1. Lipids

2. The R group (a hydrocarbon chain)
Lipids are a group of compounds that include fats, oils and waxes. They are large molecules and all contain the elements carbon, hydrogen and oxygen.
Two main types of molecules react together when a lipid is formed: glycerol and fatty acids. Complete the diagrams below in your handbook. H H HO O C H C OH H OH H OH
The R group (a hydrocarbon chain) H
The abbreviated structural formula of a
fatty acid is:-
Glycerol, or
CH2OH
CHOH R
COOH
Which is often drawn as:- R O OH C or

3. You need to know about two types of lipids: Triglycerides and Phospholipids.
Triglycerides form when a condensation reaction joins 3 fatty acid molecules and one molecule of glycerol together. Complete the diagram below to show how the 3 fatty acid molecules would arrange themselves next to the glycerol molecule just before reacting.
After the reactions, a triglyceride molecule and 3 water molecules are formed. Complete the diagram below to show this:- C H OH C H O HO C O R C O R O
+3H2O O
3H2O
On the same diagram, use a red pen to circle the atoms that will form the 3 water molecules which will be released during the condensation reactions.
This reaction is also known as an esterification in which 3 ester bonds are formed. Highlight and label the 3 ester bonds on your triglyceride diagram above.

4. Put a label in each of the boxes.
The simplified structure of a triglyceride can be shown as a box diagram:-
A Triglyceride
Fatty Acid
Glycerol
Fatty Acid
Fatty Acid
Put a label in each of the boxes.

5. Unsaturated Fatty Acids
The properties of different fats depend on the nature of the fatty acids that are linked to it.
Make brief notes about the following:-
Saturated Fatty Acids
Present in solid fats at room temperature i.e. most animal fats e.g. lard, waxes
Have all single bonds C C in the hydrocarbon chain sections
Unsaturated Fatty Acids
Present in liquid oils at room temperature i.e. most plant oils e.g. sunflower oil, olive oil, vegetable oil.
Have one or more double bonds C C in the hydrocarbon chain sections

6. The Functions of Triglycerides
Energy Store - When respired triglycerides release 2 x as much energy as an equivalent mass of carbohydrate or protein.
Insulation from cold (e.g. fat layer in seals, blubber in whales)
Protection for Vital Organs from physical damage (e.g. layer of triglycerides round kidneys)
Buoyancy and Waterproofing (e.g. in geese and ducks)

7. A phospholipid molecule can be simplified further to:-
(b) Phospholipids are extremely important in biology because they make up the structure of all cell membranes, including the membranes found on organelles inside cells. A phospholipid molecule has a similar structure to a triglyceride, except that one fatty acid is replaced by a phosphate group. Label the phospholipid box diagram below:
A Phospholipid
A phospholipid molecule can be simplified further to:-
Phosphate Group
Fatty Acid
PO4–
(negatively charged)
Glycerol
Negatively charged phosphate group
Non-polar 2 fatty acid chains
Fatty Acid
-ve
Hydrophilic end of molecule (‘water-liking’)
Hydrophobic end of molecule (‘water-hating’)
Indicate which end of the phospholipid structure is (i) hydrophilic and (ii) hydrophobic on both of the diagrams above.

8. TASKS
Sketch to show the arrangement a collection of phospholipids makes:
(a) On water surface
(b) Immersed in water
Refs: NT p51 fig 4,
Collins Fig 8b from p12 AS
A Monolayer of
Phospholipids
A Bilayer of
Phospholipids
IMPORTANT NOTE:
The formation of phospholipid bilayers is a HUGE ADVANTAGE in cells. This is the basic arrangement of phospholipids in all membranes and it ensures that each different cell type can create it’s own particular internal environment separate to another cell, and ALSO, so that the different organelle types can create their own particular internal environment separate to other organelles.