3.5 Lipids Flashcards
What are lipids?
1) Lipids are molecules containing the elements carbon,hydrogen and oxygen.
2) They are large complex molecules known as macromolecules.
How are triglycerides made?
1) Triglycerides are formed by combining one glycerol molecule with three fatty acids.
2) Glycerol is a member of molecules called alcohols.
3) Fatty acids belong to a group of molecules called carboxylic acids- they consist of a carboxyl group and a variable ‘R’ group hydrocarbon tail.
What bonds do triglycerides contain?
Triglycerides contain ester bonds.
How are triglycerides synthesised?
They are synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule.
Which reaction forms an ester bond?
The condensation reaction forms each ester bond.
What is the process of synthesising triglycerides called?
Esterification
When do triglycerides break down?
Triglycerides break down when the ester bonds are broken. Each ester bond is broken in a hydrolysis reaction.
What are the two types of fatty acids?
Saturated and unsaturated fatty acids. The only difference is their hydrocarbon tails.
Do saturated fatty acids have double bonds between their carbon atoms?
No, they don’t have any double bonds. The general formula for a saturated fatty acid is: CnH(2n+1)COOH
Do unsaturated fatty acids have double bonds between their carbon atoms?
Yes, they have at least one double bond between carbon atoms.
What are phospholipdids?
1) Phospholipids are modified triglycerides.
2) One of the fatty acid molecules is replaced by a phosphate group.
3) The phosphate group is hydrophilic and the fatty acid tails are hydrophobic.
What are the properties of triglycerides?
1) In animals and plants, triglycerides are mainly used as energy storage molecules.
2) Triglycerides are good for storage because:
- The long hydrocarbon tails of the fatty acids contain lots of chemical energy and a lot of energy is released when they are broken down.
- They’re insoluble, so they don’t cause water to enter the cells by osmosis which would make them swell. The triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic.
What are the properties of phospholipids?
1) Phospholipids are found in the cell membranes of all eukaryotes and prokaryotes.
2) They make up whats known as the phospholipid bilayer.
3) Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side.
4) The centre of the bilayer is hydrophobic, so water soluble substances can’t easily pass through it- the membrane acts as a barrier to those substances.
What are the properties of cholesterol?
1) Cholesterol is another type of lipid- it has a hydrocarbon ring structure attached to a hydrocarbon tail.
2) The ring structure has a polar hydroxyl group attached to it.
3) In eukaryotic cells, cholesterol molecules help strengthen the cell membrane by interacting with the phospholipid bilayer.
4) Cholesterol has a small size and a flattened shape- this allows cholesterol to fit in between the phospholipid molecules in the membrane.
5) They bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This helps to make the membrane less fluid and more rigid.
