Chapter 3 - Lipids Flashcards
What chemical elements do lipids contain?
carbon (C), hydrogen (H), and oxygen (O)
However, lipids contain a much lower proportion of oxygen than carbohydrates.
Why are lipids NOT considered polymers?
They are not made made of long chains of monomers
What are lipids?
Large, complex molecules known as macromolecules.
Give 5 functions of lipids:
Energy supply
Structural components
Waterproofing
Insulation
Protection
How are lipids an energy supply?
They can be oxidized to provide energy to cells.
How are lipids a structural component?
Phospholipids are used in cell membranes.
How are lipids waterproofing?
Insoluble lipids are used to form water-resistant barriers.
How are lipids insulation?
Lipids can help retain heat or act as electrical insulators.
How are lipids protection?
Delicate organs are surrounded by a layer of fat.
Describe the structure of lipids
Most lipids are made up of fatty acids combined with an alcohol (usually glycerol).
Describe the structure of fatty acids
Fatty acids consist of a carboxyl group (-COOH) attached to a hydrocarbon chain (R group).
What are the two types of fatty acids?
saturated fatty acids and unsaturated fatty acids
Describe saturated fatty acids
These have hydrocarbon chains that are ‘saturated’ with hydrogen, meaning all carbon atoms are bonded to the maximum number of hydrogen atoms.
The hydrocarbon chain has no carbon-carbon double bonds.
Do lipids that contain saturated fatty acids have higher melting points or not and what does this mean?
Yes and and so are usually solid at room temperature (fats).
Do lipids that contain unsaturated fatty acids have lower melting points and what does this mean?
Yes and so are usually liquid at room temperature (oils).
Describe unsaturated fatty acids
These have hydrocarbon chains that do not contain the maximum number of hydrogen atoms bonded to the carbon atoms.
The hydrocarbon chain has at least one carbon-carbon double bond, which causes the chain to kink.
What 2 forms could unsaturated fatty acids take?
Monounsaturated - One double bond.
Polyunsaturated - Two or more double bonds.
What are the three types of lipids
Triglycerides, Phospholipids & Cholesterol
What are triglycerides?
They are non-polar macromolecules used as a store of energy in animals, plants, and some bacteria.
What is the structure of triglycerides
Formed from on molecule of glycerol and 3 fatty acid chains.
Each fatty acid tail contains a hydrocarbon chain (R) which can vary in length and may be saturated or unsaturated.
What are features that allow triglycerides to store energy efficiently?
- Long hydrocarbon tails
- Low mass to energy ratio
- Insoluble
- High ratio of hydrogen to oxygen atoms
How does having long hydrocarbon tails help triglycerides do their job?
Their many carbon-hydrogen bonds can be broken to release energy.
How does having low mass to energy ratio help triglycerides do their job?
Lots of energy can be stored in a small volume.
How does being insoluble help triglycerides do their job?
They do not affect the water potential of cells as they are large and non-polar.
How does having high ratio of hydrogen to oxygen atoms help triglycerides do their job?
Because triglycerides will release water when oxidised.
How are triglycerides synthesised?
via condensation reactions
How are triglycerides broken down?
via hydrolysis reactions
Describe a condensation reaction that makes a triglyceride
The hydroxyl groups (OH) on the glycerol and on the three fatty acids react together to release three water molecules (H2O).
This results in three ester bonds between the glycerol and the fatty acids.
Describe a hydrolysis reaction that breaks down a triglyceride
The addition of three water molecules (H2O) breaks the ester bonds.
This separates the glycerol and the fatty acids.
What is a phospholipid?
A phospholipid is a type of lipid used as a structural component of the cell membrane.
Describe the structure of a phospholipid
They are similar to triglycerides except one of the fatty acid tails is replaced by a phosphate group.
They have a: hydrophilic ‘head’ - This contains glycerol and phosphate.
And a hydrophobic ‘tail’ - This contains fatty acids.
How are the head ad the tail in a phospholipid different to each other?
The phosphate group is polar and so attracts water (hydrophilic) whereas the fatty acid tails repel water (hydrophobic).
How do phospholipids align themselves when placed in water?
When phospholipids are placed in water, they arrange themselves into a double layer (bilayer) so that the hydrophilic heads are facing out (towards the water) and the hydrophobic tails are facing in (away from the water).
This arrangement creates a hydrophobic centre in the bilayer so that water-soluble substances cannot pass through.
What is cholesterol and what is it used for?
Cholesterol is a type of lipid known as a sterol and is used by animal cells to increase the stability of the cell membrane.
Cholesterol is also used to make vitamin D, steroid hormones, and bile.
Describe the structure of cholesterol
Like phospholipids, cholesterol is a polar molecule. The hydroxyl group (OH) is hydrophilic whereas the rest of the molecule is hydrophobic
What is the role of cholesterol in the cell membrane?
Cholesterol binds to phospholipid fatty acid tails, causing the phospholipids to pack more closely together. This reduces the fluidity of the cell membrane, and increases the stabilty.
