3: Lipids Flashcards
What are lipids?
Commonly known as fats and oils, they are molecules containing carbon hydrogen and oxygen
What is the difference between fats and oils?
Fats are lipids that are solid at room temperature. Oils are lipids that are liquid at room temperature
Why are lipids insoluble in water?
They are non-polar as electrons in their outer orbitals are more evenly distributed than in polar molecules so there are no positive or negative areas within the molecules
Lipids are macromolecules. What is a macromolecule?
Large, complex molecules which are not built from repeating units
How is a triglyceride made?
Combining one glycerol molecule with three fatty acids.
Glycerol is an alcohol
Fatty acids are carboxylic acids
How does glycerol and three fatty acids react? What are the bonds formed called?
Hence what is the reaction called?
Hydroxyl groups on all the molecules interact, leading to formation of three water molecules and bonds between fatty acids and the glycerol molecule. The bonds formed are called ester bonds so the reaction is called esterification. Esterification is a condensation reaction
How is esterification reversed/how are triglycerides broken down?
Hydrolysis - three water molecules need to be supplied to reverse the reaction
What does it mean when a molecule is saturated?
It has no double bonds between carbon atoms
What does it mean when a molecule is unsaturated?
It has double bonds between some of the carbon atoms.
One double bond = monounsaturated
Multiple double bonds = polyunsaturated
Why are oils liquid at room temperature?
The presence of double bonds causes the molecule to bend/kink and they therefore cannot pack so closely together
What are phospholipids?
A modified triglyceride with a phosphate head and two fatty acid tails
What is a feature of the phosphate heads?
They are charged so will interact with water and are therefore hydrophilic
What is a feature of the tails?
They are non-polar so are repelled by water and are therefore hydrophobic
How do phospholipids form a bilayer?
Form a two-layered sheet formation (bilayer) with the hydrophobic tails pointing towards the centre, protected from the water by the hydrophilic heads
What are sterols?
Complex alcohol molecules, based on a four carbon ring structure with a hydroxyl group at one end
