1. Year 12 Biology Macromolecules Unit
Chapter 1: M6

2. M6: Polysaccharides & Lipids (They’re Important)
Polysaccharides are large molecules which are constructed of simple sugar units called monosaccharides linked together. Polysaccharides are always for either energy storage or structural purposes.
Lipids are things like fats, oils and waxes. They have a wide variety of purposes within the cells of an organism.

3. M6.1: Structural Importance
Structural Polysaccharides come in two varieties
Cellulose
Chitin
Cellulose is commonly the main part of plant cell walls. It is a tough, fibrous molecule that can’t be broken down or digested by most organisms, humans included.
Chitin is commonly associated with non-plant organisms. It is a molecule which bonds to itself to form a hard shell and is found in the exoskeletons of organisms like spiders, insects and crustaceans.

4. Lipids
There are different groups of lipids that serve different purposes. These groups include phospholipids, fats and oils, waxes and steroids.
All lipids are essentially similar, they are composed of fatty acid chains linked to a glycerol molecule which acts as a backbone.
The structurally significant group of lipids are phospholipids.

5. Phospholipids
The structure of phospholipids include a phosphate group which causes them to form their structure somewhat spontaneously in water.
Since cells are largely water and exist in an environment that is also largely water, this is a useful attribute for these lipids to have when they perform a vital role such as making up the cell membrane.

6. Phospholipids Cont.
Phospholipids have a hydrophilic head which likes water and a hydrophobic tail which does not.
The names come from the Greek words Phillia which means ‘love’, and Phobia which means ‘fear’.
When exposed to water the lipid will always try and point the tail away from the water. In groups this causes the lipids to clump together, tails pointed inwards.
The structure of the cell membrane is determined by this fact. (See Figure 121, Pg 20 – or next slide)

7. Cell Membrane:

8. Lipids: Fats and Oils
Fats can be stored in what is called adipose tissue where the cells are mainly composed of fats. These lipids act as a store of energy and as insulation against the cold.
This tissue can also act as a protective layer around vital organs such as the heart, liver and kidneys.
Oils are mainly found in plants, not animals, and act only as reserves of energy.

9. Waxes and Steroids
Waxes are a group of lipids produced by both plants and animals and often acts as a protective layer. E.g. Many plants have a waxy cuticle on their leaves that protects from water loss.
Steroids are mostly very large lipids that have important and highly varied functions. Many, if not all, of these functions are vitally important to an organisms wellbeing.
Cholesterol is a common steroid lipid found in animal cells.

10. M6.2: Energetic Polysaccharides
Polysaccharides can also be used by the body to store energy. There are two major examples that are used for the storage of energy in living things.
Starch
Glycogen
Starch is used for energy storage in plants and consists of neatly linked glucose units. It is broken down into glucose in the process of aerobic respiration when required.
Glycogen is differently structured and is found only in animals, mainly in liver and muscle tissues. It is broken down during physical exercise to raise blood sugar levels as needed.

11. Energetic Polysaccharides Cont.
Both Starch and Glycogen are insoluble, meaning they will not dissolve in water.
This makes them easy for the body to store in cellular structures such as vacuoles and granules.
These are much better for energy storage than fats are because they break down much easier. However, they only contain half as much energy.

12. Review: Structural Polysaccharides: Structural Lipids: Energy Storage:
Cellulose – Plant Cell Walls
Chitin – Insect Exoskeletons
Structural Lipids:
Phospholipids – Cell Membranes
Energy Storage:
Oils – Lipids in plants that are stored as Liquids
Fats – Lipids in Animals that are stored as Solids
Starch – Polysaccharide in plants
Glycogen – Polysaccharide in animals