Triglycerides: Basics
Lipids
- Lipids are macromolecules which contain carbon, hydrogen and oxygen atoms. However, unlike carbohydrates lipids contain a lower proportion of oxygen
- They are non-polar and hydrophobic meaning they are insoluble in water
- Different types include:
- Fats and Oils (composed mainly of triglycerides)
- Phospholipids
- Steroids and waxes (considered lipids as they are hydrophobic thus insoluble in water)
Triglycerides
- These are non-polar, hydrophobic molecules
- The monomers are glycerol and fatty acids
- Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
- Fatty acids contain a methyl group at one end of a hydrocarbon chain (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group
- Fatty acids can vary in two ways:
- Length of the hydrocarbon chain
- The fatty acid may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)
- Unsaturated fatty acids can be mono or poly-unsaturated
- If H atoms are on the same side of the double bond they are cis-fatty acids and are metabolised by enzymes
- If H atoms are on opposite sides of the double bond they are trans-fatty acids and cannot form enzyme-substrate complexes, therefore, are not metabolised. They are linked with coronary heart disease
Fatty Acids Diagram
Examples of different types of fatty acids with the functional groups and presence of double bonds highlighted
- Triglycerides are formed by esterification
- An ester bond forms when the hydroxyl group of the glycerol bonds with the carboxyl group of the fatty acid
- For each ester bond formed a water molecule is released
- Therefore, for one triglyceride to form three water molecules are released
- An ester bond forms when the hydroxyl group of the glycerol bonds with the carboxyl group of the fatty acid
Triglyceride Formation Diagram
Formation of a triglyceride from a glycerol molecule and three fatty acid molecules by the process of esterification
Examiner Tip
Ensure that you are familiar with the structure of a triglyceride and that you can recognise whether the fatty acids are saturated or unsaturated.