fats give about 38 kJ per gram, roughly double the energy of carbohydrate, store little water and insulate. They are the structural basis of membranes and hormones.
Waxes waterproof leaves and skin.
Lipids are defined by solubility, not structure. Besides storage and insulation they act as signals (steroid hormones, prostaglandins), pigments (carotenoids), vitamins (A, D, E, K), buoyancy aids (blubber, oil droplets in diatoms) and waterproofing waxes. Essential fatty acids, such as linoleic and alpha-linolenic acid, cannot be made by humans and must come from the diet.
Lipids are digested with the help of bile salts, which emulsify fats into droplets so lipase has more surface to work on, then carried in blood as lipoproteins (chylomicrons, LDL, HDL).
Remember: lipids give more energy per gram partly because they are less oxidised than carbohydrates, and yield more metabolic water in respiration, which helps camels and migrating birds.
Frequently asked questions
What is Lipids?
Hydrophobic molecules including fats, oils, waxes and steroids used for energy storage, insulation and membranes.
Which area of biology covers Lipids, and how advanced is it?
Lipids is one of the 51 topics in Biomolecules & Biochemistry. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Triglycerides, Phospholipids, Polysaccharides.
Why does Lipids matter?
Fat is a compact, light energy store, which is crucial for animals that must move or migrate.
What should I learn before Lipids?
Lipids is a Beginner topic, so no earlier topic is required. Other Beginner topics in Biomolecules & Biochemistry that pair well with it include Water Properties, Carbon Chemistry, Carbohydrates.
What topics are related to Lipids?
The closest topics to Lipids are Triglycerides, Phospholipids, Polysaccharides, Steroids. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Lipids?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Lipids. To practise the whole of Biomolecules & Biochemistry, use the Biomolecules & Biochemistry quiz.
How is Lipids different from Triglycerides?
Lipids: Hydrophobic molecules including fats, oils, waxes and steroids used for energy storage, insulation and membranes. Triglycerides: Fats formed from glycerol joined to three fatty acids, the main long-term energy store in animals. Read both side by side and note what each one explains.
How should I study Lipids step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Triglycerides and explain the difference aloud. Finally, take the Biomolecules & Biochemistry quiz and come back to this page for any question you miss.