Lipid
Notes
http://www.youtube.com/watch?v=3xF_LK9pnL0&feature=related
Definition: Lipids are molecules composed of carbon, hydrogen and oxygen atoms with many
more hydrogen than oxygen atoms.
 All lipids are insoluble (do NOT dissolve) in water. Can dissolve in non-polar solvents
 One gram of lipid stores more than twice as much chemical energy as one gram of
carbohydrates. This is because lipids contain many bonds between carbon and hydrogen, and
C-H bonds store more energy than Carbon-Oxygen bonds.
 Lipids include many different types of molecules: fatty acids, triglycerides, waxes,
phospholipids, and steroids
1. Fatty Acids – Importance/Function: form triglycerides and phospholipids.
Structure
In the chain of C and H,
the number of C and H differ
in each fatty acid.
 Fatty acids may be saturated (have all single bonds between carbon atoms) or
unsaturated (have mostly single bonds but some double bonds between carbon atoms).
Example:
2. Triglycerides
Structure – they are formed by dehydration synthesis from glycerol and 3 fatty acids.
Glycerol + 3 Fatty Acids  Triglyceride + 3 H2O
+ 3H2O
* Write the molecular formula for a triglyceride formed from glycerol (C3H8O3 or
C3H5(OH)3) and the fatty acids C12H22O2 , C13H26O2 and C14H22O2
FATS – are triglycerides formed from glycerol and 3 saturated fatty acids.
Glycerol + 3 Saturated Fatty Acids  Fat + 3 H2O
 Found in animals
 Solid at room temperature
 Non-polar so do not dissolve in water
 Importance/Function – The major molecule to store food in animals
-
Cushion delicate body organs (kidneys, intestines)
-
Fat under the skin insulates against the cold (especially as blubber
in whales).
-
Carry fat-soluble vitamins in your diet (for interest only these are
A, D. E, K).
OILS – are triglycerides formed from glycerol and 3 unsaturated fatty acids.
Glycerol + 3 Unsaturated Fatty Acids  Oil + 3 H2O
 Found in plants
 Liquid at room temperature
 Importance/Function - Used to store energy in plant seeds (ex: walnut oil, canola
oil) (Most food in plants is stored as starch)
Triglycerides (fats and oils) that you eat are broken down by hydrolysis during digestion.
Triglyceride + 3H2O  Glycerol + 3 Fatty Acids
3. Phospholipids (Diglycerides)
http://www.youtube.com/watch?v=7k2KAfRsZ4Q&feature=related
Structure – they are formed by dehydration synthesis from glycerol, 2 fatty acids and
a phosphate group (H3PO4)
Glycerol + 2 Fatty Acids + Phosphate Group  Phospholipid + 3H2O
The general shape of the phospholipids is:
 Since the phosphate group dissolves in water (hydrophilic = water loving) and the fatty
acids do not (hydrophobic = water hating), phospholipids form a double layer in water.
The phosphate group “heads” are hydrogen bonded to the water and the fatty acid
“tails” are a middle layer away from the water. This is referred to as the Lipid
Bilayer.
 Importance/Function – A double layer of phospholipids forms the basis of all cell
membranes. Because the fatty acid “tails” do not dissolve in water or let water pass
through, the phospholipids form an effective barrier; they keep the water and
dissolved molecules inside the cell separate from the water and dissolve molecules
outside the cell.
4. Steroids
Structure – they are formed of 4 fused carbon rings with various functional groups
attached to the rings.
 Importance/Function – Cholesterol (diagram above) is a steroid that forms part of the
cell membranes in animal cells.
- It can form fatty deposits in blood vessels which contribute
to heart disease or stroke.
 Hormones such as the male and female sex hormones are steroids
5. Waxes
Structure – they are formed from a long chain alcohol molecules and a long fatty acid.
Importance/Function – Form a waterproof coating on plant leaves (Cuticle), animal fur,
feathers and ears.