Lipids contain the elements
Carbon
Hydrogen
Oxygen
There are two main groups:
Triglycerides
Phospholipids
Triglycerides
one glycerol molecule
3 fatty acids
fatty acid
glycerol
Glycerol
C3H8O3
H
H
C
OH
H
C
OH
H
C
OH
H
Fatty Acids
carboxylic acid group (COOH)
joined to a long tail of
carbon and hydrogen atoms
The length of the hydrocarbon tail varies,
giving rise to the various fatty acids.
R, giving the
R.COOH
The tail is normally written as
formula
Fatty acids
• Organic acids with a carboxyl
(-COOH) group at the end
• Joined to the carboxyl group is a long
hydrocarbon tail
• This tail differs in each fatty acid
• The properties of a lipid depend on
the fatty acids they contain
• Fatty acids vary in 2 ways –
• the length of the HC chain
• how saturated the molecule is.
Fatty Acid
R
H
R.COOH
COOH
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
O
C
OH
Saturated Fatty
Acids
•All bonds between carbon
atoms are single
•high melting points
•solids at room temperature
•associated with animal fats
Unsaturated
Fatty Acids
•One or more double bonds
between carbon atoms
•low melting points
•liquid at room temperature
•associated with plant oils
Formation of a triglyceride
• Formed as a result of 3 condensation
reactions between glycerol and 3 fatty
acids
• involving the –OH group of glycerol
and the –COOH group of the fatty acid
• These reactions result in the formation
of 3 molecules of water.
• The bond between glycerol and the
fatty acid is called an ester bond.
Formation of a triglyceride
condensation
H
H
OH HOOC.R
O
OC.R
R.COOH
OHH2O
C
ester bond
H
C
OH HOOC.R
O
OC.R
R.COOH
OHH2O
H
C
OH HOOC.R
O
OC.R
R.COOH
OHH2O
H
glycerol
triglyceride
fatty acids
3 water
Phospholipids
Composed of glycerol, 2 fatty
acids and a phosphate
group.
Draw and label diagram p17
Hydrophilic (water loving) head
contains glycerol and phosphate group
Hydrophobic (water hating) tail
contains 2 fatty acids
• The glycerol and phosphate part is
polar and dissolves in water
(hydrophilic)
• The fatty acids are non-polar and
insoluble (hydrophobic)
• If placed in water the phosphate
heads dip into the water and the
tails stick out, forming a monolayer
• Draw diagram page 17
AIR
Hydrophobic tails
WATER
Hydrophilic heads
When shaken in water phospholipids form hollow balls
called micelles; the hydrophilic head on the outside
and the hydrophobic tails pointing inside.
Phospholipids are important
in cell membranes where
they form a phospholipid
bilayer; a double layer, heads
out, tails in.
Hydrophilic heads
Phospholipid
bilayer
Hydrophobic tails
Hydrophilic heads
Functions of lipids
•
•
•
•
Cell membrane
Energy store
Insulation
Waterproofing/repellent/wax
covering on plant
cuticle/exoskeletons
• Buoyancy
• Protection
• Storage of fat soluble vitamins