B1.1 Lipids
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What is the key idea of lipids?
Lipids are large, nonpolar, hydrophobic molecules used for energy storage, insulation, and membrane structure.
Why are lipids insoluble in water?
They are nonpolar and hydrophobic — no overall charge, repelled by polar water molecules.
What are the main types of lipids?
Triglycerides, phospholipids, waxes, and steroids.
What are triglycerides made of?
Glycerol + 3 fatty acids, joined by ester bonds via condensation reactions.
What is esterification?
The condensation reaction between an alcohol (glycerol) and acid (fatty acid) → ester bond + water.
What is lipolysis?
The hydrolysis of triglycerides into glycerol and free fatty acids.
Why do lipids provide more energy than carbohydrates?
Lipids are highly reduced and anhydrous, releasing >2× more energy per gram when oxidized.
How are fatty acids broken down for energy?
By β-oxidation, producing acetyl-CoA, FADH₂, NADH, which enter cellular respiration.
What is the structure of a fatty acid?
A long hydrocarbon chain with a carboxyl (-COOH) group at one end.
What is a saturated fatty acid?
Contains no C=C double bonds; fully hydrogenated; solid at room temperature (e.g., butter).
What is an unsaturated fatty acid?
Contains one or more C=C double bonds; causes kinks → liquid at room temperature (e.g., oils).
What is the difference between monounsaturated and polyunsaturated?
Mono = one double bond; Poly = two or more double bonds.
Why are unsaturated fats liquid?
Kinks prevent close packing of chains → lower melting point.
What is the biological role of phospholipids?
Form the phospholipid bilayer of cell membranes; hydrophilic heads and hydrophobic tails form a semi-permeable barrier.
What roles do waxes and oils have in organisms?
Waterproofing in plants and animals (e.g., leaf cuticle, feathers, fur).
What are steroids?
Lipids with four fused carbon rings (e.g., cholesterol, hormones).
How do lipids function in desert animals (e.g., kangaroo rats)?
Oxidation of fats produces metabolic water, sustaining them without drinking.
What other functions do lipids serve?
Thermal insulation, shock absorption, protection of organs.
Why are lipids considered an economical fuel?
They store energy in anhydrous form and yield high energy per unit mass.
What type of reaction forms ester bonds in triglycerides?
Condensation reaction, releasing H₂O.