Molecules, Transport and Health
Lipids
Pearson Edexcel International A Level Biology
Triglycerides
- A triglyceride is one glycerol molecule and three fatty acid molecules.
- They join by a condensation reaction, catalysed by enzymes, and three molecules of water are formed.
- Glycerol and the fatty acids are joined by ester bonds: three in each triglyceride.
- A fatty acid is RCOOH: R is the hydrocarbon chain.
Saturated and unsaturated fatty acids
| Fatty acid | Bonds between carbons | Hydrogens |
|---|---|---|
| Saturated | Do not contain carbon-carbon double bonds | More for the same number of carbons |
| Unsaturated | Contain carbon-carbon double bonds | Fewer hydrogens for the same number of carbons |
- Both contain carbon and hydrogen and oxygen and contain covalent bonds only. Never write fatty acids both contain ester bonds.
- Unsaturated fatty acids are kinked; saturated fatty acids are straight.
- Drawing an unsaturated fatty acid: at least one carbon-carbon double bond drawn in the chain, with one H removed from each carbon of the double bond. C1 is the carboxyl carbon: never place a double bond between C1 and C2.
The C=O in every fatty acid
Every fatty acid has a C=O double bond in its carboxyl group, so a saturated fatty acid has no carbon-carbon double bonds. Never write saturated fatty acids have no double bonds.
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