1. Lipids Learning objectives:
describe, with the aid of diagrams, the basic structure of glycerol and fatty acids;
outline the formation of triglycerides by the condensation reactions between glycerol and fatty acids;
describe the structures of saturated and unsaturated fatty acids and outline their roles and importance in the human body;
describe, with the aid of diagrams, the structure of a phospholipid molecule.

2. About lipids
Lipids cover a large group of molecules that include fats, oils and cholesterol
Lipids are non-polar molecules. This means that they are not charged.
Lipids are hydrophobic, which makes them insoluble in water.

3. Fats and oils Are known as triglycerides.
Made up of one glycerol molecule joined to three fatty acids.

4. A fatty acid molecule is a hydrocarbon with a carboxylic acid group attached

5. Fats and oils – condensation reactions
Three fatty acids join on to one glycerol molecule by a condensation reaction.
The bonds formed are called ester bonds.
The molecule formed is a triglyceride

6. Fatty acids Saturated fatty acids Unsaturated fatty acids
Hydrocarbon chains have the maximum number of hydrogen atoms attached – it is saturated
We know this because all the bonds are single bonds
Saturated fatty acids tend to have higher melting points so are solid at room temperature
Has double bonds between carbons – does not have as many hydrogen atoms, therefore is unsaturated
Tends to be liquid at room temperature e.g. oils

7. Uses of lipids in the body
Triglycerides are the main energy source in the human body because they:
Are insoluble in water
Contain more energy per gram than carbohydrates
Are ideal for storage in adipose tissue (body fat)
Can be used for insulation around body organs and under the skin
Also protects kidneys from damage
Fat soluble vitamins A and D are stored in lipid globules inside liver cells

8. Cholesterol Is a kind of steroid but does not have the same structure
Found in the plasma membrane to keep it fluid
Other steroids are important as hormones
Testosterone
Oestrogen

9. Phospholipids
These are polar molecules that form a bilayer in cell membranes
Contain glycerol and two fatty acids and a phosphate group attached to the head region

10. Transport of lipids Lipids are not soluble in water
This means that they cannot be dissolved in blood plasma and carried around the body in the same manner as glucose
Triglycerides are broken down to glycerol and fatty acids.
Glycerol dissolves into the blood plasma
Fatty acids combine with plasma proteins and carried in the blood as small globules

11. Plenary - Exam questions

12. Plenary - Exam questions

13. Exam answers

14. How did you do? The exam questions are a self assessment tool.
If you found these questions difficult, you have not understood (or done) the pre-reading/textbook questions.
Be honest with yourself – are you working as hard as you can?!