Lipids Flashcards
What are the two types of lipids?
- Triglycerides
- Phospholipids
What are the bonds which form between lipids?
Ester bonds
How many water molecules are formed when a triglyceride is formed?
The condensation reaction produces 3 ester bonds and 3 water molecules.
When a hydrolysis reaction occurs, what happens to the triglyceride?
It is split by the addition of 3 water molecules (which breaks the 3 ester bonds)
What do all lipids contain?
Carbon
Hydrogen
Oxygen
What property of lipids means they cannot dissolve in water?
Lipids are insoluble because they are non-polar molecules so aren’t attracted to water.
Why are lipids non polar molecules?
They have a large number of carbon and hydrogen molecules.
What type of substances are lipids soluble in?
They are soluble in other organic solvents e.g alcohol.
Where are triglycerides found?
They are components of our diet (in fats and oils) which are stored in fat cells in the body.
What are triglycerides made from?
- 1 glycerol
- 3 fatty acids
What forms a fatty acid?
- long hydrocarbon chain
- carboxyl group (COOH)
Why aren’t lipids polymers?
They are made from different subunits, not similar repeating units
What is the test for lipids? (Describe it)
- mix the sample being tested with alcohol (ethanol) in a test tube
- shake tube thoroughly and add cold water
- if a milky white emulsion is formed then this indicates the presence of a lipid
What is the positive result of the lipid test?
Milky white emulsion forms.
What is a saturated fatty acid?
They only have single carbon to carbon bonds, so form a linear carbon chain.
What is an unsaturated fatty acid?
They have one or more carbon to carbon double bond which form a bent chain
What causes unsaturated fatty acid chains to bend?
Carbon to carbon double bonds
Why do saturated fatty acids have a high melting point?
The intermolecular forces between the chains are strong and require a lot of energy to overcome
What property does a high melting point give saturated fatty acid?
It means they are a solid at room temperature e.g. butter
Why do unsaturated fatty acids have a low melting point?
As the fatty acid chains are bent, they form an irregular pattern and cannot fit tightly together.
This means the intermolecular attractions are weaker so are more easily broken.
What property does a low melting point give unsaturated fatty acids?
It means they are liquid at room temperature,
E.g vegetable oils.
Where are phospholipids found?
In cell membranes
Compare phospholipids structure to triglycerides structure
Triglycerides are formed from one glycerol and 3 fatty acids.
Phospholipids are formed from a phosphate group, glycerol and 2 fatty acids.
Why are phospholipids polar?
The phosphate group has a negative charge which means it’s slightly attracted to hydrogen molecules in water
Why do phospholipids have hydrophilic heads?
The phosphate group is negative and so attracted to the slightly positive of hydrogen in water.
Why do phospholipids have a hydrophobic tail?
The fatty acids are neutral (non polar) so not attracted to water.
What are the 6 roles of lipids?
- source of energy
- waterproofing
- insulation
- protection
- buoyancy
- electrical insulator
How do lipids provide waterproofing?
Waxy lipid cuticles found in plants conserve water (reduce loss)
How do lipids provide insulation?
Fats are slow conductors of heat and a layer of fat stored under the skin can retain heat
How do lipids provide buoyancy?
Fats are less dense than water so can help some organisms float e.g a seal
How do lipids provide protection
They are often found around delicate organs like kidneys
How do lipids provide electrical insulation?
They surround the nerves to increase the speed of electrical impulses
