What are the most common lipids?
Triglycerides and phospholipids
Are lipids hydrophobic or hydrophilic?
Hydrophobic
What are triglycerides used for?
Insulation, storage, and protection of organs
Why are triglycerides good for energy storage?
When oxidized, they yield more energy per unit mass than carbohydrates
Why are triglycerides not good for quick energy?
They can’t be mobilised quickly because they are very insoluble.
What are triglycerides made from?
One glycerol molecule and three fatty acid molecules
What is the R group of fatty acids?
COOH
What is the structure of fatty acids?
- made of non-polar hydrocarbon chains with a polar carboxyl acid group at one end.
How are triglycerides formed?
- 3 Fatty acid molecules
- 1 glycerol molecule
- 3 condensation reactions to form 3 ester bonds
- 3 water molecules also produced
Structure of an ester bond
O=C
Whats the difference between saturated and unsaturated fatty acids?
Unsaturated fatty acids have C=C double bonds, whereas saturated fatty acids have no C=C double bonds
What are some features of triglycerides with saturated fatty acids?
- High melting points
- Found in warm blooded animals
- Solid at room temperature
What are some features of triglycerides with unsaturated fatty acids?
- Low melting points
- Found in cold blooded animals
- Liquid at room temperature
What is the difference between monounsaturated and polyunsaturated fatty acids.
Polyunsaturated fatty acids have more than one C=C bond, monounsaturated acids only have one C=C bond.
What makes a phosphodiester bond different to a triglyceride?
They have a phosphate group
What is the structure of a phospholipid?
- Polar hydrophilic ‘head’ (the negatively charged phosphate group)
- Two non-polar hydrophobic ‘tails’ (fatty acid chains)
Which type of bond joins the glycerol molecule to the phosphate group?
Phosphoester bond
What happens when phospholipids are mixed with water?
- FORM A LIPOSOME
- Double-layered phospholipid bilayer (the hydrophilic heads face the water and the hydrophobic tails face eachother
What is the biochemical test for lipids?
The alcohol emulsion test
What is the method for the alcohol emulsion test?
- Shake the sample with ethanol
- Decant the liquid into water
- A positive test will result in a cloudy emulsion forming because the lipids dissolved in ethanol will form a precipitate.
