Lipids

AS Biology

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What are Lipids?

Lipids are organic molecules found in every type of cell

They are insoluble in water but soluble in organic solvents e.g. ethanol. 

The most common lipids (that we eat) are triglycerides, they are used as energy stores in plants and animals

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Structure of a Lipid

A condensation reaction removes water from between the glycerol and fatty acids to form ester bonds.


Three ester bonds in a triglyceride formed from glycerol and three fatty acids (3H20 are removed)

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Saturated Fats

If the fatty acids in a chain have the maximum number of hydrogen atoms then they are saturated
The saturated fatty acid chain is long, straight and packed together closely.


There are no C=C bonds and no more hydrogens can be added to the saturated fatty acid.
Animal fats from meat and dairy are sources of saturated fats.

They have strong intermolecular bonds which means that they are solid at room temperature 

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Unsaturated Fats

Monounsaturated fats have one double bond between two carbon atoms

Polyunsaturated fats have a larger number of double bonds between carbon atoms

A double bond causes a kink in the hydrocarbon chain, the kinks stop the chains packing together closely. 

The intermolecular bonds between unsaturated triglycerides are weak which means that unsaturated fats are liquid at room temperature e.g. vegetable oils

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