1. © SSER Ltd.

2. 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

3. Glycerol Methyl group Carboxylic acid group A Fatty Acid Hydrocarbon chain 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

4. Double bond Unsaturated fatty acid: less saturated with hydrogen atoms 3 2 3 Saturated fatty acid General formula for a saturated fatty acid 2 n 3

5. 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

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

7. A TRIGLYCERIDE -3H 2 O Condensation Reaction Ester bond GLYCEROL THREE FATTY ACID MOLECULES

8. Monoglycerides; a single fatty acid molecule bonds with the glycerol molecule Diglycerides; two fatty acid molecules bond with the glycerol molecule

9. OR Glycerol Fatty acid Phosphate group CHCOO 2 2 Fatty acid Phosphate Polar end of the molecule (hydrophilic) – attracts water

10. OR

11. Polar phosphate head (hydrophilic) Hydrophobic fatty acid (lipid) tails 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 The bipolar nature of phospholipids allows these molecules to form bilayers that form a major component of cell membranes

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

13. CHOLESTEROL Cholesterol is one of the most common steroids and, like all other members of the group, is built around a characteristic four-ringed skeleton Apart from its role as a stabilising component of cell membranes, cholesterol is also the precursor for the synthesis of many important steroid hormones

14. TESTOSTERONE PROGESTERONE The steroid sex hormones testosterone, progesterone and oestrogen are synthesised from cholesterol

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

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