Download LIPIDS

Success Criteria
• State the composition of triglycerides
Explain the difference between a saturated
and unsaturated fatty acid
• Draw and label the structure of a
triglyceride
• Describe the formation of and label an
ester bond
Lipids contain the elements
Carbon
Hydrogen
Oxygen
They are NOT polymers as they are
not made up of monomers
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
• Organic acids with a carboxyl group
(-COOH) at the end
• Joined to the carboxyl group is a long
hydrocarbon tail (C & H atoms joined
together)
• The length of the hydrocarbon tail differs
in each fatty acid
• The tail is normally written as R, giving the
formula R.COOH
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
• 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.
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.
H2O
O
H
H
C
H
C
H
C
glycerol
H
fatty acid
O
OH
OH
ESTER BOND
OH
OH
O
H
H
H
C
C
C
C
H
H
H
H
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
Success Criteria
• State the composition of triglycerides
Explain the difference between a saturated
and unsaturated fatty acid
• Draw and label the structure of a
triglyceride
• Describe the formation of and label an
ester bond
Phospholipids
One of the fatty acids of a
triglyceride is replaced
by a phosphate group.
So they are composed of
glycerol, 2 fatty acids
and a phosphate group.
phosphate group
& glycerol
drawn as one
Glycerol residue
& phosphate group are polar
and form the hydrophilic
head of the phospholipid
2 fatty acids are non-polar
& form the hydrophobic
tail of the phospholipid.
They repel the
glycerol & phosphate
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
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