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The Nature of Lipids Fats & oils are formed from molecules of glycerol Lipids are a diverse collection of substances that have a range of different functions in living systems Lipids are compounds that serve both as structural and nutrient substances The lipid group includes fats and oils, waxes, steroids and phospholipids. These molecules have a low solubility in water but a high solubility in solvents such as ethanol and chloroform Fats & oils are formed from molecules of glycerol and fatty acids

A Fatty Acid Glycerol The Components of Fats & Oils Carboxylic Glycerol is a 3-carbon alcohol molecule Fatty acids are composed of hydrocarbon chains of varying length with a methyl group at one end and a carboxylic acid group at the other A Fatty Acid Carboxylic acid group Hydrocarbon chain Methyl group Glycerol

Unsaturated fatty acid: Saturated & Unsaturated Fatty Acids 3 2 Saturated fatty acid General formula for a saturated fatty acid 2 n 3 Double bond Unsaturated fatty acid: less saturated with hydrogen atoms

Saturated & Unsaturated Fatty Acids All the linkages between the carbon atoms in the hydrocarbon chain are single bonds: these fatty acids are therefore saturated with hydrogen atoms Saturated fats consist entirely of saturated fatty acids and are the animal fats Saturated fats are solid at room temperature

at which the lipid melts Saturated & Unsaturated Fatty Acids Unsaturated fats contain unsaturated fatty acids and thus possess a number of double bonds In general, the greater the number of double bonds, the lower the temperature at which the lipid melts The large number of double bonds in vegetable oils accounts for their liquid state

Formation of a Triglyceride GLYCEROL THREE FATTY ACID MOLECULES -3H2O Condensation Reaction A TRIGLYCERIDE Ester bond

Phospholipids OR

Phospholipids Polar phosphate head (hydrophilic) The phosphate-containing end of the phospholipid molecule is soluble in water, while the hydrophobic fatty acid tails orientate themselves in positions away from a watery medium Polar phosphate head (hydrophilic) Hydrophobic fatty acid (lipid) tails The bipolar nature of phospholipids allows these molecules to form bilayers that form a major component of cell membranes

water Cholesterol molecules are located between the PHOSPHOLIPID tails of the phospholipid molecules where they serve to stabilise the membrane PHOSPHOLIPID BILAYER water These cholesterol molecules are also classed as LIPIDS although they belong to a very different sub-group known as STEROIDS phospholipid bilayer of cell membrane cholesterol stabilising the membrane

Summary Fats & oils are made up of carbon, hydrogen and oxygen atoms. The building blocks (monomers) of fats and oils are glycerol & fatty acid molecules. Fats & oils are TRIGLYCERIDES. Three fatty acid molecules bond to each glycerol molecule by CONDENSATION REACTIONS. The bonds formed from these condensation reactions are called ESTER BONDS. Fats & oils are chemically similar but physically different. Fats are solid at room temperature whereas oils are liquid.

Monoglycerides & diglycerides also form when glycerol and fatty acids bond by condensation reactions. Monoglycerides form when only ONE FATTY ACID bonds with a glycerol molecule. Diglycerides form when TWO FATTY ACIDS bond with a glycerol molecule. Phospholipids are DIGLYCERIDES. Phospholipids form when TWO FATTY ACIDS and a PHOSPHATE group bond to a glycerol molecule. The phosphate end of the molecule is hydrophilic (water-loving) and the two fatty acids tails are hydrophobic (water-hating). Phospholipids are a major structural component of cell membranes. Steroids such as cholesterol, oestrogen and progesterone also belong to the class lipids.

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