SCH 4U
Lipids
Lipids are biological molecules that are insoluble in water but soluble in nonpolar solvents like hexane, CCl4 or benzene. Lipids are characterized by
their long hydrocarbon chains which accounts for their solubility. If a lipid
is a solid at room temperature it is referred to as a fat and if it is a liquid at
RT, an oil. The formation of a lipid is an esterification reaction. Three longchain (fatty) acids react with glycerol (propane 1,2,3 tri-ol).
CH3 – (CH2)14 – COOH
CH3 – (CH2)14 – COOH
CH3 – (CH2)14 – COOH
saturated
fatty acid
HO – CH2
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+ HO – CH
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HO – CH2
--›
glycerol (tri-ol)
CH3 – (CH2)14 – CO-O – CH2
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CH3 – (CH2)14 – CO-O – CH + 3 H2O
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CH3 – (CH2)14 – CO-O – CH2
a fat (ester)
Lipids are very important biological molecules. They store 2.25
times as much energy as either proteins or carbohydrates for the
same mass of food. In addition to storing energy, lipids provide
many vital functions:
 they are a major part of animal cell membranes
 lipids such as cholesterol or testosterone act as hormones
which regulate body functions
 vitamins A, D and E are lipids and are essential to good health
 fatty tissues in the body (lipids) act as a protective padding for
vital organs (eg. the heart). They also insulate the organ from
temperature extremes.
A fat, when reacted with a base, can create soap in a reaction
called saponification which is the hydrolysis of an ester to an
alcohol (glycerol) and carboxylic acid (sodium salt).
CH3 – (CH2)14 – CO-O – CH2
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CH3 – (CH2)14 – CO-O – CH + 3 NaOH ─>
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CH3 – (CH2)14 – CO-O – CH2
fat
CH3 – (CH2)14 – CO-O-Na+
CH3 – (CH2)14 – CO-O-Na+ soap
CH3 – (CH2)14 – CO-O-Na+
+ CH2-CH - CH2
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|
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OH OH OH
glycerol
The soap molecule is effective because the molecule has two distinct ends of
opposite polarity. The sodium salt end is water soluble and the non-polar end
is fat soluble. This allows the molecule to dissolve oils in an aqueous solution.