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The Nature of Lipids
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
The Components of Fats & Oils
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
A Fatty Acid
Carboxylic
acid group
Glycerol
Hydrocarbon
chain
Methyl
group
Saturated & Unsaturated Fatty Acids
2 3
Saturated fatty acid
2
n
3
General formula for a
saturated fatty acid
Double bond
Unsaturated fatty acid:
less saturated with
hydrogen atoms
3
Formation of a Triglyceride
THREE
FATTY ACID
MOLECULES
GLYCEROL
-3H2O Condensation Reaction
A
TRIGLYCERIDE
Ester bond
Phospholipids
Fatty acid
Glycerol
Fatty acid
Phosphate
hydrophobic
tails
hydrophilic phosphate
group
OR
Fatty acid
Glycerol
Phosphate
Fatty acid
Phospholipids
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
Polar phosphate head
(hydrophilic)
The bipolar nature of
phospholipids allows these
molecules to form bilayers that
form a major component
of cell membranes
Hydrophobic fatty acid
(lipid) tails
PHOSPHOLIPID
BILAYER
water
water
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
phospholipid
bilayer of cell
membrane
cholesterol stabilising
the membrane
Summary
 Fats & oils are made up of carbon, hydrogen and
oxygen atoms.
 The building blocks (monomers) of fats and oils are
glycerol & fatty acid molecules.
 Fats & oils are TRIGLYCERIDES.
 Three fatty acid molecules bond to each glycerol
molecule by CONDENSATION REACTIONS.
 The bonds formed from these condensation reactions
are called ESTER BONDS.
 Fats & oils are chemically similar but physically
different.
 Fats are solid at room temperature whereas oils are
liquid.
 Monoglycerides & diglycerides also form when glycerol
and fatty acids bond by condensation reactions.
 Monoglycerides form when only ONE FATTY ACID
bonds with a glycerol molecule.
 Diglycerides form when TWO FATTY ACIDS bond
with a glycerol molecule.
 Phospholipids are DIGLYCERIDES.
 Phospholipids form when TWO FATTY ACIDS and a
PHOSPHATE group bond to a glycerol molecule.
 The phosphate end of the molecule is hydrophilic
(water-loving) and the two fatty acids tails are
hydrophobic (water-hating).
 Phospholipids are a major structural component of cell
membranes.
 Steroids such as cholesterol, oestrogen and progesterone
also belong to the class lipids.