Lipids are a diverse group of compounds that contain carbon, hydrogen, and oxygen. They include fats, oils, waxes, phospholipids, and steroids. Lipids are insoluble in water due to their hydrophobic fatty acid chains but soluble in organic solvents. They form emulsions when dissolved in ethanol and added to water. Lipids serve important functions as energy stores, providing insulation and buoyancy, and forming cell membranes through phospholipids.

1. Lipids
Fats and oils

2. This is a large and diverse group
All lipids contain C, H, O
They are insoluble in water- hydrophobic
Soluble in organic solvents e.g. ethanol
Lipids are the esters formed from fatty acids
and alcohol
Joined with an ester linkage which is formed
by condensation

3. Test for lipids – the emulsion test
Lipids are soluble in ethanol
If dissolved in ethanol then added to
water a cloudy emulsion will form

4. The emulsion
test

5. TYPES OF LIPID
It is a broad group which includes -
Fats, oils and waxes
Phospholipids
Complex lipids
Steroids

6. Structure
Lipids are made of two components
Fatty acids and
Glycerol

7. FATTY ACIDS
General formula: RCOOH or
R is H or, usually, a long hydro carbon tail,
CH2
CH2
CH2
CH2
etc
This forms the “tail” in lipids
Tails are Hydrophobic because they are non-
polar

8. Fatty acid tails may be:
Saturated- these melt at higher temperatures,
or
Unsaturated- which melt at lower
temperatures, liquid at room temperature

9. They can be drawn more simply like this

10. ALCOHOL
Most lipids are esters of glycerol
They are called glycerides

11. TRIGLYCERIDES
3 fatty acids can bond with one glyceride
Each bond is formed by condensation
Ester linkages/bonds are formed

12. These are ester linkages
R = a long
hydrophobic
hydrocarbon tail

13. Lipid structure can be simplified to look
like this -

14. Triglycerides are insoluble in water (non-
polar, hydrophobic)
Soluble in organic solvents
FUNCTIONS:
Used as an energy store (fat): insoluble,
compact and high in energy due to large
number CH
Buoyancy, warmth, insulation
Release water when oxidised in respiration
NB plants store oils

15. Phospholipids
These have the same structure as
glyceraldehydes but one fatty acid replaced
by phosphate.
Phosphate group derived from phosphoric
acid.
Bonded with a phosphodiester link
The phosphate group and glycerol form a
hydrophilic head
Phospholipids used to make the lipid bilayer
in all cell membranes

16. Structure of a phospholipid

17. Or more simply: