Biological Molecules 1: Lipids Flashcards
What are the five key characteristics of lipids?
Long-chain molecules
Insoluble in water
Soluble in membranes
Exist as oily liquids or waxy solids
Can form salts
What type of chain-length is most common for natural fatty acids?
Even-number chain lengths
Describe the meaning of the naming convention for fatty acids, e.g. 18:3(n-3)
The first number (18) shows number of carbons in the chain
The second number (3) shows how many double bonds are present
The (n-3) shows the position of the first double bond from the end of the chain
What is hydrogenation of polyunsaturated vegetable oils used for?
Polyunsaturated fatty acids contain multiple double bonds - prevents packing of molecules so causes lower boiling points
Hydrogenation removes these double bonds, therefore increasing boiling point
Useful to make the molecule more solid (e.g. for margarine)
Can form trans isomers which are implicated in heart disease
What is the typical stereochemistry of natural fatty acids?
Cis
Describe and explain how boiling point changes as you increase the degree of unsaturation in a fatty acid.
More double bonds = decreasing the melting point
Because the molecules curl and don’t pack together as neatly causing intermolecular forces to weaken - lowering the melting point
Makes the compound more rigid
Why are saturated fatty acids generally solid fats?
Because they have strong intermolecular forces due to the flexibility of their chains and ability to pack together tightly due to lack of double bonds
What are triglycerides used for?
Storing energy in the body
What do triglycerides consist of?
Glycerol
3 fatty acids
What do highly saturated triglycerides look like?
Solid fats
E.g. butter
What do highly unsaturated triglycerides look like?
Liquid oils
E.g. olive oil
How are triglycerides transported around the body?
By carrier proteins
First the ester bonds within the molecule must be hydrolysed by enzymes
Fatty acids then pass into the cells for metabolism
What are phospholipids?
2 fatty acid tails (hydrophobic)
Phosphate head (hydrophilic)
*Sometimes an amino group is substituted onto the phosphate group
What are the three possible amino groups that can be substituted onto the phosphate head of a phospholipid?
Serine
Ethanolamine
Choline
Why are phospholipids biologically significant?
Cell membranes - phospholipid bilayer
Allows cells to be isolated from external environment
Also allows creation of distinct organelles - keeps the contents separate
