3.2 Lipids

Lipids: a large and varied group of organic compounds.

Lipids include:

Triglycerides

Phospholipids

Waxes

Cholesterol and Steroids

Lipids are all non-polar and do not dissolve in water

Triglycerides are one of the most common types of lipids

Triglycerides consist of one molecule of glycerol bonded to three fatty acid molecules

Each fatty acid is linked to the glycerol molecule by an ester bond

C C C

H

OH

H

H H

H

OH OH

Glycerol

Hydroxyl groups

Fatty Acids:

General Formula: CH3 (CH2)n C

O

OH

Carboxyl group

H C C C

H

H

H H

H H

C C C

H

H

H H

H H

C

O

OH

CH3 CH2

H C C C

H

H

H H

H H

C C C

H

H

H H

H H

C

O

OH

Can be drawn as:

C

O

OH

Forming a monoglyceride:

C

C

C

H OH

H

H

H

H

OH

OH

C

O

OH

C

C

C

H OH

H

H

H

H

OH

O C

O

+ H2O

Ester bond

Hydroxyl group and carboxyl group react

This is a condensation reaction

C

C

C

H O

H

H

H

H

O

O C

O

C

O

C

O

A triglyceride:

Can be drawn as:G

lyce

rol

Fatty acid

Fatty acid

Fatty acid

Ester bond

To split these ester bonds and separate a fatty acid from glycerol we need to add a molecule of water

C

C

C

H OH

H

H

H

H

OH

O C

O

+ H2O

C

C

C

H OH

H

H

H

H

OH

OH

C

O

OH

This is a hydrolysis reaction

Uses of Lipids in Living Things

1. Long-term energy stores

Human Adipose Tissue Plant Oils

2. Buoyancy for marine animals: lipids are less dense than water so help animals float

3. Insulation: a layer of fat beneath the skin cuts down heat loss

4. Production of water: fatty acids produce a lot of metabolic water when they are oxidised during respiration

e.g. C17H35COOH + 26 O2 18 CO2 + 18 H2O (a typical fatty acid)

Camels’ humps are made of fat

Homework:

Compare the relative advantages and disadvantages to an organism of using carbohydrates and lipids as energy stores

To be handed in on a separate sheet of paper.