Lipids

1. Lipids
Learning objectives…
•Show the formation of a triglyceride
•Compare the structure of phospholipids and
triglycerides
•Relate structure to function

2. Type of lipids…
• Triglycerides
• Phospholipids

4. Glycerol + 3 fatty acids  triglyceride+ water
CONDENSATION

5. Triglyceride + water glycerol + 3 fatty acids
HYDROLYSIS

6. Glycerol and Fatty Acids
• Found in all storage fats and oils, including
membranes
• The glycerol molecule is always the same, but the
fatty acid differs
• Most fatty acids can be made, except for ones
called essential fatty acids which must be eaten

7. Fatty Acids
• All fatty acids have an acid group (part) at one
end, the rest of the molecule is a hydrocarbon
chain (a chain made of carbons and
hydrogens)
• The hydrocarbon chain can be 2 to 20 carbons
long, but most have around 18
Acid Group Hydrocarbon chain

9. Phospholipids
• Almost the same as a triglyceride, but the third fatty acid is
not added, instead a phosphate joins to the 3rd OH by a
condensation reaction
• The phosphate head is hydrophilic, and the fatty acids are
hydrophobic.
• As the majority of the molecule is insoluble, but the
phosphate head is hydrophilic it is able to form membranes

10. Phospholipids in membranes
• Phospholipids may still be
saturated or unsaturated.
• Organisms can control the
fluidity of their membranes
using this feature
• Organisms living in colder
climates have more
unsaturated fatty acids in
their phospholipid
molecules ensuring their
membranes remain fluid in
low temperatures

12. Notes…
• Relate the structure and function of
triglycerides and phospholipids
• Page 16-18

13. (p) compare, with the aid of diagrams, the structure
of a triglyceride and a phospholipid;
Triglyceride
Glycerol plus three fatty acids
joined by 3 ester bonds between the fatty acids
and the glycerol
In plants the fatty acids are unsaturated (many
double bonds) and the triglycerides are oils
In animals the fatty acids are saturated (few or no
double bonds) and the triglycerides are more
solid
Phospholipid
Glycerol plus two fatty acids and a phosphate
group
joined by 2 ester bonds

14. (q) explain how the structures of triglyceride and phospholipid molecules
relate to their functions
in living organisms;
Triglyceride
• Compact energy store, low mass to energy ratio (means mammals have
to carry less mass)
• Insoluble in water (large non-polar molecules)
• Does not affect cell water potential
• Stored as fat providing insulation and protection
• Provides buoyancy
• Provides waterproofing (on feathers, leaves)
• Source of water (from respiration – camel’s humps)
• Provides electrical insulation around neurones
• Helps in the absorption of fat soluble / A / D / E / K, vitamins
Phospholipid
• Part hydrophilic (head), part hydrophobic (tail), so ideal basis for cell
surface membranes
• Phosphate may have carbohydrate attached forming glycolipids
involved in cell signalling

18. Past Paper Question Mark Scheme