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.

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.

Fats and oils

• Are known as triglycerides.

• Made up of one glycerol molecule joined to three fatty acids.

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

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

Fatty acids

Saturated 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

Unsaturated fatty acids• 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

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

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

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

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

Plenary - Exam questions

Plenary - Exam questions

Exam answers

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?!